An efficient irrigation method to promote grain filling by regulating the greening trait of rice.

Abstract

This invention discloses a highly efficient irrigation method for promoting grain filling by regulating the chlorosis trait in rice. This method involves shallow-water-drying quantitative irrigation, where water is naturally allowed to dry from a shallow water layer to a specified soil water potential before being re-irrigated to a shallow water layer, and this cycle is repeated. First, the presence of chlorosis in rice plants is determined based on a leaf color threshold. Then, for varieties exhibiting chlorosis, the degree of soil drying at each growth stage is quantitatively determined based on the panicle type of different rice subspecies and leaf age patterns. This method, by controlling field water potential, creates mild water stress on the plants, thereby regulating plant senescence (i.e., chlorosis trait). It also enhances the activity of key enzymes in sucrose-starch metabolism in the stem sheath and grains, thus promoting the translocation of assimilates from the stem sheath to the grains, increasing grain filling rate, and achieving yield increase.

Description

Technical Field

[0001] This invention relates to an efficient irrigation method that promotes grain filling by regulating the greening trait of rice, belonging to the field of agricultural technology. Background Technology

[0002] In pursuit of high yields, excessive nitrogen fertilizer input and overly vigorous vegetative growth in some high-yielding varieties lead to delayed maturity and chlorosis in rice, a trait known as chlorosis retardation (Sakur et al., 2014; Cao et al., 2022). Chlorosis retardation refers to the phenomenon where chlorophyll does not degrade or degrades slowly during leaf senescence, resulting in low translocation rates of photosynthetic assimilates to grains and poor grain filling, causing yield losses of approximately 20% (Hu et al., 2022; Okamura et al., 2018; Yamamoto et al., 2017). Therefore, regulating chlorophyll degradation and coordinating the relationship between rice plant senescence and assimilate translocation to grains are of great significance for achieving green rice production.

[0003] Current research, both domestically and internationally, mainly focuses on the cloning and functional analysis of genes related to chlorophyll stagnation. Ten cloned rice chlorophyll stagnation mutant genes are associated with chloroplast development and chlorophyll degradation, namely OsSGR, SGRL, NYC1, NOL, RLS1, NYC3, OsPAO, OsRCCR1, OsABC1-2, and NYC4 (Cackett et al., 2022; Chen et al., 2016). Most of these genes encode enzymes with specific functions, thereby regulating the rate of chlorophyll degradation. However, single-gene regulation cannot effectively control plant senescence (Guo et al., 2021; Havé et al., 2017). Plant senescence is regulated by various internal factors (plant nutritional status; endogenous hormones such as abscisic acid, ethylene, cytokinins, etc.) and external factors (water, temperature, light, etc.) (Jian et al., 2023; Cortleven et al., 2019; Chen et al., 2021).

[0004] Currently, water management is commonly used in production to regulate the chlorotic trait (Shin et al., 2020). Drought stress after rice flowering typically leads to premature senescence and reduced photosynthesis. While it accelerates grain filling, it cannot compensate for yield losses caused by the shortened growth period (Yang et al., 2017; Zhang et al., 2021). However, under moderate soil drought conditions, leaf photosynthesis is not severely inhibited, and the translocation of non-structural carbohydrates (NSCs) in the stem sheath is increased, thereby promoting grain filling (Ding et al., 2023; Yang et al., 2023; Ni et al., 2022). Studies have shown that moderate soil drought after rice flowering can increase the abscisic acid to ethylene ratio in grains, promoting starch accumulation and thus grain filling (Wang and Zhang, 2020). Many water-saving irrigation techniques exist for regulating moderate soil drought after rice flowering, such as controlled irrigation and intermittent irrigation, but their yield-increasing effects are not significant or stable (Nguyen et al., 2021; Salam et al., 2021). Currently, there is a lack of efficient irrigation methods that can regulate the greening trait of rice to promote grain filling. Summary of the Invention

[0005] Objective: The purpose of this invention is to provide an efficient irrigation method that promotes grain filling by regulating the chlorosis trait in rice. This method primarily addresses the problem of delayed maturity (chlorosis trait) in rice caused by excessive nitrogen fertilizer input and the overly vigorous vegetative growth of some high-yielding varieties. By promoting the translocation of assimilates to the grains, the method increases the grain filling rate. The principle is based on the fact that rice plant senescence is regulated by water conditions. Water stress promotes timely and moderate senescence in the plants, enhancing the activity of key enzymes in sucrose-starch metabolism during grain filling. Based on the characteristics of different panicle types and their responses to field water at different growth stages, the optimal drying water potential value for promoting grain filling is determined. This allows for quantitative, light-dry irrigation, effectively regulating the chlorosis trait and promoting grain filling.

[0006] Technical Solution: This invention provides an efficient irrigation method for promoting grain filling by regulating the chlorosis trait of rice. The method determines whether rice plants exhibit chlorosis based on the rice leaf color threshold. For rice plants exhibiting chlorosis, the method determines the appropriate soil water potential index for each growth stage based on the rice variety, panicle size, and leaf age pattern. The method then performs light, shallow water-drying quantitative irrigation, that is, watering is carried out again when the shallow water layer naturally dries to the specified soil water potential, and this cycle continues until the rice is harvested.

[0007] Furthermore, the rice varieties include indica rice varieties and japonica rice varieties.

[0008] Furthermore, the spikelet type includes large spikelet type, medium spikelet type, and small spikelet type.

[0009] Furthermore, the leaf age pattern is divided into the following stages: after transplanting to the 4th leaf stage, the 4th leaf stage to the N-n leaf stage, the N-n leaf stage to the N-n+3 leaf stage, the N-n+3 leaf stage to the 4th leaf stage from the top, the 4th leaf stage from the top to the 3.1th leaf stage from the top, the 3.0th leaf stage from the top to the 2.1st leaf stage from the top, the 2.0th leaf stage from the top to the 0.8th leaf stage, the 0.7th leaf stage from the top to the 0th leaf stage, the 0th leaf stage from the top to 45 days after heading, and 45 days after heading to harvest. Here, N = total number of leaves on the main stem, generally 11 to 19 leaves, which varies depending on the rice variety; n = number of elongated internodes, generally 4 to 7 elongated internodes, which varies depending on the rice variety.

[0010] Furthermore, for indica rice varieties: those with ≥200 grains per panicle are large-panicle varieties, those with 150 < grains per panicle < 200 are medium-panicle varieties, and those with ≤150 grains per panicle are small-panicle varieties.

[0011] Furthermore, for japonica rice varieties: those with ≥170 grains per panicle are large-panicle varieties, those with 120 < grains per panicle <170 are medium-panicle varieties, and those with ≤120 grains per panicle are small-panicle varieties.

[0012] Furthermore, the water depth of the submerged layer is 2 to 3 cm.

[0013] Furthermore, the soil water potential is -15 kPa to -3 kPa.

[0014] Furthermore, the efficient irrigation method includes the following steps:

[0015] (1) From transplanting to the 4th leaf stage (the leaf age at the beginning of tillering): maintain a shallow water layer of 2-3 cm in the field;

[0016] (2) From the 4th leaf stage (the leaf age at the beginning of tillering) to the N-n leaf stage (the critical leaf age for effective tillering, where N = the total number of leaves on the main stem and n = the number of elongated internodes): the soil naturally dries from a water level of 2-3 cm. Depending on the rice variety, when the water potential is between -10 kPa and -3 kPa, the soil is irrigated to a shallow water layer of 2-3 cm, and then allowed to dry naturally again. This cycle is repeated. No irrigation is allowed in the field until the soil water potential reaches the above-mentioned index value.

[0017] (3) From the N-n leaf stage (critical leaf age for effective tillering, N = total number of leaves on the main stem; n = number of elongated internodes) to the N-n+3 leaf stage (leaf age at the beginning of jointing, N = total number of leaves on the main stem; n = number of elongated internodes): let the soil naturally dry from a water level of 2-3 cm. Depending on the rice variety, when the water potential is -12 kPa to -5 kPa, irrigate to a shallow water layer of 2-3 cm, and then let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

[0018] (4) From the N-n+3 leaf stage (the leaf age at the beginning of jointing, N = the total number of leaves on the main stem; n = the number of elongated internodes) to the 4th leaf stage (the leaf age at the beginning of panicle differentiation): let the water naturally dry from the groundwater layer of 2-3 cm. Depending on the rice variety, when the water potential is -10 kPa to -3 kPa, irrigate to a shallow water layer of 2-3 cm, and then let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

[0019] (5) 4-3.1 leaf stage from the bottom (bud differentiation stage), 3.0-2.1 leaf stage from the bottom (branch differentiation stage) and 2.0-0.8 leaf stage from the bottom (floret differentiation stage): let the water naturally dry from the groundwater layer of 2-3 cm. Depending on the rice variety, when the water potential is -12 kPa to -5 kPa, irrigate again to a water layer of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

[0020] (6) 0.7-0 leaf stage (pollen mother cell formation and meiosis stage): let the water dry naturally from the groundwater layer of 2-3 cm. Depending on the rice variety, when the water potential is -15KPa to -7KPa, irrigate to a shallow water layer of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

[0021] (7) From the zero-leaf stage to 45 days after heading and from 45 days after heading to harvest: let the water naturally dry from the groundwater layer of 2-3 cm. Depending on the rice variety, when the water potential is -15KPa to -12KPa, irrigate to a water layer of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

[0022] Furthermore, N = total number of leaves on the main stem, which is generally 11 to 19 leaves, varying depending on the rice variety; n = number of elongated internodes, which is generally 14 to 7 elongated internodes, varying depending on the rice variety.

[0023] Furthermore, in step (2), the different drying potentials of rice varieties ranging from -10KPa to -3KPa are specifically as follows: for indica rice varieties, the drying potential is -5KPa for large-spike varieties, -7.5KPa for medium-spike varieties, and -10KPa for small-spike varieties; for japonica rice varieties, the drying potential is -3KPa for large-spike varieties, -5KPa for medium-spike varieties, and -7KPa for small-spike varieties.

[0024] Furthermore, in step (3), the different drying potentials of rice varieties ranging from -12KPa to -5KPa are specifically as follows: for indica rice varieties, the drying potential for large-spike varieties is -7.5KPa, for medium-spike varieties it is -10KPa, and for small-spike varieties it is -12KPa; for japonica rice varieties, the drying potential for large-spike varieties is -5KPa, for medium-spike varieties it is -7KPa, and for small-spike varieties it is -10KPa.

[0025] Furthermore, in step (4), the different drying potentials of rice varieties are -10KPa to -3KPa. Specifically, for indica rice varieties, the drying potential is -10KPa for large-spike varieties, -7.5KPa for medium-spike varieties, and -5KPa for small-spike varieties; for japonica rice varieties, the drying potential is -7KPa for large-spike varieties, -5KPa for medium-spike varieties, and -3KPa for small-spike varieties.

[0026] Furthermore, in step (5), during the 4th to 3.1th leaf stage (bract differentiation stage), the drying potential of different rice varieties is -12KPa to -5KPa. Specifically, for indica rice varieties, the drying potential is -12KPa for large-panicle varieties, -9KPa for medium-panicle varieties, and -7.5KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -10KPa for large-panicle varieties, -7KPa for medium-panicle varieties, and -5KPa for small-panicle varieties.

[0027] Furthermore, in step (5), during the 3.0 to 2.1 leaf stage (branch differentiation stage), the water potential for different rice varieties is -12KPa to -5KPa. Specifically, for indica rice varieties, the water potential for large-spike varieties is -12KPa, for medium-spike varieties it is -9KPa, and for small-spike varieties it is -7.5KPa; for japonica rice varieties, the water potential for large-spike varieties is -10KPa, for medium-spike varieties it is -7KPa, and for small-spike varieties it is -5KPa.

[0028] Furthermore, in step (5), during the 2.0 to 0.8 leaf stage (parallel flower differentiation stage), the drying potential of different rice varieties is -12KPa to -5KPa. Specifically, for indica rice varieties, the drying potential is -8KPa for large-panicle varieties, -10KPa for medium-panicle varieties, and -12KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -5KPa for large-panicle varieties, -7KPa for medium-panicle varieties, and -10KPa for small-panicle varieties.

[0029] Furthermore, in step (6), the different drying potentials of the rice varieties are -15KPa to -7KPa. Specifically, for indica rice varieties, the drying potential is -10KPa for large-spike varieties, -12KPa for medium-spike varieties, and -15KPa for small-spike varieties; for japonica rice varieties, the drying potential is -7KPa for large-spike varieties, -10KPa for medium-spike varieties, and -12KPa for small-spike varieties.

[0030] Furthermore, in step (7), from the 0-leaf stage to 45 days after heading, the drying potential of different rice varieties is -15KPa to -12KPa. Specifically, for indica rice varieties, the drying potential is -15KPa for large-panicle varieties, -15KPa for medium-panicle varieties, and -15KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -12KPa for large-panicle varieties, -12KPa for medium-panicle varieties, and -12KPa for small-panicle varieties.

[0031] Furthermore, in step (7), from 45 days after heading to harvest, the drying potential of different rice varieties is -15KPa to -12KPa. Specifically, for indica rice varieties, the drying potential is -15KPa for large-panicle varieties, -15KPa for medium-panicle varieties, and -15KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -12KPa for large-panicle varieties, -12KPa for medium-panicle varieties, and -12KPa for small-panicle varieties.

[0032] The soil water potential mentioned in this invention can be measured using a soil moisture tensiometer. Several companies in China manufacture and sell this device, such as Beijing Haifuda Technology Co., Ltd.'s ZXKH-60 soil moisture tensiometer and Beijing Zhonghui Tiancheng Technology Co., Ltd.'s ZKNT-100 soil moisture tensiometer; choosing one model is sufficient. The manufacturer will provide an instruction manual with the soil moisture tensiometer. Soil moisture tensiometers are inexpensive, easy to use, and accurate and reliable. Under the same soil water potential, the effectiveness of plants in utilizing soil water is essentially the same regardless of whether it is sandy soil, loam, or clay. Therefore, the same soil water potential index can be used for all types of soil.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0034] This invention addresses the issues of stunted greening, low translocation rate of photosynthetic assimilates to grains, and poor grain filling in rice production caused by high nitrogen fertilizer input and excessive vegetative growth in some high-yielding varieties. It determines whether stunted greening occurs based on leaf color thresholds (41 for indica rice and 43.5 for japonica rice from the 4th leaf stage to the Nnth leaf stage (critical leaf age for effective tillering); 36.5 for indica rice and 39 for japonica rice from the Nnth leaf stage (critical leaf age for effective tillering) to the 0th leaf stage (lower leaf stage); and 22.0 for indica rice and 28.5 for japonica rice from the 0th leaf stage to heading and maturity stage). For rice varieties exhibiting chlorosis, considering panicle size and leaf age patterns, the degree of soil desiccation at each growth stage is quantified. Irrigation is then adjusted based on this desiccation level, employing a shallow-water-drying quantitative irrigation method. The soil is allowed to naturally dry from the shallow water layer to a designated water level before re-irrigating to the shallow water layer, and this cycle is repeated. By controlling the field water potential, a mild water stress is created on the plants, thereby regulating plant senescence (i.e., chlorosis). This method also enhances the activity of key enzymes in sucrose-starch metabolism in the stem sheath and grains, promoting the translocation of assimilates from the stem sheath to the grains, increasing grain filling rate, and ultimately increasing yield. Detailed Implementation

[0035] The technical solution of the present invention will be further described below.

[0036] Example 1: Effects of an efficient irrigation method that promotes grain filling by regulating the greening trait in rice on yield and related physiological traits of different panicle types (indica and japonica rice).

[0037] 1. Tested varieties and cultivation conditions

[0038] The experiment was conducted at the Experimental Farm of Yangzhou University (Yangzhou, Jiangsu Province) in 2021 and 2022. The previous crop in the experimental field was wheat, the soil texture was sandy loam, and the topsoil contained 2.12% organic matter, 93.2 mg / kg available nitrogen, 20.5 mg / kg available phosphorus, and 83.6 mg / kg available potassium.

[0039] The tested varieties were Nanjing 46 (japonica rice, large panicle type), Wuyunjing 24 (japonica rice, medium panicle type), Wuyunjing 7 (japonica rice, small panicle type), Liangyou 1266 (indica rice, large panicle type), Liangyou 383 (indica rice, medium panicle type), and Yangxianyou 68 (indica rice, small panicle type). Table 1 shows the criteria for determining panicle type in different rice varieties.

[0040] Table 1. Determination of panicle type among different rice varieties

[0041] Variety type Large spike type medium-sized spike spikelet type Indica rice ≥200 grains per ear 150 < number of grains per ear < 200 ≤150 grains per ear Japonica rice ≥170 grains per ear 120 < number of grains per ear < 170 ≤120 grains per ear

[0042] Seedlings were raised in seedbeds on May 20th and transplanted on June 13th. Two rice seedlings were transplanted per hole, with a spacing of 10.7cm x 30cm. The soil bulk density was 1.33g / cm³.-3 .

[0043] The experiment employed a completely randomized block design, replicated three times. Each plot was 5 × 6 m in size, separated by 1 m wide trenches, with plastic film inserted 0.5 m deep into the soil to form a barrier. Nitrogen fertilizer (270 kg ha) was applied at the following ratios: before transplanting, at the N–n leaf stage (critical leaf age for effective tillering, where N = total number of leaves on the main stem; n = number of elongated internodes), at the 4-leaf stage (leaf age at the beginning of panicle differentiation), and at the 0-leaf stage. -1 Apply phosphorus (30 kg ha) before transplanting. -1 (superphosphate) and potassium (40kg ha) -1 Potassium chloride is used as a base fertilizer.

[0044] 2. Irrigation treatment

[0045] A three-factor experiment was conducted, considering irrigation method, rice variety, and rice panicle type. Irrigation method (A) was the main plot, rice variety (B) was the main subplot, and rice panicle type (C) was the secondary subplot. The plot area was 20 m². 2 Randomized block design, repeated 3 times. Starting one day after heading (when 51% of the rice panicles have emerged from the flag leaf sheath), two irrigation methods were implemented: A1, conventional irrigation: maintaining a shallow water layer of 2-3 cm in the field, stopping irrigation one week before harvest (control); A2, the mild shallow-water-drying quantitative irrigation of this invention (mild-drying quantitative irrigation): First, the chlorophyll (SPAD) value of the fully expanded uppermost leaves of the rice was measured using a SPAD-502 chlorophyll meter. Based on the rice leaf color threshold in Table 2, it was determined whether the rice plants exhibited chlorosis (the principle is based on the chlorophyll spectral absorption law, using two different light-emitting tubes to irradiate the leaves). The method involves measuring the intensity of light transmitted through the leaves to calculate the relative chlorophyll content or greenness of the leaves. During measurement, the leaves are simply clamped together; there is no need to harvest them, thus not affecting normal crop growth. Leaf monitoring can be conducted throughout the crop's growth process, resulting in more scientific analysis results. For rice exhibiting stunted greening, a soil water tensiometer is used to monitor soil water potential. Water potential stress is assessed for different rice varieties and panicle types at different growth stages. Irrigation is then conducted according to the soil water potential thresholds in Table 3. Tap water pipes are installed for irrigation, and water meters are installed on the pipes to monitor the irrigation volume. Rain shelters are used to protect the rice from rain.

[0046] The specific method of the present invention for light, shallow-water-drying quantitative irrigation is as follows:

[0047] (1) From transplanting to the 4th leaf stage (the leaf age at the beginning of tillering): always maintain a shallow water layer of 2-3 cm in the field.

[0048] (2) 4th leaf stage (leaf age at the beginning of tillering) to N–n leaf stage (critical leaf age for effective tillering, N = total number of leaves on the main stem; n = number of elongated internodes):

[0049] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -5 kPa for large-panicle varieties, -7.5 kPa for medium-panicle varieties, and -10 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -3 kPa for large-panicle varieties, -5 kPa for medium-panicle varieties, and -7 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0050] (3) From the N-n leaf stage (critical leaf age for effective tillering, N = total number of leaves on the main stem; n = number of elongated internodes) to the N-n+3 leaf stage (leaf age at the beginning of jointing, N = total number of leaves on the main stem; n = number of elongated internodes):

[0051] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -7.5 kPa for large-panicle varieties, -10 kPa for medium-panicle varieties, and -12 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -5 kPa for large-panicle varieties, -7 kPa for medium-panicle varieties, and -10 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0052] (4) From the N-n+3 leaf stage (leaf age at the beginning of jointing, N = total number of leaves on the main stem; n = number of elongated internodes) to the 4th leaf stage (leaf age at the beginning of panicle differentiation):

[0053] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -10 kPa for large-panicle varieties, -7.5 kPa for medium-panicle varieties, and -5 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -7 kPa for large-panicle varieties, -5 kPa for medium-panicle varieties, and -3 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0054] (5) From the 4th to the 3.1st leaf stage (bud differentiation stage):

[0055] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -12 kPa for large-panicle varieties, -9 kPa for medium-panicle varieties, and -7.5 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -10 kPa for large-panicle varieties, -7 kPa for medium-panicle varieties, and -5 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0056] (6) 3.0–2.1 leaf stage (branch differentiation stage):

[0057] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -12 kPa for large-panicle varieties, -9 kPa for medium-panicle varieties, and -7.5 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -10 kPa for large-panicle varieties, -7 kPa for medium-panicle varieties, and -5 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0058] (7) 2.0–0.8 leaf stage (floret differentiation stage):

[0059] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -8 kPa for large-panicle varieties, -10 kPa for medium-panicle varieties, and -12 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -5 kPa for large-panicle varieties, -7 kPa for medium-panicle varieties, and -10 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0060] (8) 0.7–0 leaf stage (pollen mother cell formation and meiosis stage):

[0061] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -10 kPa for large-panicle varieties, -12 kPa for medium-panicle varieties, and -15 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -7 kPa for large-panicle varieties, -10 kPa for medium-panicle varieties, and -12 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values.

[0062] (9) From the zero-leaf stage to 45 days after heading:

[0063] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -15 kPa for large-panicle varieties, -15 kPa for medium-panicle varieties, and -15 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -12 kPa for large-panicle varieties, -12 kPa for medium-panicle varieties, and -12 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned index values.

[0064] (10) From 45 days after heading to harvest:

[0065] Irrigate the field to a water layer of 2-3 cm, then allow it to dry naturally. According to Table 3, which sets water potential stress standards for different rice panicle types at different growth stages, for indica rice varieties, the water potential at the dry-dry stage is -15 kPa for large-panicle varieties, -15 kPa for medium-panicle varieties, and -15 kPa for small-panicle varieties; for japonica rice varieties, the water potential at the dry-dry stage is -12 kPa for large-panicle varieties, -12 kPa for medium-panicle varieties, and -12 kPa for small-panicle varieties. Irrigate to a water layer of 2-3 cm, then allow it to dry naturally. Repeat this cycle. Do not irrigate the field until the soil water potential reaches the above-mentioned values, until harvest.

[0066] Wherein, N = total number of leaves on the main stem, N = 17 for Wuyunjing 24, N = 16 for Wuyunjing 7, N = 15 for Nanjing 46; N = 18 for Liangyou 1266, N = 17 for Liangyou 383, and N = 15 for Yangxianyou 68; n = number of elongated internodes, n = 5 for Wuyunjing 24, n = 5 for Wuyunjing 7, n = 5 for Nanjing 46, n = 6 for Liangyou 1266, n = 5 for Liangyou 383, and n = 5 for Yangxianyou 68.

[0067] Table 2 shows the SPAD value range for judging rice chlorosis based on the fully expanded leaves at the top of the plant.

[0068]

[0069] Table 3. Soil water potential thresholds for irrigation based on rice grain size and growth stage.

[0070]

[0071]

[0072] 3. Sampling and testing

[0073] Samples were taken at 8, 20, and 32 days after heading. The activities of key enzymes involved in starch hydrolysis in rice stems and sheaths (α-amylase and β-amylase), and key enzymes involved in starch synthesis in grains (granule-bound starch synthase (GBSS) and starch branching enzyme (SBE)) were determined according to the methods for determining the activity of key enzymes in starch metabolism in Chapter 3, Dry Matter Accumulation and Material Transport Measurement, of the *Handbook of Plant Physiology Experiments*. Chlorophyll content in flag leaves, non-structural carbohydrate (NSC) content in stems and sheaths, and grain weight changes were also measured. At maturity (one day before harvest), 10 rice plants from each plot were sampled for determining yield components. A 5m² harvest was also taken. 2 Production was calculated. The results are shown in Table 4-9.

[0074] In Table 4-9:

[0075] Each rice variety is planted in fields equipped with rain shelters, which are then covered when it rains.

[0076] Conventional irrigation as a control: that is, maintaining a shallow water layer of 2-3 cm in the field and stopping irrigation one week before harvest;

[0077] Light-dry-wet quantitative irrigation: This is the irrigation method of the present invention. When the soil water potential in the field reaches the index value in the table, a shallow water layer of 2-3 cm is irrigated. The soil then dries naturally to the index value, and irrigates again. The soil then dries naturally again, and the cycle is repeated. If the soil water potential in the field is greater than the index value, no irrigation is required.

[0078] Yield refers to the actual yield of each plot; the number of spikelets, seed setting rate and thousand-grain weight are the measured values ​​of 10 rice plants in each plot.

[0079] Different letters a and b indicate significant differences from the control at the P=0.05 level, comparing two irrigation methods within the same variety and the same pen.

[0080] Table 4. Effects of light dry and wet quantitative irrigation on the yield of different rice varieties.

[0081]

[0082]

[0083] As shown in Table 4, compared with conventional irrigation (control), light dry-wet quantitative irrigation significantly improved the seed setting rate, thousand-grain weight, and yield of rice. Analysis of the yield components revealed that the main reason for the increased yield was the improved seed setting rate. Specifically, the seed setting rate increased by 1.66%–9.03%, the thousand-grain weight increased by 0.34%–4.78%, and the yield increased by 7.33%–12.04%. While there were differences in the number of panicles per unit area, the number of grains per panicle, and the thousand-grain weight, these differences were not significant.

[0084] Table 5. Effects of light dry and wet quantitative irrigation on chlorophyll content in flag leaves of different rice varieties.

[0085]

[0086] As shown in Table 5, compared with the conventional irrigation control, the light dry-wet quantitative irrigation significantly reduced the chlorophyll content of the flag leaf at each measurement period, promoted plant senescence, and effectively regulated the chlorosis trait of the plant.

[0087] Table 6. Effects of light dry and wet quantitative irrigation on the activities of α-amylase and β-amylase in post-flowering stem sheaths of different rice varieties.

[0088]

[0089]

[0090] As shown in Table 6, the activities of α-amylase and β-amylase in the stem sheath after heading first increased and then decreased with the growth process. Compared with conventional irrigation, the light dry-wet quantitative irrigation treatment significantly enhanced the activities of α-amylase and β-amylase in the stem sheath at each test period, promoted the reactivation of starch stored in the stem sheath before heading, and provided sufficient material basis for grain filling.

[0091] Table 7. Effects of light dry and wet quantitative irrigation on the activities of granule-bound starch synthase (GBSS) and starch branching enzyme (SBE) in post-flowering grains of different rice varieties.

[0092]

[0093]

[0094] As shown in Table 7, the activities of GBSS and SBE in the grain first increased and then decreased with the growth process. Compared with conventional irrigation, light dry and wet quantitative irrigation significantly enhanced the activities of the two enzymes, promoted starch synthesis in the grain, and allowed more photosynthetic products to be converted into starch and stored in the grain.

[0095] Table 8. Effects of light dry and wet quantitative irrigation on non-structural carbohydrates (NSCs) of different rice varieties

[0096]

[0097] As shown in Table 8, at the end of the vegetative growth period, the total accumulation of NSCs in the stems under the light-dry-wet quantitative irrigation treatment was higher than that under conventional irrigation. During the grain-filling period, the stem-sheath NSC translocation amount (ΔNSCs), NSC translocation rate, and NSC contribution to yield under the light-dry-wet quantitative irrigation treatment were on average 124.16%, 105.94%, and 105.72% higher than those under the conventional irrigation treatment, respectively.

[0098] Table 9. Effects of light dry and wet quantitative irrigation on grain weight and grain filling rate of different rice varieties.

[0099]

[0100]

[0101] As can be seen from Table 9, light dry and wet quantitative irrigation can shorten the time for grains to reach the maximum filling rate, maintain filling intensity, promote grain filling, and increase grain weight.

[0102] Example 2: Effects of different soil drying rates after heading on yields of different panicle types (indica and japonica rice)

[0103] 1. Tested varieties and cultivation conditions

[0104] Same as Example 1.

[0105] 2. Irrigation treatment

[0106] A three-factor experiment was conducted, considering irrigation method, rice variety, and rice panicle type. Irrigation method (A) was the main area, rice variety (B) was the main sub-area, and rice panicle type (C) was the secondary sub-area. Lightly dry and quantitatively irrigated at water potentials of 0 kPa, -5 kPa, -10 kPa, -15 kPa, -20 kPa, and -25 kPa were implemented after rice heading. The field was divided into six main areas, two main sub-areas, and three secondary sub-areas, totaling 36 plots. Each plot was 5 × 6 m in size, separated by 1 m wide ditches. A plastic film was inserted 0.5 m deep into the soil to form a barrier.

[0107] 3. Sampling and Determination

[0108] At maturity (one day before harvest), 10 rice plants from each plot were sampled to determine yield components. The actual harvested area was 5m². 2 Production was measured using the same method as in Example 1, and the results are shown in Table 10.

[0109] Table 10 Rice yield corresponding to different water drop potentials applied during the heading stage.

[0110]

[0111]

[0112] Different letters a, b, and c indicate significant differences at the P=0.05 level, comparing different desiccation potentials of the same variety.

[0113] As shown in Table 10, when the soil moisture potential during the heading stage is above -15 kPa, it has a certain yield-increasing effect, but the effect is not significant. When the moisture potential is below -15 kPa, it causes severe drought stress to rice, affecting the normal growth and development of rice roots, resulting in poor yield increase or even yield reduction. When the soil moisture potential is around -15 kPa, it promotes the translocation of assimilates to grains, thereby promoting grain filling, increasing the harvest index, and ultimately achieving the best yield increase effect.

Claims

1. A highly efficient irrigation method for promoting grain filling by regulating the greening trait of rice, characterized in that, The method determines whether rice plants exhibit chlorosis based on leaf color thresholds. For rice plants exhibiting chlorosis, soil water potential indices for suitable soil drying levels at each growth stage are determined based on rice variety, panicle size, and leaf age patterns. A light, shallow-water-drying quantitative irrigation process is then implemented, where water is naturally allowed to dry from a shallow water layer to a specified soil water potential before being re-irrigated to a shallow water layer. This cycle continues until harvest. The rice varieties include indica and japonica varieties, and the panicle types include large, medium, and small panicles. The efficient irrigation method includes the following steps: (1) From transplanting to the 4th leaf stage, i.e. from transplanting to the beginning of tillering: maintain a shallow water layer of 2-3 cm in the field; (2) The 4th leaf stage to the N-nth leaf stage, that is, the leaf age stage at the beginning of tillering to the critical leaf age stage for effective tillering, where N = total number of leaves on the main stem and n = number of elongated internodes: the soil naturally dries from a water level of 2-3 cm. Depending on the rice variety, when the water potential is -10 kPa to -3 kPa, irrigate to a shallow water layer of 2-3 cm, and then let it dry naturally again. This cycle is repeated. No irrigation is allowed in the field before the soil water potential reaches the above-mentioned index value. (3) The N-n leaf stage to the N-n+3 leaf stage, that is, the critical leaf age for effective tillering to the leaf age at the beginning of jointing: let the water naturally dry from the groundwater layer of 2-3cm. Depending on the rice variety, when the water potential is -12KPa to -5KPa, irrigate to a shallow water layer of 2-3cm, and then let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value. (4) From the N-n+3 leaf stage to the 4th leaf stage, that is, from the leaf age at the beginning of jointing to the leaf age at the beginning of panicle differentiation: let the water naturally dry from the groundwater layer of 2-3cm. Depending on the rice variety, when the water potential is -10KPa to -3KPa, irrigate to a shallow water layer of 2-3cm, and then let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value. (5) The 4-3.1 leaf stage from the bottom, i.e. the bud differentiation stage, the 3.0-2.1 leaf stage from the bottom, i.e. the branch differentiation stage, and the 2.0-0.8 leaf stage from the bottom, i.e. the spikelet differentiation stage: let the water naturally dry from the 2-3 cm water level. Depending on the rice variety, when the water potential is -12KPa to -5KPa, irrigate again to a water level of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value. (6) The 0.7-0 leaf stage, i.e. the pollen mother cell formation and meiosis stage: let the water dry naturally from the 2-3 cm water level. Depending on the rice variety, when the water potential is -15KPa to -7KPa, irrigate to a shallow water layer of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value. (7) From the 0-leaf stage to 45 days after heading and from 45 days after heading to harvest: let the water naturally dry from the 2-3 cm water level. Depending on the rice variety, when the water level drops to -15 KPa to -12 KPa, irrigate to a water level of 2-3 cm, and let it dry naturally again. Repeat this cycle. Do not irrigate the field before the soil water potential reaches the above-mentioned index value.

2. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (2), the different drying potentials of rice varieties are -10KPa to -3KPa. Specifically, for indica rice varieties, the drying potential is -5KPa for large-spike varieties, -7.5KPa for medium-spike varieties, and -10KPa for small-spike varieties; for japonica rice varieties, the drying potential is -3KPa for large-spike varieties, -5KPa for medium-spike varieties, and -7KPa for small-spike varieties.

3. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (3), the different drying potentials of rice varieties are -12KPa to -5KPa. Specifically, for indica rice varieties, the drying potential is -7.5KPa for large-spike varieties, -10KPa for medium-spike varieties, and -12KPa for small-spike varieties; for japonica rice varieties, the drying potential is -5KPa for large-spike varieties, -7KPa for medium-spike varieties, and -10KPa for small-spike varieties.

4. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (4), the different drying water potentials of rice varieties are -10KPa to -3KPa. Specifically, for indica rice varieties, the drying water potential is -10KPa for large-spike varieties, -7.5KPa for medium-spike varieties, and -5KPa for small-spike varieties; for japonica rice varieties, the drying water potential is -7KPa for large-spike varieties, -5KPa for medium-spike varieties, and -3KPa for small-spike varieties.

5. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (5), the 4th to 3.1th leaf stage (bract differentiation stage) has a different drying potential for rice varieties ranging from -12 kPa to -5 kPa. Specifically, for indica rice varieties, the drying potential is -12 kPa for large-panicle varieties, -9 kPa for medium-panicle varieties, and -7.5 kPa for small-panicle varieties; for japonica rice varieties, the drying potential is -10 kPa for large-panicle varieties, -7 kPa for medium-panicle varieties, and -5 kPa for small-panicle varieties. a; The 3.0~2.1 leaf stage mentioned above is the branch differentiation stage. The drying water potential for different rice varieties is -12KPa~-5KPa. Specifically, for indica rice varieties, the drying water potential is -12KPa for large-panicle varieties, -9KPa for medium-panicle varieties, and -7.5KPa for small-panicle varieties; for japonica rice varieties, the drying water potential is -10KPa for large-panicle varieties, -7KPa for medium-panicle varieties, and -5KPa for small-panicle varieties.

6. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (5), the 2.0 to 0.8 leaf stage refers to the spikelet differentiation stage. The drying potential of different rice varieties is -12KPa to -5KPa. Specifically, for indica rice varieties, the drying potential is -8KPa for large-spike varieties, -10KPa for medium-spike varieties, and -12KPa for small-spike varieties; for japonica rice varieties, the drying potential is -5KPa for large-spike varieties, -7KPa for medium-spike varieties, and -10KPa for small-spike varieties.

7. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (6), the different drying water potentials of the rice varieties are -15KPa to -7KPa. Specifically, for indica rice varieties, the drying water potential is -10KPa for large-spike varieties, -12KPa for medium-spike varieties, and -15KPa for small-spike varieties; for japonica rice varieties, the drying water potential is -7KPa for large-spike varieties, -10KPa for medium-spike varieties, and -12KPa for small-spike varieties.

8. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (7), from the 0-leaf stage to 45 days after heading, the drying potential of different rice varieties is -15KPa to -12KPa. Specifically, for indica rice varieties, the drying potential is -15KPa for large-panicle varieties, -15KPa for medium-panicle varieties, and -15KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -12KPa for large-panicle varieties, -12KPa for medium-panicle varieties, and -12KPa for small-panicle varieties.

9. The efficient irrigation method for promoting grain filling by regulating the greening trait of rice according to claim 1, characterized in that: In step (7), from 45 days after heading to harvest, the drying potential of different rice varieties is -15KPa to -12KPa. Specifically, for indica rice varieties, the drying potential is -15KPa for large-panicle varieties, -15KPa for medium-panicle varieties, and -15KPa for small-panicle varieties; for japonica rice varieties, the drying potential is -12KPa for large-panicle varieties, -12KPa for medium-panicle varieties, and -12KPa for small-panicle varieties.

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