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Drought stress is the key factor limiting soybean yield potential. Soybean seed formation involves a coordinated "subtending leaf-podshell-seed" process, but little is known about the assimilation and transport of photoassimilates in subtending leaves, podshells and seeds or their relationships with soybean seed formation under drought stress. To address these research gaps, two-year experiments with two soybean cultivars, Wandou 37 (drought tolerant) and Zhonghuang 13 (drought sensitive), were conducted under three soil water content (SWC) conditions in 2020 and 2021 based on the responses of their yield to drought. We analyzed the photosynthetic assimilation and translocation of photoassimilates in subtending leaves, podshells and seeds by stable isotope labeling. Compared with those under 75% SWC, 60% SWC and 45% SWC significantly decreased the Wandou 37 seed weight by 19.4% and 37.5%, respectively, and that of Zhonghuang 13 by 26.9% and 48.6%, respectively. Compared with those under 75% SWC, drought stress decreased the net photosynthetic rate and the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SuSy), which in turn decreased the photosynthetic capacity of the subtending leaves. The podshells ensure the input of photoassimilates by increasing the SuSy activity, but the weakened source-sink relationship between podshells and seeds under drought stress leads to a decrease in the translocation of assimilates from podshells to seeds. The lack of assimilates under drought stress is an important factor restricting the development of soybean seeds. We conclude that the decrease in seed weight was caused by the decrease in the photosynthetic capacity of the subtending leaves and the decrease in the overall availability of photoassimilates; moreover, by a decrease in the translocation of assimilates from podshells to seeds.

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Wheat-rice cropping system in China, characterized by smallholder with conventional practice, is energy- and carbon-intensive. Cooperative with scientific practice is a promising practice to increase resource use while reducing environmental impact. However, comprehensive studies of the energy and carbon (C) budgeting of management practices on the actual field-scale production under different production types are lacking. The present research examined the energy and C budgeting of smallholder and cooperative using conventional practice (CP) or scientific practice (SP) at the field scale level in the Yangtze River Plain, China. The SPs and cooperatives exhibited 9.14 % and 6.85 % and 4.68 % and 2.49 % higher grain yields over the corresponding CPs and smallholders, respectively, while maintaining 48.44 % and 28.50 % and 38.81 % and 20.16 % higher net income. Compared to the CPs, the corresponding SPs reduced the total energy input by 10.35 % and 7.88 %, and the energy savings were primarily attributable to reductions in fertilizer, water, and seeds through the use of improved techniques. The total energy input in the cooperatives was 11.53 % and 9.09 % lower than that for the corresponding smallholders due to the mechanistic enhancements and improved operational efficiency. As a result of the increased yields and reduced energy inputs, the SPs and cooperatives ultimately increased energy use efficiency. The high productivity attributed to increased C output in the SPs, which increased C use efficiency and the C sustainability index (CSI) but decreased the C footprint (CF) over the corresponding CPs. The higher productivity and more efficient machinery of cooperatives increased the CSI and reduced the CF compared to the corresponding smallholders. Overall, the SPs coupled with cooperatives were the most energy efficient, C efficient, profitable and productive for wheat-rice cropping systems. In the future, improved fertilization management practices and integration of smallholder farms were effective means for developing sustainable agriculture and promoting environmental safety.

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The combination effects of nitrogen (N) fertilizer and planting density on maize yield, N use efficiency and the characteristics of canopy radiation capture and radiation use efficiency are not well documented in the Huanghuaihai Plain region in China. A 2-year field experiment was conducted from 2017 to 2018 in a split plot design with two N levels (240 and 204 kg N ha-1) applied to main plots and three plant densities (67,500, 77,625 and 87,750 plants ha-1) allocated to sub plots. Our results show that a 30% greater plant density combined with a 15% lower N rate (basal N) enhanced N partial factor productivity (NPFP) by 24.7% and maize grain yield by 6.6% compared with those of the conventional high N rate combined with a low density planting management practice. The yield increase was mainly attributed to significantly increased kernel numbers and biomass. The increased intercepted photosynthetically active radiation (IPAR) was the primary factor responsible for the high productivity of maize at increased planting density under reduced N conditions. The results indicate that increase planting density with reduced basal N application might benefit maize cropping for achieving high yields and sustainable development of agriculture.

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Split application could improve nitrogen (N) uptake and increase sweetpotato yields under reduced N supply; however, little is known about how it affects the process of starch production in storage roots. An experiment was conducted to determine the effects of three N management strategies [conventional basal N management; 80% of the conventional N rate applied as a basal fertilizer; 80% of the conventional N rate equally split at transplanting and 35 days after transplanting] on starch accumulation, enzyme activity and genes expression in the conversion of sucrose to starch and the relationships among them. The results showed that, compared with conventional basal N management, split application decreased sucrose accumulation by 11.78%, but increased starch accumulation by 11.12% through improving the starch accumulation rate under reduced N supply. The ratio of sucrose synthetase to sucrose phosphate synthase, the enzymatic activity of ADP-glucose pyrophosphorylase (AGPP), starch synthase, and the expression of their corresponding genes were promoted by split application under reduced N supply and were positively correlated with starch accumulation rate. AGPP is the rate-limiting enzyme in starch synthesis in storage roots under different N management strategies. These results indicate that starch accumulation was enhanced by split application through regulating the activity and gene expression of key enzymes involved in the conversion of sucrose to starch under reduced N supply.

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The unreasonable resource allocation and lower resource use efficiency for rice-wheat double cropping system in Jianghuai region resulted from climate change severely limit the coordinated development of annually high yield and high efficiency crops. Optimizing seasonal resource allocation through sowing date adjustment is an important way to tap the annual high-yield potential and improve resource use efficiency. To quantify the effects of sowing date of rice and wheat on annual yield and resource allocation and utilization efficiency, field experiments were conducted in 2013-2015. Results showed that compared with the conventional rice-wheat cropping system (T2), the two seasons appropriate late-cast cropping system (T3) could coordinate resource allocation in the two seasons through the sowing date adjustment, and transfer the redundant radiation and heat resources in the wheat season to the rice. The distribution rate of accumulated temperature, radiation and rainfall resources for T3 were: rice season accounted for 60.5%, 46.5% and 56.7%, wheat season accounted for 36.3%, 50.0% and 40.9%, and the ratio between two seasons was 1.67, 0.94 and 1.39, respectively. Rice yield and its proportion of annual production were significantly increased. The wheat yield was significantly decreased, with the variation range being smaller than that of rice. The total annual yield was increased by 336.3 kg·hm-2 as compared with T2. The temperature, radiation and rainfall production efficiency for rice in T3 were increased by 9.8%, 5.6% and 8.3% in compared to T2, respectively. There was no significant difference in the climate resource utilization efficiency of wheat season. The annual resource production efficiency of T3 was increased by 4.8%, 3.1% and 6.0% over the T2, respectively. Earlier (T1) or latest sowing (T4) of two seasons cropping system was not appropriate for annual yield formation and resource utilization. In summary, improving resource utilization efficiency in rice season is the key way to increase annual grain yield potential in Jianghuai region. The results provided theoretical and practical bases for the excavation of yield potential of the regional annual cropping system and the adjustment of planting structure.

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Splitting nitrogen (N) application is beneficial for enhancing sweetpotato growth and promoting optimum yields under reduced N rates; however, studies concerning how split N can affect sweetpotato N dynamics and utilization are limited. Field experiments were conducted from 2015 to 2016 to determine how split N application affects sweetpotato N uptake and N use efficiency (NUE) under a reduced N rate. Two cultivars (Xushu 22 and Shangshu 19) were planted under four N treatments, a conventional basal application of 100 kg N ha-1 (100:0), a basal application of 80 kg N ha-1 (80:0), two equal split applications of 80 kg N ha-1 (basal and 35 days after transplanting, 40:40) and a N omission treatment (N0). Data from two years revealed that sweetpotato yields decreased at a reduced 20% N rate with a basal application (80:0); however, the reduced 20% N rate with a split application (40:40) significantly increased the yield by 16.6-19.0%. Although the 80:0 treatment decreased sweetpotato N uptake, the 40:40 treatment increased the N uptake by increasing the N uptake rate and prolonging the duration of the fast N uptake phase. In comparison to the basal application, the split N application used N more efficiently, showing consistently higher levels of agronomic use efficiency, recovery efficiency, physiological efficiency and partial factor productivity. NUEs under split N improved due to increased N uptake during the middle and late growth stages and a higher N partition ratio to the storage root. The above results indicate that split N application provides better N for crop developmental stages and is recommended as an alternative approach to simultaneously increasing storage root yield and NUE under a reduced N rate in sweetpotato production in China.

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