Change in P & K contents of cornstalks over time
The magnitude and distribution of tissue P and K loss increased with increasing precipitation, but this was more consistent for K than for P. Moreover, increasing rainfall from black layer to late fall increased significantly the K loss but not the P loss (not shown). There was large variation in the P and K concentrations and amounts in cornstalks across the sites, but mainly from the black layer stage to late fall. This high variation resulted from differences in soil-test levels, fertilizer rates, hybrids, rainfall and other growth conditions. Contamination with soil and loss of leaves due to wind, which can affect P and K residue concentrations, were not factors influencing the results in this study but may become relevant when working with farm equipment.
The bottom line
Nutrient loss between the black layer and harvest was large for both P and K, loss from cornstalks between harvest and late fall were large only for K, and the overall proportional loss by spring was greater for K. The average P and K concentrations and removal shown in this article, related publications and articles can be used as a general guideline, but due to large variation across fields and years sampling and analysis of harvested cornstalks is recommended to adequately estimate values.
More information from this study, including P and K removal with grain and results of a similar study with soybean, are available in articles written by Mallarino and collaborators in proceedings of the 2011 ISU Integrated Crop Management Conference and the North-Central Extension-Industry Soil Fertility Conference.
The study summarized in this article has been supported in part by the International Plant Nutrition Institute and the Iowa Soybean Association.