AMELIORATION OF A HARDSETTING ALFISOL THROUGH DEEP MOLDBOARD PLOWING,GYPSUM APPLICATION AND DOUBLE CROPPING .3. CROP PRODUCTION AND PROFITABILITY

Deep mouldboard ploughing to 0.45 m, gypsum application (5 t ha-1), an d double cropping were evaluated, alone and combined, as ameliorants f or a hardsetting red-brown earth (Alfisol). The double cropped treatme nt consisted of winter wheat (Triticum aestivum) and a summer forage c rop consisting of sudax (Sorghum sudanese) intersown with cowpea (Vign a unguiculata). This paper describes the effect of these treatments on crop development, yield, crop-water relations and economic returns. C rop emergence was not affected by any treatment. Mouldboard ploughing significantly increased wheat grain yield from 1.86 to 2.15 t ha-1, in 1984, but not in 1985. Yield was also increased from 5.18 to 5.68 t h a-1 as a result of gypsum addition in 1985-after no significant differ ence in 1984. Double cropping significantly increased yield (by 0.6 t ha-1) in 1985. Greater increases were obtained with the summer croppin g phase where higher evaporative demand during the summer would have a ggravated soil structural problems associated with hardsetting. Sudax- cowpea dry matter yields were increased from 13.6 to 17 t ha-1 and fro m 13.0 to 17.5 t ha-1 during summer 1984-1985 by gypsum and mouldboard ploughing, respectively. The higher yields are attributed to increase d water storage and depletion, and reduced soil strength for the mould board ploughed and gypsum main treatments. No interactions were found between the main treatments, except at the end of the 1985 winter crop ping phase when there was a negative interaction between mouldboard pl oughing and gypsum application for dry matter, equivalent root length and yield. The yield increases associated with mouldboard ploughing di d not persist beyond the second year of the experiment. Double croppin g combined with mouldboard ploughing (Mb + DC) was the most profitable treatment, whereas mouldboard ploughing with gypsum (Mb + G) was the least profitable for the crops grown in this experiment.