Soil moisture and nutrient variation within an undulating Manitoba landscape

The use of discrete management units for variable-rate N fertilization requ ires that factors influencing grain yield response to N fertilizer are adeq uately characterized by delineating landscapes into such management units. The objective of this study was to compare the use of topographically deriv ed landform element complexes (LEC) and the use of individual soil series a s management units. Soil volumetric moisture content, nitrate-N, exchangeab le ammonium-N, extractable phosphorus, exchangeable potassium, and sulphate -sulphur were studied in 10 intensively sampled transects in an undulating glacial till landscape near Miniota, Manitoba. The study site was delineate d into upper, mid and lower LEC using a digital elevation model derived fro m relative elevation data. The LEC were useful in capturing gross variabili ty at a manageable landscape scale. Among LEC there was a general trend of lower > mid > upper for median values of soil moisture, nitrate, phosphate, potassium and sulphate, as these attributes generally increased with conve rgent landscape character. Differences among LEC were often statistically s ignificant, and relative distributions exhibited temporal persistence. The site was also stratified by soil series, including Newdale, Varcoe and Angu sville soils (Black Chernozems), which were identified by examination of in dividual soil cores at each sample point. Stratifying the site into managem ent units using soil genetic information, which is reflective of historical moisture conditions and biomass production, was expected to be superior. T here was little advantage, however, in using soil series rather than LEC. S patial distributions of the most agronomically relevant attributes (soil mo isture and nitrate) were expressed at a landscape scale broader than that a t which soil series occurred within the site. While there were important di fferences among soil series with respect to nutrients such as phosphate and sulphate, the site was better stratified by LEC with respect to soil moist ure and nitrate.