Submitted to: Journal of Sustainable Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/1997
Publication Date: N/A
Interpretive Summary: There is considerable concern regarding the effects of cropping on the quality and productivity of the soil. Although the effects of cropping on soil organic matter, nitrogen, and other indicators of soil quality have been studied for many years, most of the studies have been conducted under controlled conditions where crops and cultural and fertilization practices are well defined. We studied the effects of cropping by farmers, using their own cultural and fertilization practices on soil quality as measured by soil organic matter, total nitrogen, extractable phosphorus and pH. Soil samples from 27 locations in Oklahoma were obtained and analyzed in conjunction with wheat fertilization studies during 1951-57. Final samples were taken and analyzed in 1992. The results of the study indicate that although there are some cases in which soil quality is being reduced, many farmers are growing continuous wheat without degrading soil quality. These eresults indicate that most wheat farmers in Oklahoma are using practices that are not especially degrading to soil quality, thus we need not be concerned that our soil resources are being unduly exploited.
Technical Abstract: Most studies in which soil properties are monitored are conducted under controlled conditions where crops and cultural and fertilization practices are well defined. We measured soil organic carbon (OC), total N, NaHCO3- extractable P, and pH in farmers fields at 27 Oklahoma sites in the 1950s and again in 1992. Most of the sites were in areas commonly cropped to continuous wheat (Triticum aestivum L.). We also sampled soil at 2 sites with native sod to determine changes in soil properties since initial cultivation. One of the 27 sites was planted to tall fescue (Festuca arundinacea Schreb), in the late 1970s. On the 26 sites still in cultivation in 1992, surface (0 - 15 cm) OC had decreased at 11, increased at 13, and was unchanged at 2 sites. Total N had decreased at 7 sites, increased at 6 sites, and remained unchanged at 13 sites. NaHCO3- extractable P had decreased at 2 sites, increased at 15 sites, and remained dunchanged at 9 sites. Soil pH had decreased at 15 sites, increased at 8 sites, and remained unchanged at 3 sites. These results indicate that although there are some cases in which soil quality is being reduced, many farmers are growing continuous wheat without degrading soil quality. Virgin Grant silt loam lost 45% of its surface (0 - 15 cm) OC in 25 yr and 59% in 92 yr of cultivation. Respective losses in total N were 23 and 46%. Kirkland silt loam surface soil had lost 42 and 47% of its initial OC after 58 and 92 yr in cultivation. Respective losses of total N were 29 and 36%. At the site converted to grassland, OC and total N increased sharply, extractable P was unchanged, and pH was increased, probably as a result of lime application. Results obtained on this site may be indicative of changes occurring on land in the Conservation Reserve Program (CRP).