Spatial distribution of soil chemical properties for precision nutrient management in soybean production in Kabanyolo Farm, Wakiso District

Abstract

Soybean is one of the most important legume crops in East Africa since it is a great source of both protein and oil. Soybeans have a high demand for plant nutrients in particular nitrogen, phosphorus, and potassium because they determine good root and stem development as well as pod formation. So when deciding how much fertilizer to apply to a soybean crop, it is important to know the nutrient status of the soil in order to avoid under or over application of the fertilizer.It is important to check the specific fertilizer recommendations due to the infield spatial variability across soybean growing regions since soil has a heterogeneous structure and its status affects ecosystem processes which control nutrient cycling. This research therefore aimed at assessing the spatial distribution of major soil chemical parameters (Total N, Extractable P, K, SOM and pH) under soybean fields in Kabanyolo Agricultural farm. Thirty two (32) Geo-coded soil samples were collected from soybean garden of 80m x 40m at a depth of (0-20 cm) based on a grid of 10m x 10m at MUARIK. Sampling locations were obtained by using the Global positioning system (GPS) hand-held device in which latitude and longitude geographical coordinates were recorded for each sampling point. Descriptive statistics were used to describe variation of the data where the co-efficient of variation was used in this study to interpret the variability. The laboratory soil data was analyzed using Ordinary Kriging method. In general, the results showed that the soil had moderate variability with the exception of soil pH. Potassium had a medium variation with CV%= 56.851%.The highest and lowest variations were observed in Phosphorus (CV=84.868%) and pH (CV= 5.735%) respectively. Soil Organic matter and Nitrogen had CV values relatively higher than pH CV with OM (CV=16.086%) and N (CV=16.124%) respectively. Generally, soils in this soybean field are slightly acidic with pH ranging between 4.98 and 6.08. SOM and total Nitrogen had values that were above their critical values in the soil. The soil organic matter in the field ranged from 3.94 to 5.52 while the total Nitrogen in the field ranged from 0.28 to 0.39. Potassium and extractable P had values below their critical values. The Potassium in the field ranged from 0.06 to 0.38. The Phosphorus in the field ranged from 0.84 to 12ppm. According to the results, there is need for site specific management of phosphorus and potassium because of their high variability as well as the pH.