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Effect of Tillage Time, Tilth and Evaporativity on Water Conservation by Soil Mulch

Congress: 2008
Author(s): Shirahatti Shashidhar
Full contact address of corresponding author: Dr. S. S. Shirahatti, Assoc. Prof. of SWE, College of Agricultural Engineering, Raichur-584 102 Karnataka, India. Phone: ++91-08532-220440, Fax: ++91-08532-220079 E-mail: s_shirahatti@hotmail.com

Keyword(s): water conservation technologies, soil mulch, conservation tillage, evaporativity
Abstract1. Proposed title: Effect of Tillage Time, Tilth and Evaporativity on Water Conservation by Soil Mulch 2. Full name of the authors: S.S. Shirahatti (Mr.) 3. Full contact address of corresponding author: Dr. S. S. Shirahatti, Assoc. Prof. of SWE, College of Agricultural Engineering, Raichur -584 102 Karnataka, India. Phone: ++91-08532-220440, Fax: ++91-08532-220079 E-mail: s_shirahatti@hotmail.com Preferred mode of presentation: Oral 4. Theme : 6 .Water Conservation and Demand Management Sub theme : Water Reuse and Conservation Technologies ABSTRACT Introduction Tillage accelerates the formation of a loose dry layer at the surface, which differs from the undisturbed soil below in its water transmission and thermal properties. The extent of water conservation by tillage induced soil mulch depends upon the time of creation of soil mulch and other factors that determine the time trends in the rate of water loss from the soil, the soil texture and the structure achieved in the mulching process. The rate of vapour loss through the mulch is known to depend upon the properties of the mulch and the potential evaporation. Objective The effects of four times of tillage and four types of tilth, viz., coarse, medium, fine and very fine in sandy loom and silty clay loam soils and under low and high evaporativity on water conservation were studied using Mortonís CRAE model. Methods Tillage was done at the soil water contents between 0.30 to 0.11 cm3 cm-3 in the upper 5 cm in silty clay loam and 0.25 and 0.09 cm3 cm-3 in sandy loam soils in Ludhiana, India. In the low evaporativity period, the potential evaporation (PE) fluctuated between 0.5 to 3.6 mm and averaged at 2 mm/ day. During the high evaporativity period, PE ranged from 3.3 mm/day in the beginning to 15.9 mm/day towards the end and averaged at 9.8 mm/day. The study period considered was 65 to 67 days under low and 51 and 52 days under high evaporativity. Mortonís CRAE model was examined with respect to its application for estimating short term area evaporation amounts from field-sized areas. The assessment focused on the procedures used in the model to evaluate different parameters and on comparisons of evaporation by CRAE with values derived from a soil water balance applied to field observation the hydro meteorological and soil moisture data used in the comparison. A vapour transfer coefficient based on the aerodynamic equation for wind correction as introduced into CRAE was adopted to determine whether closer agreement exists between modelled and measured estimates. Results In case of evaporation reduction by tillage, compared with untilled soil, evaporation averaged across tilth was 28 per cent less with first three times of tillage and 12 per cent less with fourth time. The maximum water conservation with the first, second, third and fourth times of tillage averaged 6.9, 14.8, 2.6 and 0.8 mm in silty clay and 18.7, 10.5, 2.8 and 1.3mm in the sandy loam respectively. Coarse and medium tilths appeared more effective with the earliest and finer tilths with subsequent times of tillage under high evaporativity. Conclusions To attain maximum water conservation under high evaporativity, it would be necessary to avoid very fine tilth with the early and coarse tilth with the delayed tillage. Lower water conservation with very fine tilth in the earliest tillage suggested that fine clods at the surface permitted greater liquid flow than the coarse clods, when the soil was wet and the evaporativity was high. For tillage with pulverizing implements, a moderate delay in the time of tillage after wetting of the soil may be desirable from the point of water conservation in the silty clay loam soil. Tillage resulted in sharp increase in water content at the interface of the tilled and untilled layers which suggests a break in capillarity. Water content below the soil mulch was higher and nearly constant with depth under low evaporativity. In untilled soil, water content increased gradually with depth. Under high evaporativity, drying of the soil was more intense and the untilled soil below the mulch lost more water. The water content for the first time of tillage and untilled soils were almost identical. This leads to the conclusion that the stirring of the wet soil under high evaporativity is likely to partially reestablish the capillarity which seems to be responsible for less water conservation by the earliest tillage in silty clay loam soils. Incorporating a wind correction factor into the model improved the estimation of regional evaporation.
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