Data on the vegetative response of cowpea to fertilizer application on three selected benchmark soils of the Upper West region of Ghana

Declining soil fertility among smallholder farmers in the Savannah zones of Ghana, among other issues, is triggered by continuous cultivation, low fertilizer use and low soil organic matter content. The area is faced with insufficient domestic production, food insecurity and poverty, all of which constitute major constraints to national development. Continuous cultivation leads to low soil organic matter levels. To build up the soil organic matter levels, residue incorporation is a major factor to be considered. Cowpea is grown in these areas for the grain yield while the residue is incorporated into the soil to gain maximum benefits of the nitrogen fixation. We present the physical and chemical properties of three benchmark soils in the Savannah zones of Ghana as well as their vegetative response to NPK fertilizer application. The FAO soil classification also helps in the thorough understanding of the soil and an appropriate management option for optimal productivity is recommended.


a b s t r a c t
Declining soil fertility among smallholder farmers in the Savannah zones of Ghana, among other issues, is triggered by continuous cultivation, low fertilizer use and low soil organic matter content. The area is faced with insufficient domestic production, food insecurity and poverty, all of which constitute major constraints to national development. Continuous cultivation leads to low soil organic matter levels. To build up the soil organic matter levels, residue incorporation is a major factor to be considered. Cowpea is grown in these areas for the grain yield while the residue is incorporated into the soil to gain maximum benefits of the nitrogen fixation. We present the physical and chemical properties of three benchmark soils in the Savannah zones of Ghana as well as their vegetative response to NPK fertilizer application. The FAO soil classification also helps in the thorough understanding of the soil and an appropriate management option for optimal productivity is recommended.

Value of the data
• This dataset will be valuable for researchers, extension workers and farmers in choosing appropriate soil management practices for optimal and sustainable crop production in the Upper West region of Ghana. • The data will allow researchers and farmers to determine the suitability of the soil to support the production of cowpea and other legumes in general. The information may also be used by the Government to formulate an appropriate policy and intervention strategies for increased food production for the growing population. • The data provide insight on the effect of fertilizer treatments and soil types on the vegetative growth of cowpea. Cowpea requires balanced nutrition of nitrogen, phosphorus and potassium for vegetative growth. The vegetative part of the crop forms the biomass that is returned to the soil which helps in the buildup of soil organic carbon. • This data will be a guide to farmers in the investigated areas on the best fertilizer combination for optimum performance of cowpea. It will also be a guide for long term investigation into soil nutrient dynamics for sustainable cowpea production in the investigated regions.

Data description
The data are from 40 experimental plots in each of the 3 sites located in each of the investigated soil types. This was collected from three benchmark soils of the Upper West region of Ghana, West Africa. This region is of utmost importance as it is part of the "breadbasket" region of Ghana. The soil profile differentiations and characteristics observed in the field for the three soils (Dondori, Kojokpere and Nyoli) are presented in Tables 1 -3 , respectively. It shows the horizon descriptions, depth, drainage and FAO classification of each soil. The physical and chemical properties of the soil profile pit at different depths for each location are presented in Table 4

Experimental design, materials, and methods
Soil profile pits were dug for the soil classification. The different layers were identified and soil samples collected from each layer for laboratory analysis. The soil color was determined using the Munsell color chart. The soil samples from the different layers were analyzed in the laboratory using standard laboratory protocols. Soil pH was determined using a glass electrode pH meter in a 1:1 soil to distilled water (soil: water) ratio, available P by the Bray and Kurtz (Bray P-1) method [3] while the modified Walkley and Black procedure as described by Nelson and Sommers [4] was used to determine organic carbon. Total nitrogen was determined using     the macro Kjeldahl method [5] and 1.0 N ammonium acetate (NH 4 OAc) extract was used for exchangeable bases. Exchangeable acidity (hydrogen and aluminium) was determined in 1.0 N potassium chloride (KCl) extract [6] . Exchangeable bases were extracted using 1.0 N ammonium acetate. Potassium and sodium in the soil extract were determined by flame photometry using standard solutions. Effective cation exchange capacity was calculated by the sum of exchangeable bases (Ca, Mg, K, and Na) and exchangeable acidity (Al and H). Percent base saturation was calculated from the sum of exchangeable bases as a percent of the ECEC of the soil.
The fertilizer was spot applied at sowing using urea, triple superphosphate and muriate of potash. Glyphosate and hand weeding were deployed for weed control. Data were taken at 2-  week intervals from the second week after sowing (WAS) until the sixth WAS and was stopped after flowering.

Conflict of Interest
The authors declare no competing interest.