Mineral Nitrogen and Microbial Biomass dynamics under millet glume compost application in Semi -Arid Niger

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Most farmers in Semi-arid Niger preferably apply composted millet straw to crop fields to enhance fertility status of their soils due to the escalating prices of mineral fertilizers. As a result of the competitive use of the straw, micro-dosing of millet glume compost is emerging as an alternative technology to enhance soil health. However, there is no systematic research on its impact on soil fertility indicators and crop yield. This study therefore aimed to bridge this gap in knowledge by providing relevant data / information on crop and soil response to micro-dose application of the millet glume compost (MGC) within the framework of integrated nutrient management. A field experiment was conducted in 2013 at N‟dounga / Regional Centre for Agricultural Research of Niger (INRAN / CERRA / Kollo). The experiment consisted of the following treatments: 88 g urea + 500 g SSP (MF), 150 g MGC (C 150 g), 150 g MGC + 88 g urea + 500 g SSP (C 150 g + MF) 300 g MGC only (C 300 g), 300 g MGC + 88 g urea + 500 g SSP (C 300 g + MF) and a control (no amendment). The treatments were replicated three times in a randomized complete block design. The results indicated variations in microbial biomass C, N and P as well as NO3- -N and NH4+ -N over the sampling periods of the study. For example, microbial biomass C and N observed at 12 weeks after sowing (WAS) under the amendments were generally higher than values recorded at 4 WAS. Biomass C and N were significantly higher (P > 0.05) under the C 300 g + MF amendment than all other amended plots and the control. Biomass P values were low under all amendments at both periods of sampling (4 and 12 WAS). Biomass C showed significant correlation (P < 0.05) with NO3- (r = 0.74) and organic carbon (r = 0.90) whilst biomass N correlated significantly (P < 0.05) with NO3- -N (r = 0.72) and with total N (r = 0.75). Nitrate-nitrogen levels in the soil increased markedly iv from 8 WAS to 12 WAS indicating the occurrence of Birch effect. Comparatively, the levels of NO3- were generally higher than that of NH4+ at all sampling periods. This has implications for nitrogen loss from the soil system as nitrogen in the form of NO3- is subject to more leaching than NH4+ -N. Sole application of millet glume compost or in combination with mineral fertilizer led to increase in organic C and total N contents of the soil. Millet grain yield obtained under the sole or combined applications of MGC and mineral fertilizers were low due to erractic rainfall patterns. This notwithstanding, C 300 g + MF produced more grain yield than all the amendments. Crop harvest index ranged from 33.42 – 42.7% under the soil amendments. The study indicated that micro-dose rate of 300 g millet glume compost + 88 g urea + 500 g SSP (i.e. 3t/ha compost + 15 N kg/ha + 13 P kg/ha) is potentially ideal for crop growth and soil fertility improvement in Semi-arid Niger.
A Thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science in Soil Science,