Temporal variations in runoff and soil loss in relation to soil conservation practices in catchments in Shiwaliks of lower Himalayas

The soil conservation strategies adopted in the catchments of Shiwaliks, the most fragile region in the Himalayan ecosystem, failed to serve their purpose after a few years of their execution. A study was carried out in four differentially-treated catchments to monitor the variation in runoff and soil loss. The treatments imposed during 1988 included fencing,planting native vegetation and engineering structures in catchment I ; planting native vegetation and fencing in catchment II ; fencing alone in catchment III in addition to an untreated catchment IV. The soil loss during the initial years (1989 – 1995) of imposition of the treatments was lowest (25. 2 t ha-1) in catchment I, treated to the maximum extent and highest (43. 3 t ha -1) in untreated catchment IV. During the later period (1996 – 2006) the trends reversed, i. e., catchment IV recorded the lowest (14. 1 t ha-1) soil loss whereas catchment I recorded the highest (23. 4 t ha-1) soil loss despite the fact that there was no change in the status of soil conservation or the characteristics of the catchments. The runoff was 71 % higher in untreated catchment than in treated catchments initially and this difference decreased to 27% during the later period

A SIMPLE AND PORTABLE RAINFALL SIMULATOR FOR SMALL PLOT STUDIES

The construction details and operating characteristics of a simple and portable rainfall simulator are described. It is suitable for small plot studies of soil erosion by water. Raindrops are formed by blowing air current to a water jet, both at specific intensities. The simulator closely approximates the kinetic energy of natural rainfall. Rainfall intensities ranging form 21 to 97 mm/h can be produced with a median drop diameter renge of 1.1 to 2.6 mm

The effect of rice straw mulch on evapotranspiration, transpiration and soil evaporation of irrigated wheat in Punjab, India

Soil evaporation (Es) is considered to be a non-productive component of evapotranspiration (ET). So, measures which moderate Es may influence the amount of water available for transpiration (T), the productive component of ET. Field experiments investigating the effects of rice straw mulch on components of the water balance of irrigated wheat were conducted during 2006-2007 and 2007-2008 in Punjab, India, on a clay loam soil. Daily Es was measured using mini-lysimeters, and total seasonal ET was estimated as the missing term in the water balance equation. Mulch lowered total Es over the crop growth season by 35 and 40 mm in relatively high and low rainfall years, respectively. Much of this "saved water" was partitioned into T, which increased by 30 and 37 mm in the high and low rainfall years, respectively. As a result, total ET was not affected by mulch in either year. In both years, there was a trend for higher biomass production and grain yield with mulch, but with significant differences only in 2006-2007. Transpiration efficiency (TE) with respect to grain yield was 18.8-19.1 kg ha-1 mm-1 in 2006-2007, and 14.6-16.4 kg ha-1 mm-1 in 2007-2008. While wheat grown in the presence of mulch tended to lower TE, this was only significant in 2007-2008. The results suggest that while mulching of well-irrigated wheat reduces Es, it does not "save" water because the crop compensates by increased T and reduced TE.Zero till Crop factor Mini-lysimeters North-west India

Evaluation of options for increasing yield and water productivity of wheat in Punjab, India using the DSSAT-CSM-CERES-Wheat model

The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004-2005 data and validated with 13 independent data sets from experiments conducted during 2002-2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Yp), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970-1971 to 2005-2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations. Mean Yp across 36 years ranged from 5.2 t ha-1 (10 October sowing) to 6.4 t ha-1 (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.

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