Geospatial Distribution of Some Phosphorus and Potassium Forms as Influenced by Period of Irrigation in the Kano River and the Hadejia Valley Irrigation Schemes, Nigeria.

Abstract

This study was carried out at Kano River Irrigation Project (KRIP) (latitudes 11º 36ʹ 0.05ʺ N to 11º 49ʹ 57.97ʺ N and longitudes 8º 28ʹ 17.02ʺ E to 8º 29ʹ 41.82ʺ E) and Hadejia Valley Irrigation Project (HVIP) (latitudes 12º 17ʹ 48.75ʺ N to 12º 24ʹ 58.28ʺ N and longitudes 9º 51ʹ 31.29ʺ E to 10º 2ʹ17.42ʺ E). The soils are largely deep, well-drained Calcic Luvisols. The aim was to assess the geospatial distribution of some plant-nutrition related forms of P and K. A total of 37 and 19 irrigation sectors were identified in KRIP and HVIP respectively. Google earth was used to tag 109 and 41 sampling points randomly within both developed and undeveloped sectors of KRIP and HVIP respectively. With the aid of projects’ sitemaps, the sectors were demarcated into six periods of irrigation: 0 years (Non -irrigated), 1-10 years, 10-19 years, 20-29 years, 30-39 years and ≥ 40 years as applicable. GPS was used to track the tagged points at the time of sampling. Sur- face soil samples were collected by augering to 30 cm depth with fabricated steel augers. Samples were analyzed for physical and chemical properties. Available (AP) and total (TP) forms of P as well as water-soluble (WSK), exchangeable (Ex. K) and non-exchangeable (NEK) forms of K were analyzed. Basic soil prop- erties were compared by ANOVA using JMP version 12. Geostatistical analysis and Geospatial variability of various forms of P and K were performed with the GS+ software (version 10). Ordinary Kriging was used for the spatial interpola- tion. Texturally, the soils of the KRIP was sandy loam while that of the HIVP was predominantly sandy clayey loam. The pH (mean = 6.68) and EC (mean = 0.21 dsm-1) values across the sites indicated that despite the years of irrigation the areas are not under immediate salinization risk. There was no specific pattern of distribution of basic cations in both the two schemes. There is an observable tendency in the distribution of the forms of P and K evaluated of their being at higher concentrations in longer-periods irrigated lands in both the scheme. The nugget to sill ratio revealed a strong spatial dependence (< 25 %) for WSK. Moderately spatial dependence (25 to 75 %) was observed for available P, total P, noN-exchangeable K and exchangeable potassium. It was concluded that there may be a stronger influence of the irrigation method on the spatial distribution of the forms of the nutrients over other factors such as parent material and weathering.