Tillage and Irrigation Requirements of Sorghum (<i>Sorghum bicolor</i> L.) at Hamelmalo, Anseba Region of Eritrea

Abstract

Most Eritrean farmers do not adopt soil conservation measures and till even sloppy fields 2 - 4 times for planting sorghum (Sorghum bicolor L.) with a view to facilitate rainwater intake. Field experiments were conducted at Hamelmalo to optimize tillage and irrigation requirements of sorghum in loamy sand. Tillage treatments were conventional tillage (4 times) on existing slopes (CTf), conventional tillage on managed plots (terraced) with residue (CTm + R) and without residue (CTm &#45 R), reduced tillage (single tillage 4 days after heavy rainfall) on managed plots with residue (RTm + R) and without residue (RTm &#45 R) and no tillage (direct planting) on managed plots with residue (NTm + R) and without residue (NTm &#45 R) randomized in four replications. Tillage in CTm and CTf was same. Experiment was repeated in year II along with a new experiment in split plot design with same tillage treatments in main plots and 4 irrigation treatments in subplots in 3 replications. Irrigation treatments were rainfed (I0), 70 mm irrigation at 50% depletion of soil moisture in CTm &#45 R from 1 m profile after end of monsoon (I1), 70 mm irrigation 7 days after irrigation in I1 (I2), and 70 mm irrigation 7 days after irrigation in I2 (I3). Bulk density increased and infiltration rates decreased by harvesting due to tillage but changes were lower in residue plots of NT and RT than CT. Optimum soil moisture for emergence of sorghum was within 0.145 ± 0.002 m3 m-3 at which soil strength was well below critical level for root growth. Soil strength in tilled layer due to intermittent wetting and drying following planting exceeded 2000 k Pa when dried below 0.143 m3 m-3 moisture. Soil profile in CTf did not recharge by rainfall even by end of the rainy season, whereas it was fully wetted in level and terraced plots. Conservation measures resulted 80 - 150 mm of residual moisture per 2 m of soil profile at sorghum harvesting. Residual moisture was relatively more in residue and irrigated plots than in nonresidue and CTf plots. Soil bunding and levelling alone raised sorghum yields in RT + R to 2887 kg ha-1 under rainfed and 3980 kg ha-1 under 70 mm irrigation 21 days after last rainfall of the season (I1). Corresponding yields in CTf were 501 kg ha-1 under rainfed and 1161 kg ha-1 under irrigation. Single preplanting tillage 4 days after heavy rainfall (RT) was as good as 2 - 4 tillage (CT) practiced by farmers. Sorghum yields in Hamelmalo could be about 2752 kg ha-1 by water use of 344 mm and 4009 kg ha-1 by 432 mm. Water use in CTf was lowest (208 mm) under rainfed.