The inhibition of the net CO2 assimilation (A) during photosynthesis is one of the major physiological effects of both nitrogen (N) and potassium (K) deficiencies on rice growth. Whether the reduction in A arises from a limitation in either the diffusion and biochemical fixation of CO2 or photochemical energy conversion is still debated in relation to N and K deficiencies. In this study, the gas exchange parameters of rice under different N and K levels were evaluated and limitations within the photosynthetic carbon capture process were quantified. A was increased by 17.3 and 12.1% for the supply of N and K, respectively. The suitable N/K ratio should be maintained from 1.42 to 1.50. The limitation results indicated that A is primarily limited by the biochemical process. The stomatal conductance (LS), mesophyll conductance (LM), and biochemical (LB) limitations were regulated by 26.6–79.9, 24.4–54.1, and 44.1–75.2%, respectively, with the N and K supply.
Quantity–intensity curves were used to evaluate the dynamics of soil potassium (K) at different soil depths under different K management. The equilibrium concentration ratio of K (CR0) increased with increasing K concentration. K fertilization and straw return increased soil K supplying capacity by increasing CR0, non-specific available K (-∆K0) and equilibrium K (CK0). The CR0 increase 107%, 392% and 577% at the 0–20 cm layer and 55%, 102% and 131% at the 20–40 cm layer, respectively, under K fertilization, straw return and the interaction of them. The CK0 and -∆K0 at the 0–20 cm layer significantly increased after K fertilization and straw return. The labile K varied from 0.11 to 0.19 cmol kg−1, contributed 85.3% to 107.6% of NH4OAc extracted K. Soil K potential buffering capacity showed significant differences in soil depths, while little difference was observed under different K management. Th e exchangeable K was meaningless for guiding K application when minimum exchangeable K took up 85.9% to 99.0% of equilibrium exchangeable K. Our results showed K fertilization and straw return was the optimal management to enhance soil K supplying capacity, especially at the 0–20 cm layer.Abbreviations N: nitrogen; P: phosphorus; K: potassium; RS: straw; Q/I: quantity/intensity; CR0: equilibrium concentration ratio of K; KL: labile K; non-specifically available K: -∆K0; PBCK: potential buffering capacity; EK0: equilibrium exchangeable K; CK0: equilibrium solution K; α: magnitude of conversion of added K to exchangeable pool; β: conversion of added K to non-exchangeable K pool; Emin: minimum exchangeable K.
Abstract Sclerotinia stem rot (SSR) is a major fungal disease of oilseed rape ( Brassica napus L.) that causes severe yield losses. Nutrient management is crucial for protecting crops against SSR. Two‐yr field trials combined four levels of N application (0, 90, 180, and 270 kg N ha −1 ) and four levels of K application (0, 60, 120, and 180 kg ha −1 K 2 O) to investigate their interaction effects on SSR disease incidence and seed yield loss caused by SSR. Compared to the sole application of N, the combined application of N and K decreased the SSR disease incidence by 9.9–24.4 and 17.4–37.9% in 2016–2017 and 2018–2019, respectively. N application increased the severity of SSR only at lower K application rates (0 and 60 kg ha −1 K 2 O). Additionally, compared to the sole application of N, the co‐application of N and K dramatically decreased the total yield loss rate (TYLR), by 31.1–60.9 and 19.2–60.3% in 2016–2017 and 2018–2019, respectively. The seed yield response to N uptake was dependent on the level of K application. However, SSR disease dramatically decreased the nutrients use efficiency. Nitrogen and K supply showed synergistic interaction effects on N and K recovery efficiency. These results emphasized the importance of N and K co‐application on reducing the yield loss caused by SSR infection. For a stabilized seed yield, an adequate N (180 kg ha −1 ) application rate combined with a slightly high K application rate (120–180 kg ha −1 ) represents a feasible nutrient management strategy for oilseed rape against SSR disease.
Abstract Optimal potassium (K) fertilization is beneficial for oilseed‐rape ( Brassica napus L.) yield and quality. However, the discrepancy between the high K demand of winter oilseed rape and low soil fertility and insufficient potassium input has limited the sustainable development of oilseed‐rape production. A series of on‐farm experiments in the key winter oilseed‐rape domains of China was conducted from 2004 to 2010 to evaluate K‐fertilizer management for winter oilseed rape. Currently, the average NH 4 OAc‐extractable K content in the 0–20 cm soil layer is 89.1 mg kg –1 indicative of “slight deficiency”. In addition, farmers in China usually fail to use sufficient K fertilizer in oilseed‐rape production, the average mineral‐potassium‐fertilizer input in 2010 being only 35 kg K ha –1 , far lower than the recommended rate of potassium for winter oilseed rape. Adequate potassium fertilization significantly raises seed yield. The average yield‐increase rate for the major production regions due to K‐fertilizer application was 18.5%, and the average K fertilizer–use efficiency 36.1%. Based on the negative correlation between yield response to potassium fertilization and available soil K content, a soil‐K‐test index was established for winter oilseed rape with a threshold value for NH 4 OAc‐extractable soil K of 135 mg kg –1 . When available soil K‐content is below this threshold value, more K fertilizer should be applied to achieve high seed yield and to increase soil fertility. The major challenge for K‐fertilizer management in winter oilseed‐rape production in China will be to guide farmers in the different regions in making reasonable use of K fertilizer through soil K‐testing technology in order to maintain both seed yield and soil fertility.
Cultivation of winter oilseed rape hybrids has been introduced as a promising solution to improve the nitrogen use efficiency (NUE) and to reduce the large N balance surpluses in this crop. To achieve a better understanding of the underlying physiological mechanisms, field experiments were conducted over two years to investigate the dynamics of growth and N capture in an oilseed rape hybrid and its parental lines under both low (0 kg ha−1) and high (180 kg ha−1) N supply. The results showed that the dynamic trajectories of crop growth and N capture could be accurately characterized by logistic equation using growing degree days as the independent variable. At both N rates, the oilseed rape hybrid outperformed the parental lines in seed yield and aboveground biomass accumulation, which was more closely associated with the longer duration (td) of the rapid growth period (RGP), than with the higher maximum growth rate (vm). N uptake was the main factor driving genotypic variation in seed yield, with an increasing importance of N utilization efficiency at high N supply. The hybrid had significantly higher N uptake than the parental lines at both low and high N supply, because of larger vm for N accumulation during the RGP, which may present a scope for genetically improving NUE in oilseed rape. High N application enhanced crop biomass production and N accumulation, as a result of prolonged td and larger vm during the RGP. The initiation of RGP for N accumulation occurred after overwinter period, which could not be accelerated by high N supply, suggesting rational distribution of N fertilizer with reduced basal dose. However, larger amounts in spring would be beneficial for a better synchronization to crop N demand with lower environmental risks.
The increasing food demands from an expanding population necessitate global efforts to increase crop production and ensure food security. The rate of nitrogen (N) fertilizer application is strongly related to crop yield. However, although the application of N fertilizer significantly increases the number of tillers in rice, late emerging tillers usually produce lower yields compared with early emerging tillers. Understanding the physiological constraints of late emerging rice tillers is critical for further increasing rice grain yields. Two-year field experiments, consisting of four nitrogen fertilizer levels, were conducted in order to study variations in the physiological characteristics of different types of tillers. The results revealed that the contributions of late emerging tillers to population rice grain yields improved with increased N levels. However, spikelets per panicle and the grain filling of late emerging tillers were significantly lower than that of the main stems or early emerging tillers under all N levels. The nitrogen harvest index of late emerging tillers was lower than that of main stems and early emerging tillers, and differences gradually increased under higher N rates. Nutrient source deficiency was a primary factor for the low productivity of late emerging tillers. Additionally, rapid malondialdehyde accumulation and delayed emergence determined the short growth duration of late emerging tillers. Further, low actual photochemistry efficacy (ΦPSII) resulted in insufficient photosynthetic assimilate supply in late emerging tillers, whereas highly constitutive non-photochemical energy dissipation (ΦNO) might damage the photosynthetic system. Moreover, the low activity of SuSase and spikelets per panicle revealed both inadequate sink activities and storage sites. The identification of these limiting factors in late emerging rice tillers will assist in closing the 'yield gap' between late emerging tillers and early emerging tillers, and contribute to further increasing rice grain yields.
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