Impact of Subsurface Application of Compound Mineral Fertilizer on Soil Enzymatic Activity under Reduced Tillage

Abstract

Soil biochemical properties shaping soil fertility and agro-ecosystem productivity depend on the reduced tillage system and the dose and method of application of fertilizer; therefore, the research hypothesis put forward proposes that under reduced tillage system conditions, the subsurface application of a multi-component mineral fertilizer would increase soil enzymatic activity, thus favourably influencing the biodiversity of the soil environment. The objective of the three-year study was to evaluate the impact of subsurface application of varying mineral fertilizer rates on soil enzymatic activity under reduced tillage system conditions in soybean, winter wheat and maize rotations. The field experiment was set up as a split-plot design in four replicates. The first experimental factor included two methods of mineral fertilization application: fertilizer broadcast over the soil surface (S); fertilizer applied deep (subsurface placed) using a specially designed cultivator (Sub-S). The other factor was the rates of the mineral fertilizer (NPKS): 85 kg∙ha−1 (F85) and 170 kg∙ha−1 (F170). The method of application and rate of mineral fertilizer did not have a significant effect on the organic carbon and total nitrogen content in the soil of the plots with all rotational crops. Subsurface application of fertilizer significantly increased available phosphorus content in soil under soybean and winter wheat crops; however, it significantly decreased soil pHKCl values within sites with all crops in the rotation compared to surface application. At the same time, deep application of mineral fertilizer significantly stimulated dehydrogenase activity in the soil under the winter wheat crops and acid phosphatase activity in the soil under all rotation crops. The higher level of mineral fertilization contributed to reduction of soil pHKCl under winter wheat and maize, and promoted an increase in the soil P content. Additionally, significant increases of dehydrogenases and urease activity in the soil under winter wheat and maize crops, alkaline phosphatase activity in the soil under all the studied crops, and acid phosphatase activity in the soil under the soybean crops were found, compared to mineral fertilizer in the amount of 85 kg NPKS∙ha−1. The results of the present study have demonstrated a positive effect of subsurface application of compound mineral fertilizer on the soil biochemical parameters in reduced tillage. This may be a recommendation for the subsurface use of multicomponent mineral fertilizers in sustainable agriculture. However, a full objective characterization of the soil environment processes induced by in-depth application of mineral fertilizer in reduced tillage requires long-term monitoring.