Method of Soil Sampling following Subsurface Banding of Solid Manures

Soil sampling guidelines do not exist for fields fertilized with solid manures applied in bands. The objective of this work was to describe the distribution of mineral nutrients and total C and propose a method of taking soil samples that represent the fertility level of a field following manure application in narrow bands below the soil surface. Systematic soil core samples were taken from no-till cotton (Gossypium hirsutum L.) plots fertilized with poultry litter in subsurface bands spaced approximate to 1 m apart and analyzed for total C, total N, and extractable P, K, Mg, Cu, Mn, Fe, and Zn. The results showed that total C and most of the mineral nutrients were not evenly or randomly distributed in the space between and across the bands because of the manure placement in narrow bands, nutrient movement away from the band, and plant uptake. Concentrations of P, K, Mg, Zn, Cu, and B in the soil samples taken over the band were elevated by up to 50 fold compared to the positions away from the band. This distribution shows that taking random soil samples from fields fertilized with manures in bands is not appropriate and that some systematic sampling schemes must be used to more accurately represent the soil nutrient status. We describe a new sampling method that takes into account the band width and the spacing between consecutive bands. The method is based on a proportional mixing of soil cores taken at predetermined distances from the manure band including one core directly over the band.