Soil Physical Quality as Influenced by Long-Term Application of Fertilizers and Manure Under Maize-Wheat System

Soil physical environment as affected by long-term fertilizer experiment application in a maize-wheat system on sandy loam soils of India was characterized and quantified using a unified soil physical quality index (S). Treatments were 100% and 150% of recommended nitrogen, phosphorus, and potassium (NPK); 100% NPK + farmyard manure; 100% NPK + sulfur; and control (no fertilizer or manure). Soil aggregation, bulk density, organic carbon in bulk soil (SOC) and aggregates, pore-size distribution, saturated hydraulic conductivity, field capacity moisture content, and plant-available water content were evaluated. Most of the effects were pronounced in 0- to 15-cm layer. Better aggregation was found with 100% NPK + farmyard manure, where macroaggregates were greater than 50% of total soil mass. Aggregation indices were positively and significantly correlated with SOC in 8- to 4-mm aggregates. Bulk density was significantly lower (1.51 Mg m−3) with manure, corresponding to maximum SOC content (6.8 g kg−1). The field capacity moisture content, plant-available water content, and saturated hydraulic conductivity were significantly higher in manure plots. Transmission and storage pores were more abundant in manure-treated plots. Effects of 150% NPK or 100% NPK + sulfur doses was better compared with 100% NPK, indicating that the recommended dose of NPK was suboptimal to maintain the desired soil physical health. Close associations of S with soil physical parameters was obtained, indicating potential of S in quantifying the modifications of soil physical environment through fertilizer and manure applications.