Submitted to: North Central Extension Industry Soil Fertility Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/20/1997
Publication Date: N/A
Interpretive Summary: A basis for variable-rate fertilizer applications in cropping systems is that there exists variability in soil nutrient supply to crop plants. This understanding is currently only extended in practice to various locations within a field as measured with grid soil sampling. Variability in nutrient quality may also be significant when considering the variation in nutrient pool depth across the landscape. The research question addressed in this study is--can a more accurate prediction of P and K nutrients be made by considering topsoil thickness. Topsoil thickness could especially be helpful in fertility recommendations for soils highly variable in this parameter, such as the claypan soils in Missouri. The relationship between topsoil depth and nutrient availability as measured using standard soil testing methods was very weak for the 60 sites that were sampled. This means that topsoil depth probably is not a good indicator of nutrient availability. However, crop response to fertility was found to be enhance by good soil water content levels, and this was highly correlated to topsoil depth. The impact of this research is that it may result in improved methods for measuring soil nutrients. Producers will be able to target their fertilizer applications to specific areas of the field where they are most needed, which will increase profits. Producers and the public will benefit because fertilizer over-applications which cause impairment to water quality will be reduced.
Technical Abstract: Variability in nutrient quality may be significant when considering the variation in root zone depth across a landscape. Research was initiated to (1) determine and/or evaluate the relationship between topsoil depth and phosphorus (P) and potassium (K) nutrient availability for the Mexico-Putman association of claypan soils, and (2) determine the responsiveness of crops to added P and K fertilizer as affected by topsoil thickness and surface nutrient availability. While topsoil thickness and sampling depth parameters were significant in explaining P and K variability, model fitness values were relatively low. The models show an increase in available P with an increase in topsoil thickness for all sampling depths. Regression models showed a decrease in available K with an increase in depth of sampling and topsoil thickness. While topsoil thickness was significant in explaining the P and K availability, total variability among fields was not explained by topsoil thickness. Crop response to various soil-test P and K levels and varying topsoil thickness showed that yield was enhanced more by good soil water content levels, and this highly correlated to topsoil depth, than by soil-test P and K.