R.K. Tomar

Pedotransfer functions for predicting the hydraulic properties of Indian soils

Most of the data pertaining to Indian soils are limited to the major soil separates, sand, silt, and clay. We examined the possibilities of using these parameters to describe the hydraulic characteristics of the soils of India. The final or steady-state infiltration rate, which is mainly profile-controlled, showed a power function relationship with the maximum and the average clay content in the soil profile. The saturated hydraulic conductivity also showed a similar relationship with the silt + clay content. The soil water content at a given suction could be satisfactorily predicted using the percentage of major soil separates, sand, silt, and clay. The coefficients in the soil water function ψ(θ) were linearly related to the sand content. Non-linear regression equations were developed to predict these coefficients using the percentages of sand and clay in soils. The equations proved to be quite satisfactory for a wide range of textures and provided reasonably accurate estimates of the soil water characteristic curve from a minimum of readily available data.

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.

Impact of Tillage and Residue Management on Water and Thermal Regimes of a Sandy Loam Soil under Pigeonpea-Wheat Cropping System

Tillage and crop residue management are the most critical components of the cultivation, which significantly affect the soil-plant-water relations. Conservation tillage (CT) aims to improve soil condition and conserve soil water, although limited information is available on seasonal variation of soil water and temperature under cropping systems. A medium duration (6 years) experiment with different tillage and residue management option on a sandy loam soil in pigeonpea-wheat cropping system was selected to monitor the changes in soil structure through adoption of conservation agriculture (CA), and the subsequent impact on soil water and thermal regimes over the growing period of wheat crop. Treatments were: conventional tillage with incorporation of previous crop residue (CT+R); conventional tillage with residue removal (CT-R); no-tillage with residue retained over surface as mulch (NT+R); and no-tillage with residue removed (NT-R). The impact was quantified in terms of change in basic soil physical parameters viz., bulk density (BD), penetration resistance (as Cone Index, CI) and porosity, and their effect on soil water dynamics, and seasonal and diurnal soil temperature. At the initial growth stages (9 to 51 DAS), NT+R and NT-R recorded 5–10 per cent higher BD at 0–10 cm layer, but was comparable with CT+R and CT-R at the later stages. Soil pore ( 30 μm) and meso-(5–30 μm) pore volumes had marginal differences. A sub-surface (10–20 cm) hard layer (CI 1.7–1.9 MPa) was omnipresent, although omission of tillage resulted in marginal reduction in CI at this layer. Marginally higher macro-pores in NT systems caused higher initial rate of infiltration and the cumulative infiltration. Throughout the growing season of wheat, NT+R retained higher soil water than other tillage-residue combinations [17% (0 to 48), 11% (−5 to 32), and 14% (−2 to 36), higher compared to NT-R, CT+R and CT-R]. Soil water content in NT+R was also higher by 20% (−5 to 41) before irrigation cycles. Similarly, soil temperature was the most regular in NT+R, even at 3 cm depth due to the presence of surface residue and higher amount of soil water. The difference between temperatures at 10 am and 3: 30 pm was 2.9 (0.2–6.3)°C in NT+R, compared to 3.8 (0.2–7)°C in NT-R, 4 (0.8–8)°C in CT+R, and 3.1 (0.7–5.5)°C in CT-R. Therefore, role of tillage and crop residues in modifying soil physical environment and maintaining better soil water and thermal conditions have been clearly documented.