Nutrient placement and tillage: A few things to consider
Assistant Professor Soil Fertility & Plant Nutrition
Department of Crop Sciences
Phosphorus (P) and potassium (K) are two very important plant nutrients. The application of these nutrients represents a large investment to producers. With the rising cost of fertilizer and fuel and greater awareness of the impact of agriculture on the environment it is important to understand how management of these nutrients and the soil can increase both profit and environmental benefits. Conservation tillage practices along with broadcast P and K applications can lead to accumulation of these nutrients in the soil surface, but is this really a problem? Should we be doing more intensive tillage or deep-banding these nutrients to make them more available to crops and to reduce the potential for these nutrients, especially P, to runoff in surface water? Is it possible to maintain the same yield level with less fertilizer when nutrients are band-applied compared to broadcast applications? Is there an environmental benefit to conservation tillage that is also cost effective? These are all important questions with complex answers. Ongoing studies conducted over the last few years may help us find some answers.
When most of the P and K fertility is present in the surface layer of the soil, these nutrients can become less available to crops during dry periods. For this reason, many prefer to apply nutrients at soil depths that might not be as affected by drying conditions as the soil surface. Strip-tillage, a conservation tillage practice that is considered by many as a twist to no-till systems, lend itself to subsurface band applications because it is relatively easy to apply nutrients during the tillage operation. After three years of band applications of fertilizers in tilled strips located at approximately the same location within the field we are seeing decline in surface P and K levels and increase concentrations at the subsurface where the fertilizer is being applied. Our study has not shown a yield advantage to deep-placement of P and K compared to broadcast applications, but there might be environmental benefits by reducing P levels at the surface layer. Also, there is no evidence suggesting that fertilization rates can be reduced with band applications compared to broadcast applications. Finally, even though we did not see yield benefits by deep placement of fertilizers, we saw yield benefits due to strip-tillage for both corn and soybean (Figures 1 and 2). Likely, by moving crop residue off the planting row, strip-tillage seems to improve seedbed and early-season soil conditions and allows the crop to get off to a better start (Figures 3 and 4).
Figure 1. Three-year mean corn yield for different tillage and P and K application methods. No-till broadcast (NT-BC), no-till deep-placed at 6 inches with a low disturbance knife (NT-DP), and strip-till deep-placed at 6 inches (ST-DP). Values followed by same letters are not significantly different (P>0.05).
Figure 2. Three-year mean soybean yield for different tillage and P and K application methods. No-till broadcast (NT-BC), no-till deep-placed at 6 inches with a low disturbance knife (NT-DP), and strip-till deep-placed at 6 inches (ST-DP). Values followed by same letters are not significantly different (P>0.05).