Differential species and varietal tolerance to soil acidity in tropical crops and pastures

The differential tolerance to soil acidity of various important food crops and pastures was studied. Many species and crop varieties were screened for acid tolerance and results are given for maize, rice, grain legumes, cassava and some forage species. Maize varieties doing best with a 2 tons/ha lime treatment produced over 3 tons/ha in semi-commercial fields. Traditional rice varieties responded only to 0.4 tons/ha of lime while the semidwarf varieties responded markedly up to 4 tons/ha. A greenhouse method is proposed to test rice varieties for Al tolerance by measuring root growth in nutrient solutions with different Al concentrations, and comparing values for 3 and 30 ppm Al. It is reported that while field beans and soybeans responded up to 6 t/ha of lime, cowpeas only responded significantly to 0.5 tons/ha. For cassava very large differences between cultivar were observed. However, most of them responded visually to lime up to 2 tons/ha and were adversely affected by 6 tons/ha. Foliar mineral content was strongly influenced by liming even at the lowest lime rates. For grasses lime apparently is required primarily as a Ca source with positive results of 150 kg lime/ha and yield depressions can occure already at 1 ton/ha