Abstract
Incorporation of crop straw into the soil along with inorganic fertilization is a widespread agricultural practice and is essential in nutrient-scarce soils, such as iron-rich (ferruginous) paddy soils. The responses of soil bacterial communities to straw incorporation under different nitrogen inputs in iron-rich soils remain unclear. Therefore, 6000 kg ha−1 dry wheat (Triticum aestivum L. cv. Zhengmai 12) straw was applied to a rice paddy with and without nitrogen amendment (0, 80, 300, and 450 kg ha−1 N as urea), to investigate its effects on soil fertility and bacterial community structure. Organic matter, total nitrogen, and water contents tended to decrease in straw-incorporated soils with different nitrogen inputs. Proteobacteria was the dominant bacterial phylum across all treatments (26.3–32.5% of total sequences), followed by Chloroflexi, Acidobacteria, and Nitrospirae. Up to 18.0% of all the taxa in the bacterial communities were associated with iron cycling. Straw incorporation with nitrogen amendment increased the relative abundance of iron oxidizers, Gallionellaceae, while decreasing the relative abundance of iron reducers, Geobacteraceae. Bacterial community composition shifted in different treatments, with total nitrogen, water, and Fe(III) contents being the key drivers. Straw incorporation supplemented by 300 kg ha−1 N increased bacterial richness and enhanced all the predicted bacterial functions, so that it is recommended as the optimal nitrogen dosage in practice.
Highlights
Straw application is a widespread agronomic practice in developed countries [1,2].in China, burning and discarding still account for a large fraction of the disposed straw under an annual straw productivity of 900 million tons [3]
Straw incorporation supplemented by 300 kg ha−1 N increased bacterial richness and enhanced all the predicted bacterial functions, so that it is recommended as the optimal nitrogen dosage in practice
The relative abundances of dominant bacterial phyla, including Proteobacteria, Chloroflexi, Acidobacteria, Nitrospirae, and Actinobacteria, were all negatively correlated with soil TN, total phosphorus phosphorus (TP), Fe(II), and water content (WC) contents
Summary
Straw application is a widespread agronomic practice in developed countries [1,2]. In China, burning and discarding still account for a large fraction of the disposed straw under an annual straw productivity of 900 million tons [3]. Such improper agronomic practices have led to nutrient losses [4] and to environmental challenges. Previous studies have reported that long-term straw application enhances carbon (C) sequestration considerably, by 50–100%, in China’s subtropical paddy soils [11,12]. According to Potthoff et al [13], applying straw could increase soil microbial C, and, in turn, soil C stocks, which are already relatively high in Chinese croplands [14,15]
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