Effects of Straw Return and Feed Addition on the Environment and Nitrogen use Efficiency in the Rice–Crayfish System

Purpose Understanding the direction of nitrogen flow in the rice-crayfish system (RC) and optimizing the rate of nitrogen fertilizer application (ORN) are of great significance for sustainable development of RC. Methods To this end, a field experiment involving straw and feed treatment was conducted to delineate the flow of the nitrogen present in the straw (straw-N) and feed (feed-N). Second, under different feed and straw treatments, we carried out a mesocosm experiment with different rates of 15N-labeled nitrogen fertilizer application to explore the optimal rate under the effects of feed-N and straw-N supply.Results The results showed that at 75 kg N ha-1(75N), 14% and 1.86% of feed-N and 4.3% and 8.78% of straw-N is absorbed by crayfish and rice, respectively. The percentage of feed-N and straw-N lost to the environment was the lowest at 75N, i.e., 84.48% and 86.92%, respectively. Using straw return to the field and feeding as the basic management measures for RC, we observed that the rice yield was the highest under 75N, and the highest nitrogen utilization efficiency (NUE) was 25%, and the highest the percentage of soil storing nitrogen by the fertilizer-derived was 34% (lost to the environment, at least 41%).Conclusions ORN could help in the effective utilization of feed-N and straw-N via a compensation effect, promote the absorption and transport of nitrogen, and ultimately lead to an improvement in NUE in RC.

Pollen Grain Number and Viability Contribute to Variation in Effective Ovule Number Among Oilseed Rape Genotypes

While no significant differences in initial ovule number were found among oilseed rape genotypes, there was a large variation in effective ovule number (EON), which determines the final seeds per silique (SPS), a critical component of yield. In this study, we selected 18 oilseed rape genotypes with contrasting nitrogen utilization efficiency (NUtE) to unravel the main factors responsible for different EON and determine the critical period of EON formation under both a field and a pot experiments from 2016-2018. The high NUtE genotypes displayed significantly higher NUtE by 14.3%, along with greater yield per plant (29.4%) and SPS (21.1%) than the low NUtE genotypes. The greater productivity of the high NUtE genotypes was associated with 44.1% higher pollen grain number, 23.5% greater pollen viability, and 39.3% lower ovule abortion rate, compared to the low NUtE genotypes. In addition, the heart stage was the critical ovule development period for delineating the variability of EON among contrasting NUtE oilseed rape genotypes, when the high NUtE genotypes displayed higher silique net photosynthetic rate, surface area, biomass, and RNA expression levels. Taken together, this study indicated the pollen grain number, pollen viability and ovule abortion rate contributed to the final variation in EON and the heart stage was the critical period of determining the EON differences among contrasting NUtE genotypes. Increasing pollen grain number and pollen viability, and decreasing ovule abortion rate before heart stage should be the prerequisite for breeders to improve yield and NUtE of oilseed rape genotypes.

Application of Bag-Controlled Release Fertilizer Facilitated New Root Formation, Delayed Leaf, and Root Senescence in Peach Trees and Improved Nitrogen Utilization Efficiency

It is very important to promote root growth and delay root and leaf senescence, to improve nitrogen absorption and utilization efficiency, and to improve the storage nutrition level of the tree, so as to improve the fruit quality and yield of peach. In this experiment, we compared and analyzed the effects of traditional fertilization and bag-controlled release fertilizer (BCRF) on the growth of shoots and roots, senescence of leaves and roots, and fruit yield and quality. Moreover, the impacts of BCRF on ammonia volatilization, nitrogen utilization rate, fine root turnover, and plant storage nutrients were also investigated. Compared with conventional fertilizer use, the application of BCRF significantly promoted the shoot growth of young peach trees. Additionally, BCRF delayed leaf senescence and increased root activity in autumn. This increased the storage nutrients of the peach tree. Compared with traditional fertilizer, ammonia volatilization reduced to 54.36% under BCRF application situation. BCRF also promoted the occurrence of fine roots and decreased the annual turnover rate. A 15N tracer test showed that, compared with traditional fertilizer, BCRF nitrogen utilization efficiency increased by 37.73% in peach trees under BCRF treatment significantly. The results from 3 consecutive years showed that the application of BCRF increased the yield of individual plants by 21.35% on average compared to the yield from plants receiving equal amounts of fertilizer applied by spreading (FSA). Thus, BCRF can promote the occurrence of fine roots and decrease the root annual turnover rate in peach trees, and it also improves the utilization efficiency of fertilizer, reduces ammonia volatilization, delays leaf senescence, and enhances storage nutrition, fruit yield, and fruit quality in peach trees.