THE IMPACT OF NUTRIENT MANAGEMENT OPTIONS ON SOIL ORGANIC CARBON POOLS AND MAIZE YIELD IN NORTHERN GHANA

ABSTRACT

Exponential growth in human population has led to the exploitation of natural resources e.g. organic matter reserves for crop production. Various interventions such as manuring, fertilization, green manuring etc. have been proposed to enhance continuous crop production. However, the sustainability of these methods are unknown. Soil productivity depends largely on organic carbon stocks (SOC). The labile organic matter fraction or pool is associated with nutrient dynamics and responds sensitively to changes in management namely tillage, manuring, fertilization, mulching, etc. The objective of the study was two-fold: first to investigate the impact of three management practices, namely: manure application, fertilizer application and farmer practice (no fertilization application) on SOC fractions and the total SOC (TOC) and second, how these practices affect maize production at three sites: Nyankpala, Dimabi and Savelugu, in the Northern Region of Ghana.

The procedure involving permanganate oxidizable carbon (POXC) was used to determine labile and non-labile pools of SOC of soils for each management practice. Changes in percentage carbon is used to determine Carbon Pool Index (CPI) which expresses the changes in the labile pools of soils under management relative to that of a virgin soil and Lability Index which is a measure of good soil conditions (LI). These two indices were used to estimate a Carbon Management Index (CMI) which is used in studies to monitor both soil degradation and agricultural yields.

Results indicate that nutrient levels increased in the order; manure >> fertilizer >> non-fertilizer Also, the carbon pool index (CPI) values which indicate the extent of degradation and rehabilitation were in the order Nyankpala >>> Dimabi >> Savelugu (fertilized) > Savelugu (non- fertilized). In addition, CMI were 50.6, 47.6, 39.9 and 24.9 for Nyankpala, Dimabi, and Savelugu, respectively. The results show that management affected mainly the labile carbon pool. The relationship between labile carbon (CL) and TOC for Nyankpala was: CL=0.003 x TOC2-0.0023 x TOC+0.0219; R2=0.81 that for Dimabi was CL=0.0199 x TOC-0.058: R2 = 0.93 and that for Savelugu were, CL=0.02 x TOC-0.088: R2 =0. 90 and CL=0.0005 x TOC2-0.0008 x TOC+0.0212 R2=0.91 for Fertilized and non-fertilized, respectively. The application of manure at Dimabi, manure Nyankpala, fertilized farm and non-fertilized farm yielded 2701.56 kg/ha, 2267.37 kg/ha, 2944.81 kg/ha and1060.24 kg/ha respectively. The findings suggest that manure management practice had significant impact on maize yield and this in turn was via the CL but not the TOC. With exception of fertilized field at all sites, the maize yield correlated well with the CL. Thus given a management practice and the manner it impacts on CL, maize yields could be predicted if other climate variables do not constraint the production.