Long term effect of organic and inorganic amendment on acid soil maize yield and corresponding change in soil characteristics

An experiment was conducted from 1997 to 2000 in Cameroon, on acid soil with low pH (4.63), high Aluminium (Al), low calcium (Ca), low magnesium (Mg), and low phosphorus supply (P), to assess the effectiveness of an acid tolerant maize (Zea mays L.) cultivar compared to the use of organic and inorganic fertilizer to correct soil acidity. The experiment was a 2x2x3x2 factorial in a randomised complete block design with six replications. The factors were: phosphorus rate (0 and 60 kg.ha-1 applied as diammonium phosphate), dolomitic lime rates (0 and 2 tons .ha-1), organic manure (0 and 4 tons.ha-1 of poultry manure, 4 tons.ha-1 of leaves of Senna spectabilis), and maize cultivars (ATP-SR-Y an acid soil tolerant, and Tuxpeño Sequia an acid susceptible). Each replication consisted of 4 blocks of 7 treatments with a local maize (CMS 8501) augmented in each block. On non amended acid soil, maize grain yield of ATP-SR-Y, the soil acidity-tolerant cultivar, was 61% higher than grain yield of Tuxpeño Sequia, the soil acidity susceptible cultivar. Continuous maize cultivation on acid soil without amendment further increase soil acidity. This was evident by a decrease in pH (0.23 unit), Ca (31%) and Mg (36%) and by an increase in AI3+ (20%). The yearly application of 60 kg.ha-1 of P for 3 years did not increase the grain yield of the acidity-tolerant cultivar significantly (7%). The 42% grain yield increase obtained with the soil acidity susceptible cultivar on acid soil was partly attributed to increase in available P (35%) of the soil and to the fact that Tuxpeño sequia was AI3+ susceptible but P use efficient. Soil amendment with sole diamonium phosphate tended to increase soil acidity through increases in AI3+ (8%) and H+ (16%) concentration and a decrease in Ca (30%), Mg (11%) and pH (0.07 unit) Lime application, except in the first year resulted in a significant increase in grain yield of both the tolerant (82%) and the susceptible cultivar (208%). The grain yield increase was associated with a significant decrease in exchangeable AI3+ (43%), H+ (51%), and increase in pH (0.27 unit) CEC (5%), and available Ca (154%) and Mg (481%) contents of the soil planted to both the tolerant and the susceptible cultivar. Manure application (poultry and leaves of senna spectabilis) on acid soil, generally resulted in significant (p>0.05) grain yield increase for both the soil acidity tolerant and susceptible cultivars. Poultry manure was more efficient than senna leaves manure producing on average 38% more grain yield. On plot planted to the tolerant cultivar ATP-SR-Y, poultry manure application led to higher increase than did senna leaves in pH (0.24 vs 0.14 unit) in available plant nutrient Ca, Mg and P and in higher decrease in AI3+ (31% vs 09%). On plot planted to the susceptible cultivars, senna spectabilis as compared to poultry manure resulted in higher increase in pH (0.17 vs 0.03 unit), Mg (29% vs 14%) and in higher decrease in AI3+ (15% vs 2%). The available Ca and P were however, better on plot planted to the tolerant cultivar. It was partially concluded that manure application could in a long run decrease the acidity of the soil: However, compared to lime application, the rate in soil characteristic change was slow, suggesting that soil acidity correction with manure would take longer time than the present three yearly application of 4 tons ha-1 investigated in this study. In general, grain yield increase due to soil acidity correction was more related to the decrease in exchangeable AI3+ (R2 = 0.79**) and increase in Ca+ (R2 = 0.74**), than to pH (R2 = 0.52***). However exchangeable AI3 was the main factor determining pH (R2 = 0.66**). These findings suggested that maize cultivation on acid soil must focus on greater understanding of AI3+, Ca+ and Mg dynamics and their management and that breeding maize for AI3+ tolerant and for an efficient use of Ca and Mg from organic manure application is advisable for the acid soil type of C