[Effect of reducing N and regulated fertilization on N loss from wheat-maize rotation system of farmland in Chao soil region of North China Plain]. / 农田减氮调控施肥对华北潮土区小麦-çŽ‰ç±³è½®ä½œä½“ç³»æ°®ç´ æŸå¤±çš„å½±å“.

The application of large amounts of nitrogen (N) fertilizer can result in soil N accumulation and consequently N loss. To address these problems in a wheat-maize rotation area of the North China Plain, a two-year field experiment (2016-2017) was conducted to examine the effects of three different N fertilizer strategies on crop yield, N uptake, N loss and soil inorganic N content. The treatments were: controlled-release fertilizer, microbial fertilizer, nitrification inhibitor and farmer's practice (control). The results showed that the wheat yield from the microbial fertilizer treatment in 2016 was significantly lower than that from the controlled-release fertilizer treatment and the nitrification inhibitor treatment, but was not significantly different from conventional farmer fertilization. The N uptake of wheat and annual crops in the microbial fertilizer treatment was significantly reduced. There was no significant difference in crop yield and N uptake among the treatments in 2017. Soil fertility of the tillage layer was maintained or improved in all three treatments compared with the control, and the contents of alkali-hydrolyzed nitrogen, available potassium and organic matter increased with the increase of plant growth period in the microbial fertilizer treatment. Microbial fertilizer and nitrification inhibitor reduced the inorganic N content in the 40-100 cm soil profile, while controlled-release fertilizer increased the inorganic N content in the 0-40 cm soil layer. N loss through ammonia volatilization was higher than that through leaching, which was greater than the loss through N2O emission. Runoff loss was negligible. Among the treatments, N loss in farmer's practice treatment was the highest. Microbial fertilizer significantly reduced N loss through ammonia volatilization, but the loss through leaching was larger. In conclusion, with reduced N application compared with the farmer's practice, controlled release fertilizer and nitrification inhibitor could maintain crop yield and N uptake, and microbial fertilizer could ensure crop yield and N uptake for a longer plant growth period. The results suggested that inorganic N content in the 40-100 cm soil layer could be reduced in the soil by adding microbial fertilizer and nitrification inhibitors, and the amount of inorganic N was not reduced significantly by application of controlled release fertilizer. Several N reduction measures could reduce N loss. The microbial fertilizer treatment needed to be modified to reduce N leaching.

[Meta-analysis of stable carbon and nitrogen isotopic enrichment factors for aquatic animals].

Isotopic enrichment factor (Δ, the difference between the δ value of food and a consumer tissue) is an important parameter in using stable isotope analysis (SIA) to reconstruct diets, characterize trophic relationships, elucidate patterns of resource allocation, and construct food webs. Isotopic enrichment factor has been considered as a constancy value across a broad range of animals. However, recent studies showed that the isotopic enrichment factor differed among various types of animals although the magnitude of variation was not clear. Here, we conducted a meta-analysis to synthesize and compare Δ13C and Δ15N among four types of aquatic animals (teleosts, crustaceans, reptiles and molluscs). We searched for papers published before 2014 on Web of Science and CNKI using the key words "stable isotope or isotopic fractionation or fractionation factor or isotopic enrichment or trophic enrichment". Forty-two publications that contain 140 studies on Δ13C and 159 studies on Δ15N were obtained. We conducted three parallel meta-analyses by using three types of weights (the reciprocal of variance as weights, the sample size as weights, and equal weights). The results showed that no significant difference in Δ13C among different animal types (teleosts 1.0 per thousand, crustaceans 1.3 per thousand, reptiles 0.5 per thousand, and molluscs 1.5 per thousand), while Δ15N values were significantly different (teleosts 2.4 per thousand, crustaceans 3.6 per thousand, reptiles 1.0 per thousand and molluscs 2.5 per thousand). Our results suggested that the overall mean of Δ13C could be used as a general enrichment factor, but Δ15N should be chosen according to the type of aquatic animals in using SIA to analyze trophic relationships, patterns of resource allocation and food webs.