With the aim of maximizing nitrogen use efficiency (NUE) of wheat in the North China Plain by optimizing irrigation and nitrogen application, a field experiment with a split-plot design was conducted. The main plots were subjected to three irrigation levels: bringing soil water content in the 0–40 cm profile to 65% (I1), 75% (I2) and 85% (I3) of field water capacity. The subplots were subjected to three nitrogen application rates: 150 (N150), 210 (N210) and 270 (N270) kg N ha−1. Compared with the N270, N210 treatment enhanced grain yield, NUE, and net income by 4.5%, 6.2%, and 5.8%, respectively (two-year averages). Additionally, it reduced soil nitrate reductase activity, the abundance of denitrification-related bacteria, and loss rate of fertilizer nitrogen by 12.9%, 53.3%, and 16.3%, respectively. Compared with the N150, N210 treatment increased grain yield, grain nitrogen accumulation, and net income by 15.9%, 14.2%, and 26.3%. Relative to I1 and I3, I2 treatment increased root length density in the 20–60 cm soil layer, uptake rate of fertilizer nitrogen, grain yield, and net income. Overall, the combination of irrigation to 75% of field capacity with nitrogen application at 210 kg N ha−1 increased wheat’s capacity for nitrogen uptake and remobilization and thereby grain nitrogen accumulation, and increased NUE by reducing nitrogen loss rate.
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Improving the nitrogen transport and accumulation of nutrient organs after wheat flowering, as well as improving the nitrogen accumulation characteristics of wheat grains, is beneficial for increasing the nitrogen accumulation and yield of wheat. This study aimed to clarify the physiological mechanisms underlying the differences in nitrogen utilization efficiency among wheat plants at different yield levels, so as to provide a theoretical basis for reducing yield differences and improving nitrogen utilization efficiency and to achieve high yield and efficient production of wheat.
The field experiments were conducted in Shiwang Village, Xiaomeng Town, Shandong Province for two consecutive years from 2020 to 2022. Using Tobacco Farmer 1212 as the planting material, three yield levels of wheat fields with a perennial winter wheat yield of around 10 500 kg·hm-2 (S), 9 000 kg·hm-2 (H), and 7 500 kg·hm-2 (M) were selected to compare and analyze the differences in plant nitrogen accumulation and transport, grain nitrogen accumulation characteristics, and grain yield in wheat fields with different yield levels.
Compared with H and M wheat fields, S wheat field significantly increased the number of spikes per unit area and thousand grain weight, with grain yield 19.64%-27.91% and 51.68%-80.87% higher than H and M wheat fields, respectively, resulting in the highest nitrogen absorption efficiency, nitrogen partial productivity and nitrogen harvest index. The nitrogen accumulation in the nutrient organs of S wheat field during the flowering period increased by 14.22-42.11 kg·hm-2 and 53.74-103.16 kg·hm-2, respectively. The nitrogen accumulation in mature nutrient organs was S, H>M. Compared with H and M wheat fields, S wheat field significantly increased the nitrogen transport of pre flowering nutrient organs and nitrogen accumulation after flowering, and increased the contribution rate of nitrogen accumulation in post flowering nutrient organs to grains, thereby achieving the highest nitrogen accumulation in mature grains. The S wheat field significantly increased the content of free amino acids and soluble proteins in flag leaves after flowering, for promoting the inter source sink transport of nitrogen. According to the logistic equation fitting, the S wheat field significantly increased the maximum and average accumulation rates of grain nitrogen, prolonged the duration of grain nitrogen accumulation, and was the main reason for obtaining the highest grain nitrogen accumulation.
Suitable soil environment in S wheat field could promote the transfer of stored nitrogen from vegetative organs to grain, and increase the rate of grain nitrogen accumulation and prolong the duration of grain nitrogen accumulation, which was the main reason for the highest grain yield and nitrogen use efficiency.
The physiological mechanism of starch accumulation and yield formation of spring maize in black soil under suitable nitrogen application was studied, in order to provide the theoretical basis for high yield and high efficiency cultivation technology of spring maize.
Field experiments were conducted in the spring maize growing seasons of 2022 and 2023 in Gongzhuling City, Jilin Province, Jilin Academy of Agricultural Sciences. Five nitrogen application treatments were set up: no nitrogen (N0), 90 kg·hm-2 (N90), 135 kg·hm-2 (N135),180 kg·hm-2 (N180), and 225 kg·hm-2 (N225). The synthesis capacity of sucrose in the ear leaf and the activity of key enzymes in sucrose metabolism were measured to investigate the sucrose synthesis capacity of the ear leaf and grain starch synthesis capacity under different nitrogen application rates. The accumulation characteristics of total starch and its components in maize grain were fitted by Logistic equation to clarify the impact of nitrogen application rate on the dynamic of starch accumulation in maize grain and grain yield formation.
(1) With the escalation of nitrogen application rates, the yield of spring maize exhibited an initial increase followed by a subsequent decrease. The average yields under N0, N90, N135, N180, and N225 treatments over two years were 8 992.90, 11 199.47, 12 126.78, 14 049.42, and 13 213.21 kg·hm-2, respectively. Notably, the N180 treatment resulted in the highest yield. (2) The sucrose content, sucrose synthetase (SS) and sucrose phosphate synthetase (SPS) activities in ear leaves at 0, 12, 24, 36 and 48 days after flowering under N180 treatment were significantly higher than those under N0, N90 and N135 treatment, and there was no significant difference between N225 and N180 treatment. At 24, 36 and 48 days after flowering, the activity of soluble amylase (SSS) in grains treated under N180 was the highest, and the average SSS activity of grains under N0, N90, N135 and N225 was increased by 62.43%, 31.33%, 14.85% and 7.80%, respectively. (3) Logistic equation analysis showed that the accumulation rate and active accumulation period of total starch, branch chain and amylose in grains of each treatment first increased and then decreased with the increase of nitrogen application amount, and N180 treatment was the best. Compared with N0, N90, N135 and N225 treatments, the two-year average total starch accumulation rate and total starch accumulation active period under N180 treatment were 43.35%, 23.16%, 13.22%, 5.92% and 7.30%, 3.84%, 4.11%, 3.83%, respectively. When the average grain starch accumulation rate reached the maximum in two years, the grain starch accumulation amount was 12.90 g, and the total starch accumulation amount at each treatment maturity stage was 6 725.60, 8 510.17, 9 150.62, 10 387.35 and 9 604.04 kg·hm-2, respectively. (4) Correlation analysis results showed that spring maize yield was significantly positively correlated with sucrose content, sucrose synthase activity, sucrose phosphate synthase activity, soluble starch synthase activity in grains, total starch accumulation, amylopectin accumulation and amylose accumulation in grains at ear position at filling stage. Sucrose content, sucrose synthetase activity, sucrose phosphate synthetase activity and soluble starch synthetase activity in grain were also significantly positively correlated with starch and its component accumulation in grain.
Under the treatment of 180 kg·hm-2 nitrogen application, the spring maize during grain filling exhibited the highest activities of key sucrose metabolism enzymes in the ear sheath leaves, as well as the highest activity of starch synthesis enzymes in the soluble grains. Additionally, it showed the maximum rate of starch accumulation and longest period of active starch accumulation. Furthermore, this treatment resulted in the highest grain yield and starch accumulation, making it the optimal treatment under the experimental conditions.
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Sustainable agriculture in the Huang–Huai–Hai Plain of China is threatened by subsoil compaction and the decline of winter wheat productivity induced by inappropriate tillage regimes. We investigated the effects of optimizing the tillage regime on grain filling and its relationship with flag leaf senescence post-anthesis in winter wheat. Four treatments were compared: rotary tillage, strip rotary tillage, strip rotary tillage with a 2-year subsoiling interval (STS), and conventional plowing tillage. STS produced higher chlorophyll content and leaf area indexes than other treatments, resulting in a greater photosynthetically active radiation capture ratio. The net photosynthesis rate of flag leaves from 14 to 28 days after anthesis and dry matter accumulation at maturity were higher in STS than in other treatments. Sucrose content and sucrose phosphate synthase activity of flag leaves first increased and then decreased during grain filling and were highest in STS. STS increased superoxide dismutase activity, increased soluble protein content, and reduced malondialdehyde concentrations in flag leaves after the middle grain-filling stages, resulting in reduced premature senescence. This consequence extended the active grain filling period and increased grain weight. The highest yields were observed in STS, reaching 10,451 kg ha−1 in 2014–2015 and 10,074 kg ha−1 in 2015–2016, owing to increased spike numbers and 1000-kernel weight. Overall, our study suggested that STS could substantially increase photosynthetic capacity and delay leaf senescence, thus promoting grain filling rate and increasing winter wheat yields.
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