Soil Fertility Dynamic on a Long Term Cropping Systems in the Northern Great Plains.

A long-term cropping system study was started in 1987 at the NDSU Carrington REC to determine the effects of crop rotation, tillage, and fertilizers on soil fertility, crops yield, biomass production and diseases. The study consists of three 4-year crop rotations (1- hard red spring wheat [HRSW], sunflower, barley, soybean; 2- HRSW, field pea, corn, soybean; and 3- HRSW, corn, soybean, canola), three tillage systems (conventional, minimum and no-till), and four fertility treatments (nitrogen [N] rates and sources). Urea is applied on rates of 0, 50, and 100 lbs of N/ac to non-leguminous crops each spring, and composted manure is applied at 200 lbs of N/ac (every 4 years in the spring). The goal of this study was to determine the effects of crop rotation, tillage system, N rates and sources on soil fertility during the last two crop rotation cycles (2007-2014). Soil samples were taken at the end of each growing season at depths of 0-6, 6-12 and 12-24 inches and submitted for routine soil analysis, plus nitrogen. Soil fertility maps were created using the soil analysis results. Nitrogen source and rates were the main factors affecting soil fertility. Plots that received composted manure showed higher P levels and tend to have higher soil pH, while plots receiving urea (100 lb N/ac) showed a trend of lower soil pH values. Even applied once every 4 years, composted feedlot manure increased soil P content. Beef feedlot composted manure should be used as P source, instead of N source, in areas where soil P content is high and where there is a potential for runoff and water P contamination. The decreasing soil pH values on the plots treated with urea can be an indicative of N leaching. Continued studies are necessary to confirm these findings.