Assessment of soil fertility status and potential for okra production at Rajaf Demonstration Farm, South Sudan

Abstract

Soil fertility assessment is an essential step towards improving agricultural production. In tropical and sub-tropical regions of the world, Okra (Abelmoschus esculenta L. Moench) is a food security and income sourcing crop. This study investigated the impact of continuous cropping on Rajaf Demonstration Farm’s (RDF) soil fertility status and the potential for Okra production. Soil samples for laboratory analysis and a pot experiment were randomly collected from the field in RDF. Thirty six composite soil samples were collected for physicochemical analysis (Soil texture, pH OM, TN, P, CEC and micronutrients), 144 undisturbed soil cores for bulk density and total porosity collected at 0-15, 15-30 and 30-60 cm depth from the cultivated, fallow and virgin sections of the farm and 1,600 kg of soil was collected from the cultivated section at 0- 30 cm depth for the pot experiment. For the pot experiment, Okra seeds were treated to 4 rates of N and P, and 3 rates of K; N (0, 25, 50 and 75 kg N ha-1), P (0, 20, 40 and 60) kg P ha-1 and K (0, 30 & 60) kg K ha-1 giving 48 fertilizer combinations, which were replicated thrice to give a total of 144 experimental pots which were laid out in a Completely Randomized Design in a greenhouse. Data was collected during flowering, on number of leaves per plant, plant height; stem diameter, pod yield and plant dry matter. Results showed that there is a wide variability in soil chemical properties, with the virgin land showing better soil properties compared to the cultivated and fallow lands. For pot experiment, fertilizer combinations of NPK significantly increased growth and yield (398.77g) of Okra as compared to control 44.04g, with the highest yield obtained with the combination of 50:40:60 kg ha-1NPK, respectively. Continuous cropping over the past 35 years on RDF affected the soil's chemical properties to the extent that most of the properties are below the critical limits for soil productivity and that, in order to improve Okra yield, a combination of NPK inorganic fertilizer at a rate of 50: 40: 60 kg ha-1 respectively, is required.