Abstract
A maize pot experiment was conducted to compare the difference of N distribution between bulk and rhizospheric soil after chemical fertilizer with or without soil straw amendment at an equivalent N rate using a 15N cross-labeling technique. Soil N pools, maize N and their 15N abundances were determined during maize growth. The urea plus straw treatment significantly (p < 0.05) increased the recovery of urea N in soil and 26.0% of straw N was assimilated by maize. Compared with urea treatment in bulk soil, urea plus straw treatment significantly (p < 0.05) increased the concentration and percentage of applied N as dissolved organic N (DON) and microbial biomass N (MBN) from milk stage to maturity, increased those as particulate organic N (PON) and mineral associated total N (MTN) throughout maize growth and decreased those as inorganic N (Inorg-N) from the eighth leaf to the silking stage. Compared with bulk soil, rhizospheric soil significantly (p < 0.05) decreased the concentration and percentage of applied N as PON and increased those as Inorg-N and MTN in both applied N treatments from the silking stage, and significantly (p < 0.05) decreased the concentration and percentage of applied N as microbial biomass N (MBN) in the urea plus straw treatment. Overall, straw N was an important N source and combined application of chemical fertilizer with straw increased soil fertility, with the rhizosphere regulating the transformation and supply of different N sources in the soil–crop system.
Highlights
12.0% higher than the U treatment at stage V8, and the opposite trend occurred in shoots, roots, and grains from stages R1 to R6 (Figure 2c,d)
** the U treatment at stage V8, and the opposite trend occurred in shoots, roots, and grains from stages R1 to R6 (Figure 2c,d)
In this equivalent N experiment, urea N immobilization in soil induced by straw and plenty of recalcitrant N in straw [30,45] in the urea plus straw (US) treatment significantly (p < 0.05) decreased shoot or grain biomass (Figure 1a) as well as N accumulation and applied N percentage (Figure 2) from the R1 stage compared with the U treatment
Summary
Long-term uncontrolled chemical fertilizer N application has aggravated soil acidification, groundwater eutrophication, and greenhouse gas emissions [2,3,4]. The combined application of chemical fertilizer and straw at controlled rates may be an efficient method of alleviating these detrimental effects and increasing soil nutrient status [5,6], small amounts of greenhouse gas emissions might be stimulated [7,8,9]. Straw incorporation provides a useful source of N and provides carbon (C) sources for soil microbes, affecting the distribution of N in the crop–soil system [10,11]. Understanding the distribution of chemical fertilizer- and straw-N in crop–soil systems is necessary to evaluate the application of chemical fertilizer combined with straw
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