Does Blanket Fertilizer Recommendation Still Work? A Case Study of Maize Production in Northern Ghana.

Farmers in northern Ghana continue to use blanket fertilizer recommendations based on soil tests and experiments that are several decades old. Consequently, maize yields obtained by smallholder farmers are small fractions (< 40%) of potential yields, despite increases in the use of NPK fertilizers. To achieve sustainable growth in productivity, it is critical to consider the spatial soil fertility variability in order to re-design soil fertility recommendations. We collected over 15000 georeferenced soil samples across the entire northern region of Ghana to identify the limiting nutrients, and to develop soil fertility maps to aid site- and crop-specific fertilizer recommendations. The Grid/Management Zone Hybrid Soil Sampling Method was used to collect the soil samples. Within each community, fields were subdivided into an arrangement of cells of 2-4 km apart. Within each cell, management zones are established using a variety of resources and/or datasets. To validate soil analytical results, plant tissues samples were collected for analysis. The combined results of the soil and plant tissue analyses show that across the entire region, the soils are generally acid to slightly acidic with very few isolated cases where the soil pH is near neutral. Large portions are deficient in P (< 10 mg kg-1), S (< 6 mg kg-1), zinc (< 1 mg kg-1), B (< 1 mg kg-1) and K (< 80 mg kg-1). Therefore, to increase productivity, farmers need to supply these limiting essential plant nutrients to crops, and not limit themselves to the blanket application of only NPK fertilizers. To make site-specific fertilizer recommendations, nutrient omission trials are needed to identify quantities of each limiting nutrient to apply for sustainable increases in productivity and farm incomes.
Agyin-Birikorang, S., S.A. Nuhu, A.-R.A. Fuseni, H.W. Dauda, J. Fugice Jr., W. Bible, C. Sylvester, A. Mobley, and U. Singh. 2019. “Does Blanket Fertilizer Recommendation Still Work? A Case Study of Maize Production in Northern Ghana,” presented at International Annual Meeting of Soil Science Society of America at San Diego, California, January 6-9, 2019.