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Article

Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability

by
Juan Hu
1,2,†,
Xianjiao Guan
1,2,†,
Xihuan Liang
1,2,
Binqiang Wang
3,
Xianmao Chen
1,2,
Xiaolin He
4,
Jiang Xie
1,2,
Guoqiang Deng
1,2,
Ji Chen
5,
Xiuxiu Li
1,2,
Caifei Qiu
1,2,
Yinfei Qian
1,2,
Chunrui Peng
1,2,
Kun Zhang
3,* and
Jin Chen
1,2,*
1
Key Laboratory of Crop Ecophysiology and Farming System for the Middle and Lower Reaches of the Yangtze River, Ministry of Agriculture and Rural Affairs, Key Laboratory of Arable Land Improvement and Quality Improvement of Jiangxi Province, National Engineering and Technology Research Center for Red Soil Improvement, National Agricultural Experimental Station for Agricultural Environment of Yichun, Soil and Fertilizer & Resources and Environment Institute, Jiangxi Academy of Agricultural Sciences, Nanchang 330200, China
2
Jinggangshan Institute of Red Soil, Jinggangshan Branch of Jiangxi Academy of Agricultural Sciences, Ji’an 343016, China
3
Institute of Red Soil and Germplasm Resources, Nanchang 330000, China
4
Jiangxi Agricultural Technology Extension Station, Nanchang 330046, China
5
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agriculture 2024, 14(7), 1168; https://doi.org/10.3390/agriculture14071168
Submission received: 2 July 2024 / Revised: 13 July 2024 / Accepted: 15 July 2024 / Published: 17 July 2024
(This article belongs to the Section Crop Production)
Browse Figures
Versions Notes

Abstract

:
Straw returning has gradually been adopted as an effective approach to address the serious degradation of farmland. However, the carbon/nitrogen (C/N) ratio of rice straw is generally too high for microorganisms to decompose the organic materials and release nutrients, which may minimize the benefits of straw returning to the agricultural production system. This study aimed to investigate the effects of straw returning on rice production and propose optimum nitrogen (N) management for early rice production under a straw returning system. The total N fertilizer that was evaluated was 165 kg N ha-1, urea (46% N), applied in different proportions in three stages of rice cultivation: basal, tillering, and panicle. Using no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment (T1) as the control, four different N fertilizer ratios of basal:tillering:panicle, including 5:2:3 (T2), 5:2:2 (T3), 5:4:1 (T4), and 5:5:0 (T5) were set under straw returning. The return of straw decreased the available N in the soil at the tillering stage, and impeded root growth and the crop canopy from establishing, which decreased the effective panicles by 10.1% compared with that of T1, limiting the increases in rice grain yield. Increasing the N fertilizer ratio 10–20% (T3 and T4) at the tillering stage effectively increased the content of soil ammonium and nitrate nitrogen, improved the root growth, and increased the root activities by 16.0–40.5% at the tillering stage. As a result, the effective panicle number increased by 5.1–16.2%. Among these, T4 treatment maximized the benefits of straw returning the most. Additionally, increasing the N fertilizer ratio at the tillering stage increased the shoot uptake across the early rice growing season and synchronized crop N uptake with the accumulation of carbon assimilates, which enhanced the crop growth rate and increased the rice yield by 13.5–25.1%. It is concluded that increasing the N fertilizer ratio by 20% at the tillering stage is a promising strategy to increase the availability of N in the phases of high demand for this nutrient.

1. Introduction

Rice is a staple food for humanity, with great social and economic importance. The demand for rice continues to grow with the rapidly expanding population. The south of the Yangtze River, as the major double rice-growing region, produces about one-third of the total rice in China [1]. Thus, it is of great significance to ensure the high-yielding and sustainable production of rice in this region. However, the degradation of paddy soil in this region is increasing under intensive agriculture, which greatly restricts crop production [2,3].
Crop straws, as one of the main by-products of agricultural production, are important carbon-rich energy sources, containing abundant organic and mineral nutrients that are necessary for crop growth and development [4,5]. China is one of the top agricultural-producing countries, with annual straw production ranking first in the world. According to statistics, the total amount of straw in China in 2022 was 9.77 × 108 t. Therefore, using crop straws appropriately and efficiently plays a crucial role in environmentally friendly, efficient, and sustainable agricultural production. Crop straw is a high-quality organic matter, which can be used as a resource to fertilize the soil [6,7,8]. It has been proven that straw returning was able to ensure progressive increase in carbon sequestered in the soil over time, improving the soil quality, biodiversity, functioning, and also contributing significantly to adaptation and mitigation of climate change [9,10,11]. Additionally, crop residue contains abundant nitrogen, phosphorus, and potassium nutrients. Generally, the amounts of N, P, and K in rice straw at harvest are 5–8, 0.7–1.2, and 12–17 kg, respectively, per ton of straw on a dry weight basis [12,13]. Therefore, straw returning theoretically can offset part of the P2O5, K2O, and N fertilizers consumption [3]. Reducing the N rate by 20% with straw returning significantly improved the soil structure and no significant losses of maize grain yield were observed [14]. Encouraged by national policies, straw returning has been widely recognized and accepted as a crucial farmland management measure to improve soil fertility and crop yields [10]. The most significant increases in rice yield were obtained in the northeast region, while less pronounced yield improvements were observed in regions at low latitudes, compared to those at higher latitudes [15]. However, as the decomposition processes of crop straw are complicated and affected by a lot of factors, straw returning can also have some negative impacts on crop growth and the agricultural ecological environment [16,17]. For some nutrient-deprived soils, excessive application of nitrogen fertilizer is relatively common, which generally diminishes both microbial biomass and activity, exacerbates soil acidification and disrupts soil nutrient equilibrium [18,19]. In such circumstances, incorporating straw back into the soil will further exacerbate nutrient imbalances and adversely affect crop growth [20,21,22,23]. Additionally, due to the C/N ratio of crop straw being much higher than the appropriate C/N ratio for soil microorganisms to decompose organic materials, soil N is heavily utilized by microorganisms for straw degradation, leading to native soil N and from fertilizer N immobilization, thereby decreasing the crop yield [24,25,26,27,28]. With varying climate and soil texture factors, straw return could also have negative effects on soil organic carbon (SOC) sequestration [15,29]. In some counties of the northeast China, SOC continues to be lost due to excessively high initial SOC levels [15]. Thus, inappropriate straw returning may deteriorate soil structure and increase nutrient loss, further inhibiting crop production [17,30].
Rice straws are rich in lignins, tannins, and waxes; such substances are difficult for microorganisms to decompose, restricting the nutrition-releasing processes. Additionally, the C/N ratio of rice straw is about 60~100:1, and is rich in carbon, which causes the competition for N between microorganisms and crop plants, especially at the early growth stage, adversely affecting crop growth. The C/N ratio is the key factor determining the N mineralization rate of straws during the early stage of straw decomposition [31]. Some studies have suggested that increasing the N rate could promote the degradation of straws, enhancing the soil N contents, labile organic carbon components, and microbial ecological functions [10,32,33,34]. Appropriately increasing the basal topdressing N ratio with straw returning could effectively alleviate the competition between microorganisms and rice crops, significantly increasing the richness and diversity of soil bacteria, and the N fertilizer utilization efficiency of crops, thus the grain yield [35]. Undoubtedly, optimizing N management is an effective way to maximize the advantages and minimize the disadvantages of straw returning to the crop production system [36]. However, how to optimize the N management strategies and what the underlying mechanisms are still need further study. This study innovatively explored the connections between nitrogen content, root growth, and crop N uptake, putting forward a new optimum nitrogen management to match up the soil nitrogen supply with crop requirements, which addressed a very current research issue regarding sustainable nitrogen fertilization. Based on the fact that the N fertilizer ratio of basal:tillering:panicle = 5:2:3 is widely recognized as the optimum N management strategy under a no straw returning system, the optimum N fertilizer ratio at the tillering stage under a straw returning system should be higher, concerning the competitive effects for nitrogen between microorganisms and rice crops at the early growth stage. To verify this hypothesis, we conducted an experiment with an increasing N fertilizer ratio at the tillering stage in the early rice growth season from 2017 to 2022 in a double-rice cropping system with the following main objectives: (1) to investigate the effects of various N ratios in the early growth stage of rice on the soil nutrients; (2) to explore the impacts of various N ratios in the early growth stage of rice on root growth and activities; (3) to elucidate whether optimizing the N ratio in the early growth stage of rice can match up the crop N uptake with the plant N requirement for growth, thus enhancing crop yields.

2. Materials and Methods

2.1. Experimental Set-Up

This field experiment was conducted across the early rice growing season from 2017 in Jinxian County, Jiangxi province, China (116°20′24″ E, 28°15′30″ N). The hybrid of Xiangzaoxian45 was planted in a density of 25×104 hill ha−1. The trail was arranged in a randomized complete block design with three replicates. The area of each plot was 6 m × 8 m. Five treatments were set up including no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment (T1), straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment (T2), straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:3:2 treatment (T3), straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:4:1 treatment (T4), and straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:5:0 treatment (T5), using T1 as the control. The total N was applied at 165 kg N ha−1 as urea (46% N). In total, 75 kg P2O5 ha−1 was applied as calcium magnesium phosphate (15.0% P2O5) prior to seeding, and 75 kg K2O ha−1 as potassium chloride (60% K2O) were applied equally at basal and panicle initiation stages. The soil types were acrisols. Before the establishment of the experiment platform, the soil organic matter was 20.50 g kg−1, TN was 1.03 g kg−1, total P was 0.43 g kg−1, available N was 127.21 mg kg−1, available P was 7.88 mg kg−1, available K was 5.97 g kg−1, and the buck density was 1.06g cm−3. The data used in this manuscript was obtained in 2021 and 2022. The details are described in Table 1.

2.2. Measurements

2.2.1. Rice Yield and Yield Components

At maturity, six hills from each plot were randomly sampled to determine the yield and yield components according to Liao et al. [37]. The rice kernel was determined with 14% moisture content.
Yield (kg ha−1) = Effective panicles (ha−1) × Spikelets (per panicle) × 1000-kernel weight (g 1000−1 kernels) × 10−6.

2.2.2. The Content of Soil Ammonium N and Nitrate N

The soil samples were collected from the surface layer of 0–20 cm, using a 5-point sampling method. The fresh soil sample was passed through a 2 mm sieve and then preserved at −80 °C in the freezer for later measurement of soil nitrate N and ammonium N according to the method described by Rock et al. [38]. A total of2 mol/L KCl was used to extract 5 g fresh soil for 60 min. Then, the supernatants were collected and analyzed by AA3 continuous-flow analysis (AutoAnalyzer 3, Bran + Luebbe GmbH, Norderstedt, Germany).

2.2.3. Rice Root Characteristics

Rice roots were sampled at tillering, heading, and maturation stages following the same approach as Huang et al. [39]. Each plot was replicated three times. The root activities were determined using methylene blue solution. The length, surface area, and volume of roots were determined using a scanner (Epson Expression 12000XL, Shanghai Zequan Technology Co., Ltd., Shanghai, China) and a WinRHIZO Root Analyzer System (Regent Instruments Inc., Québec City, QC, Canada). Then, the root samples were oven-dried at 105 °C for 30 min and then at 70 °C to a constant weight to determine root biomass.

2.2.4. The N Uptake of Rice Aboveground Biomass

The plant was digested using the H2SO4-H2O2 method for determining plant total nitrogen. Then, the plant N concentration (mg N g−1 DW) was determined by the micro Kjeldahl method [40], and then N uptake of aboveground biomass was calculated according to the equation as follows:
The N uptake of aboveground biomass = plant N concentration in plants × aboveground biomass dry weight. Three plants per plot were sampled as one replicate for the measurement, and each treatment was replicated three times.

2.2.5. Rice Crop Biomass Accumulation and Translocation

Three plants of rice were sampled from each plot at the tillering, heading stage, and maturation stages. Above-ground plant samples were separated into the leaf, stem, and spikelet (from the heading). The plant samples were oven-dried at 75°C to a constant weight and then weighed separately. The proportion of crop biomass in panicles was calculated. The crop growth rate (CGR) was calculated by the equation of CGR (g m−2 d−1) = (W2 − W1)/(t2 − t1), where W1 and W2 are the above-ground biomass (g m−2) measured at the time t1 and t2, respectively [41].

2.3. Data Analysis

Microsoft Excel 2016 (Microsoft, Redmond, WA, USA) and SigmaPlot 12.5 (Systat Software, Inc., Richmond, CA, USA) were used for data processing and plotting, IBM SPSS Statistics 25.0 (IBM Corporation, Armonk, NY, USA) was used for data statistics and analysis. Comparisons among groups were tested by one-way ANOVA and LSD tests at a 0.05 probability level.

3. Results

3.1. Rice Grain Yield

Straw returning slightly increased the spikelets per panicle, but decreased the effective panicle number, leading to no obvious increases in the grain yield of rice compared with no straw returning treatments. Increasing the N fertilizer ratio at the tillering stage with straw returning could increase the effective panicle number of rice, and keep the stability of seed setting rate and 1000-grain weight, thus enhancing the spikelets number and the grain yield. Among these, increasing the N fertilizer ratio of basal:tillering:panicle from 5:2:3 to 5:4:1 increased the yield the most. The grain yield of the T4 (with N applied in the proportion of 5:4:1, respectively, in the basal:tillering:panicle phases) treatment increased by 24.1% (p < 0.05) and 25.1% (p < 0.05), respectively, in 2021 and 2022 compared with that of the T2 (with N applied in the proportion of 5:2:3, respectively, in the basal:tillering:panicle phases) treatment (Table 2). These results suggest that straw returning may reduce the soil available nitrogen content at the tillering stage, which affects the rice yield formation. In contrast, increasing the nitrogen ration at the tillering stage could offset the negative effects of straw returning on rice yield.

3.2. Rice Biomass Accumulation and Translocation

Straw returning significantly increased the crop biomass of rice at the heading and maturation stages but decreased it at the tillering stage. Increasing the N fertilizer ratio at the tillering stage with straw returning increased the crop growth rate across the rice growing season, thus increasing the total crop biomass accumulation. Among these, the crop biomass increased mostly in T4 treatment (with N applied in the proportion of 5:4:1, respectively, in basal:tillering:panicle phases), which significantly (p < 0.05) increased by 14.14%, 19.52%, and 15.71%, respectively, compared with that of T2 (with N applied in the proportion of 5:2:3, respectively, in basal:tillering:panicle phases). Additionally, increasing N fertilizer ratio at the tillering stage with straw returning promoted the crop biomass translocation to panicles. The proportion of crop biomass in panicles of T4 (5:4:1) treatment was significantly increased by 5.35% (p < 0.05), on average, compared with that of T2 (5:2:3) (Figure 1). These results suggest that an insufficient supply of nitrogen at the tillering stage may adversely affect the rice shoot establishment and function, thus decreasing the carbon assimilation and translocation processes.

3.3. Rice N Uptake

Straw returning decreased the crop N uptake at the tillering stage, however, straw returning promoted the N translocation to panicles. Increasing the N fertilizer ratio at the tillering stage significantly enhanced the N uptake rate of rice shoots at the tillering and heading stage, and increased the shoot N content across the rice growing season. Furthermore, it promoted N translocation to panicles. Among these, the T4 (5:4:1) treatment increased the most. The N content of T4 (5:4:1) treatment at tillering, heading, and maturation stages increased by 14.53%, 8.96%, and 6.19% (p < 0.05), respectively, on average compared with T2 (5:2:3). The proportions of N in panicles of the T4 (5:4:1) treatment were increased by 6.90% (p < 0.05) compared with that of T2 (5:2:3) treatment (Figure 2). These results suggest that properly adjusting nitrogen management could optimize the nitrogen uptake and translocation of rice under a straw returning system.

3.4. Rice Root Weigh and Root Characteristics

Straw returning decreased the root growth rate of rice in the early growth stages, affecting the rice root architecture significantly. At the tillering stage, the dry matter weight, length, surface area, and volume of the roots were significantly (p < 0.05) decreased in the T2 (5:2:3) treatment, compared with that of the T1 (5:2:3) treatment. These results suggest that rice root establishment was impeded by the insufficient supply of nitrogen. Increasing the N fertilizer ratio at the tillering stage improved the root growth significantly (p < 0.05). The root dry matter weight, length, surface area, volume, and active absorption area at the tillering stage of T4 (5:4:1) treatment were 17.6%, 15.4%, 17.3%, 14.6%, and 40.5% higher than that of T2 (5:2:3) (Figure 3).

3.5. Soil Nitrate and Ammonium Nitrogen Content

Straw returning significantly decreased the content of soil ammonium and nitrate N at the rice tillering stage. For example, the content of ammonium and nitrate N at the tillering stage in T2 (5:2:3) treatment of 2021 and 2022 decreased on average by 11.25% and 11.16% (p < 0.05), compared with that of T1 (5:2:3). This may because the microorganisms competed for the available N in the soil to decompose straw. Increasing the N fertilizer ratio at the tillering stage could not only increase the soil N content at the tillering stage but also maintain a relatively high level at the later growth stages. Among these, the content of soil ammonium and nitrate N in T4 (5:4:1) treatments increased the most, which were 19.29% and 28.91% (p < 0.05) higher at the rice tillering stage, respectively, compared with that of T2 (5:2:3) treatment (Figure 4).

3.6. Relationships among Rice Yield, Root Characteristics, and Soil Available Nitrogen

Correlation analysis showed that the rice yield and yield components were mainly determined by the root characteristics, nitrogen uptake, and crop biomass. The root characteristics including root volume, root surface area, and root active area at the tillering stage were mainly correlated with the effective panicle number and yield. Meanwhile, the root characteristics, nitrogen uptake, and crop biomass at heading and maturation stages were significantly correlated with the grain yield suggesting that root establishment was crucial for rice yield formation. Additionally, the root characteristics, nitrogen uptake, and crop biomass were closely correlated with the soil available nitrogen (Figure 5).

4. Discussion

4.1. Increasing the N Fertilizer Ratio at the Rice Tillering Stage with Straw Returning Increased the Grain Yields of Rice

Among rice yield components, effective panicle number and spikelet number per panicle have great potential for increase. Due to their large variability and adjustability, many agronomy measures have been adapted to enhance the effective panicle number and spikelet number per panicle for a higher grain yield in rice production [42,43,44,45]. In this study, straw returning increased the spikelet setting rate, enhancing the spikelet number per panicle. This may because of a higher supply of available N around the heading stage, which ensured sufficient nutrition for kernel growth and development as reported in Li et al. [8]. However, straw returning reduced the effective panicle number, which offset the increase in the spikelet number per panicle. Thus, no significant increase in grain yield was observed in the T2 (5:2:3) treatment, compared with that of T1 (5:2:3) (Table 2). Consistently, previous studies have suggested that straw returning might inhibit the rice seedling growth, offsetting the benefits of straw returning on increasing yield or even reducing the rice yield slightly [11]. As straw decomposition at the early stages consumed the nitrogen from the soil, the soil available nitrogen for rice growth decreased. This could be the reason for the negative effects of straw returning on rice seedling growth. It could also be proven by the results that increasing the N fertilizer ratio of basal:tillering:panicle from 5:2:3 to 5:4:1 could significantly increase the panicle number and spikelet number per panicle synchronously, therefore, effectively increasing the grain yield of early rice. However, further increasing the N fertilizer ratio at the tillering stage reduced the effective panicle number and rice yield. Thus, only increasing the tillering fertilizer ratio properly could maximize the benefits of straw returning to obtain a high grain yield. Our results support the idea that increasing the N ratio in the early growth stages of rice is an effective approach to obtaining a higher grain yield in a straw-returning agricultural system.

4.2. Increasing the N Fertilizer Ratio at the Tillering Stage with Straw Returning Synchronized the Soil Available Nutrients and Crop Demand

Synchronizing the supply of soil available N and the demand of rice plants is the key for achieving high grain yield under a straw returning agricultural system. The C/N ratio of rich straw is too high for microorganisms to decompose, causing the competition for soil available N between crop roots and microorganisms, which results in insufficient N application for root growth [8,26]. Consistently, in this study, rice straw returning significantly decreased the contents of ammonium and nitrate N at the rice tillering stage. The tillering stage is a crucial stage to establish a robust root system, ensuring effective acquisition of soil available nutrition and the formation of a high-yielding canopy structure [39,46,47]. Correlation analysis results showed that the effectively panicle number was largely determined by the root volume and root active area at the tillering stage. The reduced soil available N supply at the tillering stage inhibited root growth, resulting in the significant reductions of root length, root surface area, and root volume, which may account for the decreases in the effective panicle number of T2 (5:2:3). The addition of N fertilizer could alleviate the negative effects of straw returning by supplying the soil with available N to weaken the nutrition competition [13,48]. In this study, increasing the N fertilizer ratio at tillering from 20% to 40% significantly increased the length, surface area, active absorption area, and volume of roots at the tillering stage and maintained a relatively high level at the later growth stages. Roots, serving as the primary interface between plants and their soil environment, are responsible for the absorption of water and nutrients from the soil, which are essential for plant growth and development [45,49,50]. Straw returning with an increasing N ratio at the tillering stage, not only increased the available soil N at the tillering stage but also ensured a higher N supply at the panicle stage, which created a healthy and highly efficient root system. Accordingly, the N uptake rate was increased across the rice growth season, especially at the tillering and panicle stages.

5. Conclusions

Straw returning might cause competition for N between crops and microorganisms, resulting in insufficient available soil N for rice plant growth, offsetting some of the benefits of straw returning on crop production. Increasing the N fertilizer ratio 20% (with N applied in the proportion of 5:4:1, respectively, in the basal:tillering:panicle phases) at tillering ratio with straw returning effectively increased the availability of soil N at the tillering stage, and ensured sufficient N supply at rice later growth stages, which promoted robust root establishment and rice growth, thus gaining more effective panicles and rice grain yield.
After conducting the research, we noticed that there existed a research gap in nitrogen management to match up the soil nitrogen supply with the rice demanding in consideration with various soil texture, straw management, climate conditions, cropping patterns, and such factors that affect the “supply–demand” relationship. Therefore, researchers should focus on closing this research gap. The variations in rice straw management measures undoubtedly changed the nitrogen “supply–demand” relationship in the cropping system, which call for new optimum nitrogen management for rice production. The agricultural policy-makers should combine the actual situation of agricultural production and scientific studies to guide farmers in agricultural management. In this study, we found that straw returning reduced the nitrogen supply for rice growth at the early stages, thus decreased the effective panicle number. Therefore, we suggest that the policy-makers should encourage farmers to properly increase the nitrogen rate at the rice early growth stage, thus ensuring effective tillers and panicle number, maximizing the benefit of straw returning on rice production.

Author Contributions

Conceptualization, K.Z. and J.C. (Jin Chen); Software, J.H., X.G. and X.L. (Xihuan Liang); Validation, X.L. (Xihuan Liang), B.W., X.C., X.H., J.X., G.D., J.C. (Ji Chen), X.L. (Xiuxiu Li) and C.Q.; Formal analysis, B.W., X.C., X.H., J.X., G.D., J.C. (Ji Chen), X.L. (Xiuxiu Li) and C.Q.; Investigation, C.Q., K.Z. and J.C. (Jin Chen); Data curation, B.W., X.C., X.H., J.X., G.D., J.C. (Ji Chen) and X.L. (Xiuxiu Li); Writing–original draft, J.H., X.G. and X.L. (Xihuan Liang); Writing–review and editing, Y.Q., C.P., K.Z. and J.C. (Jin Chen); Funding acquisition, K.Z. and J.C. (Jin Chen). All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by the National Nature Science Funds (32060431; 32360530); The Science and Technology Special Grant for Jinggangshan Agricultural Hi-Tech Zone (20222-051246); Basic research and talent training special project of Jiangxi Academy of Agricultural Science (JXSNKYJCRC202426); National Key Research and Development Program of China (2016YFD0300901); Jiangxi Province Key Laboratory of Arable Land Improvement and Quality Enhancement (2024SSY04221); Danish Independent Research Foundation (1127-00015B).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The data presented in this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors report no conflicts of interest.

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Agriculture 14 01168 g001
Figure 1. Effects of increasing N fertilizer ratio at the rice tillering stage on crop biomass accumulation and translocation. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. P1: The periods during the seedling to tillering stage. P2: The periods during the tillering to heading stage. P3: The periods during the heading to maturation stage. Values followed by a different small letter are significantly different at 5% probability level. The same as follow.
Figure 1. Effects of increasing N fertilizer ratio at the rice tillering stage on crop biomass accumulation and translocation. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. P1: The periods during the seedling to tillering stage. P2: The periods during the tillering to heading stage. P3: The periods during the heading to maturation stage. Values followed by a different small letter are significantly different at 5% probability level. The same as follow.
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Figure 2. Effects of increasing N fertilizer ratio at tillering stage on the rice N uptake and translocation of rice. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. P1: The periods during the seedling to tillering stage. P2: The periods during the tillering to heading stage. P3: The periods during the heading to maturation stage. Values followed by a different small letter are significantly different at 5% probability level.
Figure 2. Effects of increasing N fertilizer ratio at tillering stage on the rice N uptake and translocation of rice. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. P1: The periods during the seedling to tillering stage. P2: The periods during the tillering to heading stage. P3: The periods during the heading to maturation stage. Values followed by a different small letter are significantly different at 5% probability level.
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Figure 3. Effects of increasing N fertilizer ratio at the tillering stage on rice root characteristics. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. Values followed by a different small letter are significantly different at the 5% probability level.
Figure 3. Effects of increasing N fertilizer ratio at the tillering stage on rice root characteristics. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:5:0 treatment. Values followed by a different small letter are significantly different at the 5% probability level.
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Figure 4. Effects of increasing N fertilizer ratio at the rice tillering stage on the soil available N content. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal: tillering: panicle = 5:5:0 treatment. Values followed by a different small letter are significantly different at the 5% probability level.
Figure 4. Effects of increasing N fertilizer ratio at the rice tillering stage on the soil available N content. Note: T1 (5:2:3), no straw returning with the N fertilizer ratio of basal:tillering:panicle = 5:2:3 treatment. T2 (5:2:3), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:2:3 treatment. T3 (5:3:2), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:3:2 treatment. T4 (5:4:1), straw returning with four different N fertilizer ratios of basal:tillering:panicle = 5:4:1 treatment. T5 (5:5:0), straw returning with four different N fertilizer ratios of basal: tillering: panicle = 5:5:0 treatment. Values followed by a different small letter are significantly different at the 5% probability level.
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Figure 5. Person correlation analysis. Note: * Significant at the 0.05 probability level. ** Significant at the 0.01 probability level; RDW: root dry matter weight, RL: root length, RV: root volume, RSA: root surface area, RAA: root active area, NP: nitrogen uptake, CB: crop biomass; EPN: effective panicle number, SN: spikelet number, GY: rice grain yield.
Figure 5. Person correlation analysis. Note: * Significant at the 0.05 probability level. ** Significant at the 0.01 probability level; RDW: root dry matter weight, RL: root length, RV: root volume, RSA: root surface area, RAA: root active area, NP: nitrogen uptake, CB: crop biomass; EPN: effective panicle number, SN: spikelet number, GY: rice grain yield.
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Table 1. Details of the experimental design and the dose of N applied in three phases to a rice crop.
Table 1. Details of the experimental design and the dose of N applied in three phases to a rice crop.
TreatmentsStraw Returning or NotThe N Rate (kg ha−1)
Basal FertilizerTillering
Fertilizer		Panicle
Fertillzizer
T1No straw returning82.533.049.5
T2Straw returning82.533.049.5
T382.549.533.0
T482.566.016.5
T582.582.50.0
Table 2. The effects of increasing the tillering fertilization ratio on rice yield.
Table 2. The effects of increasing the tillering fertilization ratio on rice yield.
YearTreatmentsEffective Panicle Number (104 ha−1)Cofficient of VariationSpikelet Number/PanicleCofficient of VariationSeed Setting Rate (%)Cofficient of Variation1000-Grain Weight (g)Cofficient of VariationGrain Yield (t ha−1)Cofficient of Variation
2021T1 (5:2:3) *302.75 b0.031 84.28 b0.022 88.87 a0.004 25.37 a0.012 6.68 c0.019
T2 (5:2:3)275.00 c0.030 93.14 ab0.015 90.78 a0.002 25.72 a0.011 6.95 c0.001
T3 (5:3:2)302.75 b0.016 97.80 a0.013 90.75 a0.001 25.50 a0.017 7.96 b0.012
T4 (5:4:1)319.42 a0.040 101.90 a0.018 91.75 a0.004 24.86 a0.011 8.62 a0.010
T5 (5:5:0)283.67 c0.059 87.69 b0.032 89.48 a0.004 25.13 a0.006 6.49 c0.007
2022T1 (5:2:3)294.44 b0.008 80.10 c0.012 75.83 b0.012 24.30 a0.013 5.05 c0.023
T2 (5:2:3)272.22 b0.018 94.28 b0.007 82.07 a0.010 24.18 a0.006 5.92 bc0.006
T3 (5:3:2)286.11 b0.044 96.32 b0.005 86.86 a0.008 24.15 a0.015 6.72 b0.020
T4 (5:3:2)308.33 a0.071 101.45 a0.016 85.18 a0.034 23.83 a0.009 7.40 a0.076
T5 (5:3:2)275.00 b0.030 95.43 b0.019 74.17 b0.011 23.77 a0.000 5.38 c0.036
* Proportion of nitrogen fertilization applied at doses of 165 kg N ha−1, in the phases at basal:tillering:panicle, respectively. Means within the column followed by different letters are significantly different by the LSD test (p < 0.05).
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Hu, J.; Guan, X.; Liang, X.; Wang, B.; Chen, X.; He, X.; Xie, J.; Deng, G.; Chen, J.; Li, X.; et al. Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability. Agriculture 2024, 14, 1168. https://doi.org/10.3390/agriculture14071168

AMA Style

Hu J, Guan X, Liang X, Wang B, Chen X, He X, Xie J, Deng G, Chen J, Li X, et al. Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability. Agriculture. 2024; 14(7):1168. https://doi.org/10.3390/agriculture14071168

Chicago/Turabian Style

Hu, Juan, Xianjiao Guan, Xihuan Liang, Binqiang Wang, Xianmao Chen, Xiaolin He, Jiang Xie, Guoqiang Deng, Ji Chen, Xiuxiu Li, and et al. 2024. "Optimizing the Nitrogen Fertilizer Management to Maximize the Benefit of Straw Returning on Early Rice Yield by Modulating Soil N Availability" Agriculture 14, no. 7: 1168. https://doi.org/10.3390/agriculture14071168

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