Distribution of Phosphorus and Potassium Following Surface Banding of Fertilizer in Conservation Tillage Systems
Band application of liquid or granular fertilizers is a common practice in maize (Zea mays L.) production systems in some areas of the USA. Our objective in this field study was to determine the relative soil profile distribution of phosphorus (P) and potassium (K) applied as a liquid fertilizer in a surface band. Research was conducted during six years (2001-2006) at three locations in central Iowa. Exchange-resin membranes were used to measure nutrient availability. Phosphorus movement was characterized after 15 kg P ha-1 were dribbled on the soil surface 5 cm to the side of the maize row at the time of planting. The material was a blended combination of 7-9-6 (N-P-K) liquid and 32-0-0 urea ammonium nitrate solution. Potassium movement was characterized after 28 kg K ha-1 were: i) surface broadcast as 0-0-50 (N-P-K) granular fertilizer; ii) applied as a 0-0-50 granular fertilizer in a subsurface band 5 cm to the side of the maize row; or iii) applied as a liquid (0-0-8) surface band 5 cm to the side of the maize row. In 2001, the highest concentration of available P was found at a depth of >7 cm below the surface 43 days after application. In 2002, movement of fertilizer P from the surface (0-2.5 cm) soil layer into the profile (8-10 cm) was evident 43 days after application of both a low N (17 kg N ha-1) and a high N (67 kg N ha-1) material. Given that P diffusion in soil is a relatively slow process, the volume of material applied (280 L ha-1) and the porosity of the soil probably played a role in P movement. Higher concentrations of available K were measured below the soil surface for all three of the K placements 28 days after application in 2004. Similar results were recorded in 2005 and 2006. At the time of the second sampling, K concentrations in treated plots were similar to those in control plots in all three years. Increased levels of available P and K in the root zone could benefit the plant throughout the early part of the growing season. Movement of P and K into the soil will also minimize potential losses by runoff and erosion.