Nutrient Uptake, Mineralization, and Movement in Irrigated Calcareous Soils Receiving Dairy Manure Applications
Idaho is the 4th leading dairy cattle producing state in the United States with a standing herd of 550,000 as of May 2008. Nitrogen and phosphorus in dairy manure can be transported to waterways, posing serious health and environmental threats. The direct impact of dairy manure on phosphorus concentrations in streams has not been evaluated in Idaho. The Idaho DEQ has also documented an increase in nitrogen concentrations in groundwater wells located in Idaho watersheds containing large dairies. However, these same watersheds also receive substantial nitrogen inputs fertilizers, septic systems, and other non-point sources). The primary source(s) of nitrate pollution in these watersheds have not been identified. Potato growers are also concerned that they will not be able to predict when nitrogen in the manure will be converted from the plant
unavailable organic form to plant available inoganic forms that can be used by the crop. The objectives of this research project are 1) to determine the effect of manure application timing prior to planting on plant available nitrogen concentrations in the soil during the cropping season, 2) to evaluate the effect of dairy manure applications to potatoes on plant available nitrogen and phosphorus concentrations, petiole nitrate concentrations, tuber yield, and tuber quality, and 3) to quantify the impact of dairy manure applications on nitrate and dissolved phosphorus concentrations in runoff and leachate in first order streams. To meet the first objective, soils combined with dairy manures as well as soils from fields that received dairy manure applications several years prior will be kept at temperatures simulating both fall and spring temperatures, and frequently analyzed for plant
available nitrogen concentations. From this research, we will be able to provide growers with estimates on nitrogen availability of dairy manure applied to soils at varying times prior to planting. This will lead to greater nitrogen use efficiency, which will improve yield production while reducing nitrate leaching. To meet the second objective, potatoes will be planted on soils that have received both recent and non-recent applications of dairy manure. Soils and potato plant tissue will be tested for nitrogen and phosphorus concentrations. Potato tuber quality and quantity will also be determined. With the results from this study, potato growers will have the opportunity to reduce fertilizer costs and nitrate leaching losses by applying manures at times and rates that are most comparable to the potato growth patterns. To meet the third objective, water draining from crop fields that
have and have not received manure applications will be tested for nitrogen and phosphorus concentrations. Understanding how dairy manure applications impact nitrogen and phosphorus concentrations in first-order streams will provide state government agencies an effective starting ground for determining how to reduce hazardous concentrations of phosphorus and/or nitrogen levels in streams.