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Title: Potassium management during the rotation from alfalfa to corn

item YOST, MATT - University Of Minnesota
item Russelle, Michael
item COULTER, JEFFREY - University Of Minnesota
item SHEAFFER, CRAIG - University Of Minnesota
item KAISER, DANIEL - University Of Minnesota

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2011
Publication Date: 9/26/2011
Citation: Yost, M.A., Russelle, M.P., Coulter, J.A., Sheaffer, C.C., Kaiser, D.E. 2011. Potassium management during the rotation from alfalfa to corn. Agronomy Journal. 103(6):1785-1793.

Interpretive Summary: Plants require adequate nutrient supplies for high yields. However, it is not always easy to predict how much extra is needed to supplement nutrient supply from the soil. Adding too much can reduce plant growth or quality, reduce profit, and contaminate soil, air, or water. Potassium is an important nutrient for crops like alfalfa, but the cost of this fertilizer increased about three-fold in recent years, making it more important to provide good recommendations to farmers. Field research was carried out on 10 Minnesota farms to learn what rate of fertilizer was needed during the last year of alfalfa production and to discover whether excess potassium remained available for the next corn crop. The soil in these fields tested 'medium' in potassium supply, which means that yield response could be expected. We found that alfalfa did not produce more or better quality forage with potassium than without. Furthermore, although excess potassium improved corn yield the following year, it was better to apply the fertilizer to corn rather than alfalfa. These results may help farmers avoid unnecessary costs while maintaining crop yield and quality.

Technical Abstract: High potassium (K) fertilizer prices in recent years have made it imperative for growers to apply optimum K rates to alfalfa (Medicago sativa L.). Current University of Minnesota fertilizer guidelines in the Corn Belt do not change for the last production year when alfalfa stand persistence is not a major concern. Furthermore, little is known about carryover of K applied to alfalfa on first-year corn (Zea mays L.) grain and silage yields. From 2008 to 2010, on-farm research was conducted on 10 fields with medium soil test K (STK) to determine response to K for alfalfa yield and quality in the last production year and to estimate K carryover to first-year corn. Alfalfa yield and relative feed value (RFV) and quality (RFQ) did not improve with K fertilization. Herbage K concentration and K uptake increased with K fertilization across sites, indicating that applied K was available during the season of application. When K was not applied to the corn, each 100 kg/ha increase in the index of available K increased corn grain yield by 0.5 Mg/ha, decreased stover yield by 0.4 Mg/ha, and did not affect silage yields. Regardless of K rate applied to alfalfa, additional K applied to corn increased corn stover and silage yields by 10 and 8%, respectively. This suggests that carryover K was less available than K applied to corn. On medium STK soils going into the last year of alfalfa, applying fertilizer K to first-year corn rather than alfalfa may enhance economic return.