Browsing by Author "Opoku, Andrews"

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    Fertilizer micro-dosing increases crop yield in the Sahelian low-input cropping system: A success with a shadow
    (Soil Science and Plant Nutrition, 2016) Ibrahim, Ali; Abaidoo, RC; Fatondji, Dougbedji; Opoku, Andrews
    Over the years, a scarcity of information on nutrient gains or losses has led to overemphasis being placed on crop yields and economic income as the direct benefits from fertilizer micro-dosing technology. There is increasing concern about the sustainability of this technology in smallholder Sahelian cropping systems. This study was designed in the 2013 and 2014 cropping seasons to establish nutrient balances under fertilizer micro-dosing technology and their implications on soil nutrient stocks. Two fertilizer micro-dosing treatments [2 g hill−1 of diammonium phosphate (DAP) and 6 g hill−1 of compound fertilizer Nitrogen-Phosphorus-Potassium (NPK) (15-15-15)] and three rates of manure (100 g hill−1, 200 g hill−1 and 300 g hill−1) and the relevant control treatments were arranged in a factorial experiment organized in a randomized complete block design with three replications. On average, millet (Pennisetum glaucum (L.) R.Br.) grain yield increased by 39 and 72% for the plots that received the fertilizer micro-dosing of 6 g NPK hill−1 and 2 g DAP hill−1, respectively, in comparison with the unfertilized control plots. The average partial nutrients balances for the two cropping seasons were −37 kg N ha−1yr−1, −1 kg P ha−1yr−1 and −34 kg K ha−1yr−1 in plots that received the application of 2 g DAP hill−1, and −31 kg N ha−1yr−1, −1 kg P ha−1yr−1 and −27 kg K ha−1yr−1 for 6 g NPK hill−1. The transfer of straw yields accounted for 66% N, 55% P and 89% K for removal. The average full nutrient balances for the two cropping seasons in fertilizer microdosing treatments were −47.8 kg N ha−1 yr−1, −6.8 kg P ha−1 yr−1 and −21.3 kg K ha−1 yr−1 which represent 7.8, 24.1 and 9.4% of N, P and K stocks, respectively. The nutrient stock to balance ratio (NSB) for N decreased from 13 to 11 and from 15 to 12 for the plots that received the application of 2 g DAP hill−1 and 6 g NPK hill−1, respectively. The average NSB for P did not exceed 5 for the same plots. It was concluded that fertilizer micro-dosing increases the risk of soil nutrient depletion in the Sahelian low-input cropping system. These results have important implications for developing an agro-ecological approach to addressing sustainable food production in the Sahelian smallholder cropping system.
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    Sustainability of Crop Residues and Manure Management in Smallholder Cereal-Legume-Livestock Systems in the Savannas of West Africa
    (September, 2011 ) Opoku, Andrews
    The integration of crops and livestock is an effective means of harnessing and recycling nutrients in manure and crop residues to improve crop yields. However, the competing demands for crop residues within the farm present a tradeoff between increasing crop yields and sustaining livestock productivity. The effectiveness of manure as fertiliser on the other hand is constrained by poor handling and storage techniques. This thesis addresses the challenges associated with crop residues and manure management in five studies: i) assessment of nutrient balances, ii) quantification of tradeoffs, iii) appraisal of the sustainability of crop residue uses, iv) evaluation of manure management options and v) quantification of added benefits from integrated use of mineral fertiliser and manure. The NUTMON framework was used to assess the N and P balances in cereal-legume-livestock farms at Cheyohi, Ghana (Ferric Luvisols), Sarauniya, Nigeria (Regosols) and Garin Labo, Niger (Eutric Gleysols). Nitrogen balances ranged from -7 to -22 kg ha-1 with the application of the recommended N rate and -34 to -82 kg ha-1 in the absence of fertiliser use. The application of the recommended rate of P led to the P accumulation in the order of 3 to 7 kg ha-1. However, without the application of fertiliser, P depleted at rate of 2 to 7 kg ha-1 annually. The tradeoffs for allocating crop residues between the crop and livestock units of the farm were evaluated by incorporating 0, 25, 50, 75, and 100 % of haulm and stover yield of the farm into the soil and feeding the remaining amount to small ruminants. The tradeoffs estimates favoured the incorporation of 75 % haulm and 25 % stover at Cheyohi, 25 % haulm and 75 % stover at Sarauniya, and 0 % haulm and 0 % stover at Garin Labo. An agricultural sustainability index was used to appraise the sustainability of the five management scenarios. The use of 75 % of haulm and 25 % of stover as soil amendment was found to be the most sustainable option in Farm 1 at Cheyohi. Other sustainable options were, the total removal of crop residues in Farm 1 at Sarauniya and Garin Labo, and the use of 75 % of haulm and 25% of stover as soil amendment in Farm 2 at Sarauniya. The effects of oil cakes and manure storage methods on nutrient losses during composting were evaluated at Nyankpala, Zaria and Maradi. The storage of manure in heaps or pits and fortification with oil cake had no effect on N and P losses during composting at all locations. The use of plastic sheets to cover heaps or line pits significantly reduced N losses from 29 – 67 % to 5 – 30 % and P losses from 25 – 37 % to 2 – 20 % at Nyankpala and Zaria but had no effect on nutrient losses at Maradi. The added benefits and economic returns from the combined application of mineral fertiliser and manure were evaluated at Nyankpala, Sarauniya and Maradi. Added benefits in grain yield ranged from -68 to 470 kg ha-1 at Nyankpala and -514 to 684 kg ha-1 at Sarauniya. No added benefits were found at Maradi. The most cost effective application rates were 2.5 t ha-1 of manure complemented with either 25 % of the fertiliser recommendation at Nyankpala or 50 % of the fertiliser recommendation at Sarauniya.