A County-Level Assessment of Manure Nutrient Availability Relative to Crop Nutrient Capacity in Iowa: Analysis of Spatial and Temporal Trends

During the twentieth century, agricultural production strived to achieve increased food production in order to satisfy both local and export demands. In many cases, this led to increased farm sizes and an operational separation of crop and livestock production. Society fears that the trend of increasing centralization and industrialization of agriculture, specifically animal agriculture, has resulted in concentration of waste products associated with their production (manures, wash-down water, process waters, etc.) over relatively small geographic regions that are spatially segregated from crop production areas. Since the distance that manure can be economically hauled for land application has practical limits, this could lead to over-application, of manures near animal feeding facilities, potentially increasing nutrient losses to ground and surface waters. A statewide analysis of crop and animal production in Iowa suggests that about 25% of current nitrogen and phosphorus requirements for crop production could be supplied from manures and litters, while around 40% of the required potassium could be provided. However, neither livestock nor crop production is uniformly distributed across all counties. This unequal distribution suggests that a more disaggregated analysis of crop nutrient requirements and manure nutrient supply is necessary to estimate the risks of excess nutrient loss to the environment. Results indicated that in general all counties had sufficient nutrient utilization capacities to value manure as a resource; however, counties in Northwest Iowa are becoming progressively more manure rich, while counties in Southwestern and Central Iowa are becoming progressively more manure poor. This separation of crop and livestock production is becoming more pronounced, indicating that solids separation and nutrient (especially phosphorus) recovery systems that can concentrate manure nutrients for transport could become more important to help counties maintain nutrient balance and to return manure nutrients to the soil if these trends persist

Kinetics of Phosphorus Sorption in Vegetative Treatment Area Soils

Vegetative treatment systems have been proposed and are being utilized to treat runoff from animal feeding operations. These systems use soil and vegetation to remove contaminants (solids, phosphorus, and nitrogen) from the feedlot runoff water and limit potential impacts runoff could have on water quality. Research has shown that these systems soils play a key role in retaining the phosphorus. Thus, the purpose of this experiment was to determine the rate of phosphorus sorption by the soil and in so doing evaluate the impact the runoff contact time with the soil has on phosphorus removal from the solution and retention in the soil. In this experiment, a phosphorous solution of 100 mg P/L, taken to approximate concentrations in the feedlot runoff, was added to soil samples obtained from three different locations in Iowa. After adding the phosphorous solution to each soil sample, the sample was continuously mixed and a sample of solution collected at 0, 1, 2, 4, 7, 14, 21 and 28 days to measure the amount of phosphorus remaining in solution. The results indicated that in most cases phosphorus was quickly sorbed as equilibrium was reached within approximately 24-hours. This indicates that relatively short contact times are required to phosphorus removal; however, in several cases phosphorus removal occurred more slowly and might place a limit on appropriate application rates. The results indicated that phosphorus sorption generally occurred more quickly in VTA soils than in the grass soil samples. Based on the measured sorption parameters, VTA areas ranging from 0.5 – 2.25 hectares are required per hectare of feedlot area

Lab Investigation of Nitrogen Application Timing, Nitrogen Source, and NZoneMax Addition on Nitrate Leaching

Proper manure and nutrient management is essential to ensure maximum crop production while reducing the risk of N losses. There is concern, that fall application of liquid swine manure can lead to economic and environmental concerns due to potential for losses of nitrate. Thus, the objective of this study was to evaluate the impact of application timing (fall vs. spring) and use of NZoneMax applied with liquid swine manure (LSM) or urea had on nitrogen loss. The study was conducted as a laboratory soil incubation over 35-days with leaching performed on days 3, 7, 10, 14, 21, 28, and 35. Treatments included a control soil receiving no nitrogen application and treatments of LSM or urea fertilizer applied at a rate of 168 kg N/ha (150 lb N/acre) applied with and without NZoneMax, tested on two different Iowa soils, and simulating a spring and fall application. In the spring application soil incubations began immediately after fertilizer application occurred, for the fall applications fertilizer sources were added soils were placed in a freezer for 3 months and then brought to room temperature where they were incubated for 35 days. Results indicated that application timing, nitrogen source, additive, and the application timing x nitrogen source factors were all significant with less nitrogen leaching occurring from the spring application, the manure as compared to the urea, and fertilizers receiving the NZoneMax treatment. In general, NZoneMax reduced nitrate leaching by 13% over the incubation while spring versus fall application reduced leaching by about 35%. Manure initially leached nitrogen more slowly than urea; however, by day 28 of the incubation the difference was no longer statistically significant. These results provide insight into how different fertilization choices may impact nitrogen loss