The Impact of Row Spacing On Sediment and Phosphorus Losses in No-till Soybeans.

The Soil Erosion Service (now called the Natural Resources Conservation Service) first demonstrated soil conservation practices for farmers in the 1930’s, which has had lasting impacts on farming and soil management. No-till planting, a soil conservation practice that focuses on the management of crop residue, has increased dramatically in usage over the last few decades. It has been shown to decrease sediment transport drastically compared to conventional tillage practices (Dabney, 1993). The amount of farms that use no-till practices in the United States nearly doubled between 1994 and 2004 (Peterson, 2004). Row spacing is another aspect of soil conservation that has been shown to control sediment transport (Troeh, 2004). However, more information is needed to understand how residue management strategies in conjunction with different row spacing effects sediment transport.  

The proposed research will quantify sediment transport and phosphorus losses in soybeans planted at two row spacings (30” and 7.5”) into two residue types (corn and soybean). Each treatment will be planted into a 40 ft2 plot, and replicated twice for a total of eight plots. All of the treatments will be planted into fields containing Valton Series (Fine-silty Mollic Paleudalf) soil on 15% slopes in La Crosse County, Wisconsin, a region that experiences significant soil erosion due to steep slopes.The soybeans will be planted around the first week of May. The seed used will be of maturity group I and will be treated with fungicide and inoculants. No fertilizer will be added to the field at planting time. Applications of herbicides will be carried out as needed throughout the growing season to avoid the disturbance of weeds in the treatments.

Each plot will be isolated from the surrounding field using a sheet metal barrier as constructed by Dolliver et al. (2009). At the downslope end of each plot a 52 gallon basin will be installed to facilitate the collection of surface runoff waters. The collection basins will be covered to ensure that only runoff is able to enter.  The metal barriers and basins have already been constructed and tested during preliminary field trials. After each rainfall event, 500 mL samples of runoff water will be taken from each collection basin. The remainder of the runoff will be removed from the basins. Each runoff sample will be labeled according to treatment and date, and in addition, rainfall totals will be recorded for each event. All runoff samples will be analyzed for sediment and phosphorus concentrations at the end of the growing season. Two 40 mL of suspended runoff will be extracted from each sample bottle and placed in a 40 mL tins, where the samples will be dried at 105 oC. The dried sediment left in the tins will be weighed and total sediment concentration determined. Soluble phosphorus will be analyzed by filtering water samples through a 0.45 µm filter and analyzed using the absorbic acid method on a HACH DR/2400 spectrophotometer (EPA method 365.2).

The data will be statistically analyzed to determine the effects of row spacing and residue type in no-till soybeans. Significant differences will be evaluated at a probability level of P<0.05. This presentation will discuss the results from the 2010 growing season.