Effect of inorganic fertilizer and farmyard manure on soil physical properties, root distribution, and water-use efficiency of soybean in Vertisols of central India

A field experiment was conducted on a Vertisol for three consecutive years (1998–2000) to study the effects of combined use of inorganic fertilizer (NPK) and organic manure (farmyard manure) on soil physical properties, water-use efficiency, root growth and yield of soybean [Glycine max (L.) Merr.] in a soybean–mustard cropping system. Application of 10 Mg farmyard manure and recommended NPK (NPK + FYM) to soybean for three consecutive years improved the organic carbon content of the surface (0–15 cm) soil from an initial value of 4.4 g kg−1 to 6.2 g kg−1 and also increased seed yield and water-use efficiency by 103% and 76%, respectively, over the control. The surface (0–15 cm) soil of the plots receiving both farmyard manure and recommended NPK had larger mean weight diameter (0.50 mm) and a higher percentage of water stable aggregates (55%) than both the inorganically fertilized (NPK) (0.44 mm and 49%) and unfertilized control plots (0.41 mm and 45.4%). The saturated hydraulic conductivity (13.32 × 10−6 m s−1) of the NPK + FYM treatment of the 0–7.5 cm depth was also significantly greater than that of the NPK (10.53 × 10−6 m s−1) and control (8.61 × 10−6 m s−1) treatments. The lowest bulk density (1.18 Mg m−3) in the 0–7.5 cm layer was recorded in NPK + FYM whereas it was highest in the control plots (1.30 Mg m−3). However, at sub-surface (22.5–30 cm) layer, fertilizer and manure application had little effect on bulk density and saturated hydraulic conductivity. Root length density (RLD) up to the 30 cm depth was highest in the NPK + FYM plots and it was 31.9% and 70.5% more than NPK and control plots. The RLD showed a significant and negative correlation (r = −0.88∗∗) with the penetration resistance.