Use of locally available amendments to improve acid soil properties and maize yield in the Savanna Zone of Mali

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Soil acidity is a major constraint to crop production in the Savanna zone of Mali. The high cost of lime makes it an unrealistic option for resource poor farmers. This thesis addresses the challenges associated with soil acidity management by using locally available materials in three studies. A laboratory study was carried out to investigate the liming potential of the following locally available materials: Cattle manure (CM), sheep manure (SM), goat manure (GM), poultry manure (PM), Sabunjuma compost (SC), maize residue (MS), ash from maize straw (AM), Tilemsi rock phosphate (TPR), and lime of Tokouto (TL) as control. The AM had the highest initial pH and proton consumption capacity, MS the highest OC content, SC the highest N content, TL the highest CCE and sum of basic cation. Soil pH and basic cations were increased while exchangeable acidity was decreased by addition of all amendments and the effect was greater at the higher rate of application. In terms of lime equivalence, the addition of 20 mg g -1 of AM, MS, PM, CM, GM and SM were equivalent to 2.25,0.02, 0.33, 1.15, 1.05, 0.05 mg g -1 of Ca(OH) 2 in increasing soil pH respectively at least in the short period of this experiment. The high initial pH, base cation and proton consumption capacity also contributed to raise pH of ash, animal or compost amended soil. A first field experiment was carried out to assess the effect of dolomite lime and kraal manure application on growth and yield of maize as well as soil properties in an acid soil (pH= 4.8). The experiment consisted of four rates of lime (L0 =0, L1=325, L3=650 and L4=1300 kg ha -1 ) and four rates of kraal manure (M0= 0, M1=1.25, M2=2.5, M3=5 Mg ha -1 ). The addition of lime at 325 kg ha -1 and manure at 1.25 Mg ha -1 increased soil pH above 5.5 (critical level for Al toxicity), increased soil exchangeable Ca, Mg, K and available P but decreased exchangeable acidity for sole and combined application leading to increased maize growth and yields. The increases in grain yield following the iii addition of lime were 19, 25 and 34 % in 2012 as compared to 23, 22 and 23 % in 2013 by the application of 25, 50 and 100 % of LR respectively. Manure increased grain yield in the order of 19, 12 and 36 % (2012) as compared to 31, 21 and 49 % (2013) respectively with the addition of 1.5, 2.5 and 5 Mgha -1 . The combined use of 100 % LR+5 Mg ha -1 produced the highest yield of 4000-5542 kg ha -1 . Exchangeable acidity was negatively correlated to maize growth and yields highlighting its detrimental effect. The sole application of 25 % of LR (3.14-4.32), 1.25 Mg ha -1 of manure (4.25-6.9) and the combination of 25LR+1.25M (2.36-4.16) were the most economically viable. A second field trial was conducted to evaluate the effect of the combined application of lime and fertilizer on soil acidity and growth and yield of maize. The experiment consisted of two methods of lime application (Broadcasting and Banding), two methods of fertilizer application (Banding and Spot) and four rates of lime (L0 = 0, L1 = 325, L3 = 650 and L4 = 1300 kgha -1 ). Banding of lime had no significant effect on soil pH, exchangeable acidity, and exchangeable K. Application of lime increased soil pH, exchangeable Ca and Mg, and available P, but decreased exchangeable acidity. Spot application of fertilizer had no significant (P>0.05) effect on soil pH, exchangeable Ca, Mg and K and available P. Exchangeable acidity was negatively correlated to maize growth and yields. Spot application of fertilizer increased maize height, biomass and grain yields. The grain yield was increased by 32 % with the spot application of fertilizer as compared to the banding in 2013. Application of 25, 50 and 100% of LR increased grain yield respectively by 22, 25, and 35 % in 2012 and 22, 25 and 40 %, in 2013. Lime banding had the highest net benefit compared to broadcasting and the margins were 57250 and 92500F CFA. The net benefit for spot application of fertilizer was higher than the banding and the margins were 92750 and 220750 F CFA. Application of 25 % of LR had the highest net benefit (675250-757250F CFA). The best combination was broadcasting of lime + spot application of fertilizer+25 % of LR with the cumulative net benefits of 722750 and 962500 F CFA
A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Soil Science