Soil Fertility Evaluation for Cashew Production at Iyapo Farm Estate, Offa, Kwara State

Cashew (Anacardium occidentale L) is an important commodity crop with great potential as a foreign exchange earner. It is grown principally for it nuts and apple and is a hardy crop which is adapted to a wide range of agro-ecologies. The increase in the price of cashew nuts globally, has resulted in increased interest in the cultivation of cashew. The Management of Iyapo farms limited in its desire to key into this sector requested the technical assistance of Cocoa Research Institute of Nigeria (CRIN) to carry out soil fertility evaluation of the 50 hectares of land proposed for establishment of cashew. The farm was divided into three main sections (A, B and C) based on topography and four land use types (water logged, cassava plot, previously cultivated land and excavated land). Section A was parallel to River Oyun followed by section B in the middle of the farm, while the last section C ran parallel to the road from Ijagbo town. The land use types were scattered within the three blocks. The water logged area was however confined only to section A which was close to river Oyun.

Soil samples were collected at soil depths of 0-20 cm and 20-40 cm soil depth and at a distance of 20 m apart. The soil collected was put in nylon bags and properly labelled. Soil samples collected were air dried, passed through 2 mm sieve and analyzed for some of its physical and chemical properties. In section A, total soil nitrogen at 0-40 cm soil depth ranged between 0.07 g kg-1 to 0.18 g kg-1 with a mean value of 0.11 gkg-1 soil while mean soil available phosphorus at 0-40 cm soil depth was 3.16 mg kg-1 The exchangeable potassium content across 0-40 cm soil depth ranged between 0.09cmol kg-1 to 0.35 cmol kg-1 with a mean value of 0.25 cmolkg-1 and 0.19 cmol kg-1 for 0-20 cm and 20-40 cm soil depth respectively. In section B, nitrogen across the various soil depths ranged between 0.04 gkg-1 to 0.12 gkg-1 with nitrogen content of the soil decreasing with increasing soil depth. This falls below the soil critical level of 1 gkg-1 required for cashew and was grossly inadequate to meet nitrogen need for cashew. There is need for nutrient supplementation as nitrogen fertilizer is required to meet the nitrogen needs of the cashew. Similarly, phosphorus was also inadequate across the soil depths with a range of 2.47 mgkg-1 to 4.51 mgkg-1 across the various soil depth and a mean value of 3.24 mgkg-1 and 2.65 mgkg-1 for 0-20 cm and 20-40 cm soil depths respectively. This was below the soil critical value of 3.7 mgkg-1. There is therefore need to apply phosphorus fertilizer to boost cashew productivity.

Soil exchangeable potassium was adequate across the various soil depths with a range of 0.13 to 0.20 cmol kg-1 and a mean value of 0.18 cmol kg-1 and 0.16 cmol kg-1 for 0-20cm and 20-40 cm soil depths respectively. There is no need for potassium fertilizer application. The results above indicated that sections A, B and C requires 180 kg ha-1 of urea and 31.5 kg of Single Super Phosphate (SSP). The cassava plot and previously cropped bare land requires 189 kg ha-1 urea and 9.9 kg ha-1 SSP, while the excavated land requires 194.2 kg urea 25.8 kg SSP and 32.28 kg MOP. Cashew should not be grown on the water-logged section.