Abstract
Soil aggregate stability is one of the important physical properties affecting rice (Oryza sativa L.) production and soil sustainability. This study was undertaken to evaluate the influence of different medium-term fertilization regimes on soil aggregate stability and aggregate-associated carbon (C) and nitrogen (N) in rhizosphere and bulk soil. This experiment consisted of three treatments, including mineral fertilizer alone (NPK), mineral fertilizer plus rice straw (NPK + RS), and controlled-release blended fertilizer plus cattle manure (CRF + CM). Although higher fertilizer costs were in the CRF + CM treatments, one-time application could save labor costs compared to the conventional split application of chemical fertilizers. The results showed that, compared to the NPK alone, the combined application of NPK with organic amendments improved the proportion of >0.25 mm macroaggregate, soil organic carbon (SOC), total nitrogen (TN) concentrations, and mean weight diameter (MWD) in both rhizosphere and bulk soil during the whole rice growing season. In rhizosphere, the proportion of macroaggregate was significantly positively (p < 0.01) correlated with root biomass while it had no significant correlation with SOC in the proportion of all sizes of aggregates. By contrast, bulk soil had a significantly (p < 0.01) positive relationship between the proportion of >2 mm class and organic C associated with smaller particle-sized aggregates (0.25–2 mm and <0.25 mm). In addition, the organic C associated with 0.25–2 mm showed the largest contribution of the total SOC content in all treatments during the rice growing stage. Overall, the results suggested that the medium-term application of mineral fertilizer with organic amendments was beneficial to improve soil aggregate stability and C and N accumulation.
Highlights
The organic binding agent can be classified into three main groups on the basis of age and degradation of the organic matter: (1) transient; (2) temporary; and (3) persistent [3,4]
Our studies showed that medium-term application of mineral fertilizer combined
Our studies showed that medium-term application of mineral fertilizer combined with organic manures increased the proportion of macroaggregate (>0.25 mm) in both the rhizosphere and bulk soil (Table 1), which were similar to our previous results obtained on dry sieves [19]
Summary
Soil aggregate stability is an important indicator of soil quality since it influences soil water-holding capacity, biological activity, root penetration, and plant growth [1,2]. Organic matter is the major binding agent which affects aggregate stabilization at different levels. The organic binding agent can be classified into three main groups on the basis of age and degradation of the organic matter: (1) transient (mainly polysaccharides); (2) temporary (roots and hyphae); and (3) persistent (humic materials associated with aluminum and amorphous iron) [3,4]. The persistent organic binding agents play a key role in the forming of 0.25 mm macroaggregates [5]. Soil adjacent to roots might have different physical properties with those of bulk soil [6]
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