Change in Phosphorus and Potassium Contents of Cornstalks Over Time

Increasing corn yield and harvest of cornstalks for feed, bedding or bioenergy production are generating numerous questions about phosphorus (P) and potassium (K) concentrations in cornstalks and removal. The functions of P and K in plants influence their accumulation in different plant parts, and also may influence the magnitude of losses from live tissue or residue. A larger proportion of the total plant P is in grain compared with K, and most of the absorbed P is incorporated into the plant organic matter but K is in the inorganic soluble ion form. Therefore, P and K amounts removed by cornstalk harvest, concentrations and recycling to the soil may vary and over time be affected by rainfall and other factors. Also, high temporal soil-test variation, mainly for K, points to a potentially important effect of P and K recycling

Phosphorus and Potassium Placement for No-Till Corn

The information presented is part of ongoing research to identify effective fertilizer placement methods and diagnostic tools for phosphorus (P) and potassium (K) in no-till and ridge-till corn and soybean. Results for no-till cornfields will be emphasized here. There is uncertainty about soil test interpretations and cost-effective methods of fertilizer application for the no-till system. Moreover, producers are uncertain about the value of soil testing in conservation tillage because of large variability and lack of knowledge concerning techniques for collection of samples. Broadcast placements are less costly than banded placements but they seem inefficient for no-till fields because fertilizers are not incorporated. Because of the reduced movement of P and K in soils, broadcast applications result in stratification of these nutrients and accumulations within the top 2 or 3 inches of the soils. Although residue cover usually improves root growth and root absorption efficiency at shallow soil layers, the stratification could result in lower P or K uptake by plants during dry periods

Corn and Soybean Potassium Uptake, Removal with Grain, and Recycling to the Soil

Many field trials have been established and evaluated at the ISU Northern Research Farm, Kanawha, Iowa to study potassium (K) fertilization rates and placement methods on corn and soybean grain yield, K uptake, and soil-test K values. However, no research has investigated K recycling to the soil by maturing plants and crop residue until the next crop is planted. The amount and the timing of the K recycled to the soil should have a significant impact on soil-test K values, and should explain a great deal of usually very high soil-test K temporal variability. Therefore, plots of several ongoing field K trials were used to investigate these issues

Potassium Fertilizer Effects on Yield of Corn and Soybean and on Potassium Uptake and Recycling to the Soil

Research has been conducted in Iowa to investigate potassium (K) fertilization of corn and soybean, but not at this farm. Insufficient K amounts in the soil or applied with fertilizer or manure significantly decreases crop yield end economic benefits to growers. Also, research in other locations has shown large soil-test K temporal variability within a season or from the fall to spring. Therefore, a study was initiated in 2009 to investigate these issue

Long-term Evaluation of Hybrid, Nitrogen, and Potassium Interactions in Continuous Corn

A long-term experiment was established in 2009 to study continuous corn responses to potassium (K), nitrogen (N), and hybrid rootworm resistance. Previous research suggested a need for this study. A long-term trial conducted until 2001 at the ISU Northern Research Farm showed that the maximum corn yield level and the N rate that maximized yield was higher when K was optimal or greater. In contrast, the relative yield response to N and the N rate that maximized yield were similar for soil-test phosphorus (P) levels ranging from very low to very high. Other studies have shown that rootworm resistance often increases yield compared with untreated susceptible hybrids. Also, that rootworm resistance does not consistently affect the K rate that maximizes yield, but increases K removal because of the higher yield levels. Therefore, this new study evaluates possible interactions between rootworm resistance and N and K fertilization in corn

Potassium Effects on Yield of Corn and Soybean and on Potassium Uptake and Recycling to the Soil

Considerable research has been conducted in central Iowa to study potassium (K) fertilization rates and placement methods on corn and soybean grain yield, K uptake, and soil-test K values. However, no research has investigated K recycling to the soil by maturing plants and crop residue until the next crop is planted. The amount and the timing of the K recycled to the soil should have a significant impact on soil-test K values, and should explain a great deal of usually very high soil-test K temporal variability. Therefore, plots of several field K trials in central Iowa were used to investigate these issues

Corn and Soybean Response to the Micronutrients Boron, Manganese, and Zinc Applied to the Soil

Prior research on micronutrients fertilization for corn and soybean has been scarce in Iowa and has shown inconsistent yield responses. Therefore, the objective of a study conducted during 2012 and 2013 was to assess effects of boron (B), manganese (Mn), zinc (Zn), and their mixture on corn and soybean grain yield. Iowa State University has no interpretations of soil or tissue tests for micronutrients, other than for Zn in corn and sorghum

Potassium Uptake and Recycling to the Soil in Corn and Soybean

Considerable research has been conducted at this farm to study potassium (K) fertilization rates and placement methods on corn and soybean grain yield, K uptake, and soil-test K values. However, no research has investigated K recycling to the soil by maturing plants and crop residue until the next crop is planted. The amount and the timing of the K recycled to the soil should have a significant impact on soil-test K values, and could explain a great deal of usually very high soil-test K temporal variability. Therefore, plots of several field K trials at this farm were used to investigate these issues

Corn and Soybean Potassium Uptake, Removal with Harvest, and Recycling to the Soil

Research has been conducted at the ISU Northeast Research Farm for many years to study potassium (K) fertilization rates and placement methods on corn and soybean grain yield, K uptake, and soil-test K values. However, no research has investigated K recycling to the soil from maturing plants and crop residue until the next crop is planted. Because all plant K is soluble in water, the amount and the timing of the K recycled to the soil should have a significant early impact on soil-test K values, and should explain a great deal of usually very high soil-test K temporal variability. Therefore, plots of several field K trials at this farm were used to investigate these issues

Nutrient uptake by corn and soybean, removal, and recycling with crop residue

The prevailing phosphorus (P) and potassium (K) management system in Iowa and the Midwest is based on soil testing, response-based fertilizer application for low-testing soils, and removal-based fertilizer application to maintain desirable soil-test P (STP) and soil-test K (STK) values. Several issues are important for an effective implementation of this management concept. These include use of appropriate soil-test methods and field calibrations to determine optimum soil-test levels and fertilization rates, knowledge of fertilization and cropping impacts on soil-test values over time, and reliable estimates of P and K removal with harvest. In Iowa, continued research during the last two decades has provided calibrations for various soil-test methods for P and K, which have been used for existing soil-test interpretations in Iowa State University (ISU) Extension publication PM 1688. This publication also suggests to use estimates of P and K removal to maintain optimum STP and STK values, assuming there is a good relationship between P and K removal and STP or STK trends over time. Research during the last two decades has shown large temporal variability of yield and both STK and STP but very large for STK. Therefore, better study of the relationship between P or K removal and STP or STK in the short term and long term should be useful to improve the effectiveness of P and K management for crop production and to maintain acceptable water quality in Iowa