Minimal irrigation on small agricultural watersheds with red soils in the semi-arid tropics of Andhra Pradesh, India
Abstract Part of the runoff water from sloping red soils of the Andhra Pradesh region was stored and used for local irrigation of several crops over several years, during which rainfall varied widely in the cropping period. This type of utilisation of harvested water is unique in the semi-arid tropics. Judicious application of small amounts of water through alternate central furrows to wet the root zone during a stress period increased yields significantly. Response to irrigation decreased with increasing soil moisture in the root zone. Irrigation was beneficial in both sub-normal and normal rainfall conditions during the cropping period. With above normal rainfall there was hardly any need for irrigation. According to rainfall probability, expected yield increases of sorghum and castorbean over time were on average 251 and 523 kg/ha with irrigation of only 15 and 50 mm, respectively. With only 20 mm of irrigation in a cropping cycle consisting of pigeonpea/pearl millet-cowpea or horsegram, gross yields increased significantly. Vegetables, hitherto grown under open well irrigation only, were irrigated using pond water. Vegetable yields increased significantly with irrigation. A ground cover of pulses to prevent soil erosion during post-monsoon storms could be maintained with minimal irrigation still giving some fodder yield.
Effect of deep tillage on dryland crop production in red soils of India
Abstract The red soils of the semi-arid tropics of Andhra Pradesh, India, are shallow, eroded and compact. The profile is anisotropic with a dense sub-surface layer. The average depth of the surface layer is 8.2 cm. The solum depth varies from 50 to 100 cm. The subsurface layer restricts the root proliferation of crops. A light wooden country plow is used by farmers for primary tillage. It penetrates on average to a depth of 15.5 cm with a coefficient of variation of 80%. To disturb the sub-surface layer to a greater extent a heavy-duty disc plow was used. This tilled to a depth of 23.3 cm, with a coefficient of variation of 29%, and reduced the bulk density. The infiltration and depth of penetration of the wetting front increased considerably with deep tillage. The advantage of deep tillage to crop yields was found to be dependent on rainfall pattern and plant type. The interaction was between recharge in the profile and rooting depth. In a normal rainfall season the yield advantage was observed for both short duration (sorghum and pearl millet) and long duration (castor) crops, while the advantage in an above-normal rainfall season was restricted to long duration crops only. No yield advantage was noticed in a sub-normal rainfall year for any of the crops. The residual effects of deep tillage were marginal. Therefore, by considering the historical rainfall data, it was observed that deep tillage was beneficial in 63 and 91% of years for short and long duration crops, respectively. Adoption of deep tillage every year in traditional castor—sorghum rotation resulted in benefits in 56% of years for both the crops. Since deep tillage requires a high monetary input, it is advisable to adopt this practice only for castor. This illustrates clearly the need for considering rainfall pattern and crop requirements to select an appropriate tillage practice under rainfed farming.
Laminar heat or mass transfer in rectangular channels and in cylindrical tubes for fully developed flow: comparison of solutions obtained for various boundary conditions
Abstract A comparison is made of results obtained with various boundary conditions at the wall of the channels. By comparing blood Sherwood numbers for finite wall resistance with those for constant concentration boundary condition only a small variation is found for various points along the blood channel.