Dairy Manure Application Frequency and Crop Rotations Influence Off-Farm Fertilizer Needs and Soil Fertility Balance.

Dairy farms often grow forages for their dairy herd and import grain, enabling them to increase animal units per hectare over time, often resulting in manure nutrient accumulation and a high soil test P. In Pennsylvania, all livestock farms are required to have manure management plans, but farms with 2 AUE/A (2.24 Mg of animal liveweight/ha) have excess manure and require certified manure management plans. We hypothesized that even with a lower animal stocking rate, if dairy manure is applied frequently and to crops with low P and K removal, over time off-farm fertilizer need would decline and soil fertility levels increase to above optimum. On cropland that did not have a manure application history, we applied dairy manure to three, no-till crop rotations that differed in crop nutrient removal and manure application frequency (3, 4 or 6 applications over eight years). Two diverse rotations produced forages (corn silage and alfalfa and orchardgrass) and together produced all the feed and forage for a 0.561 Mg of AUE/ha dairy farm, one rotation was a corn grain and soybean rotation. We measured soil fertility before we initiated the experiment, and in years 3 and 6. Soil tests and estimated crop nutrient needs informed a nutrient management plan that included starter fertilizer. Within a few years, the nutrient management plan and soil tests indicated that supplemental P fertilizer was not needed in all rotations, P levels were often in excess of crop needs, and supplemental K fertilizer needs declined. Less supplemental K was needed in the corn grain-soybean rotation than in the rotations with forages, but also in rotations with more frequent manure applications. As hypothesized, a dairy farm with a low stocking rate, can have fields accumulate high nutrient levels associated with frequent manure application even with significant crop nutrient removal.