TOWARDS OPTIMIZATION OF ALTERNATE-SOURCE POTASSIUM APPLICATIONS IN CONSERVATION TILLAGE SYSTEMS FOR MAIZE PRODUCTION
Adoption of conservation tillage systems is known to result in increased soil K stratification. Yet, there have been few investigations into the optimization of K management in these tillage systems, particularly regarding the placement and timing of K-based fertilizer applications. Additionally, there are many unknowns regarding the influence of tillage timing with/ without K fertilizer application. Increased availability of fertilizers containing both macro- and micro-nutrients, such as Aspire™ (which includes both K and B), has coincided with new questions about potential micronutrient deficiencies in maize (Zea mays L.) production. Previous research has investigated the influence of K and B individually; however, few university studies utilize multi-nutrient fertilizer sources. These knowledge gaps prompted a series of field investigations into the impacts of alternative tillage/ placement of Aspire™ on maize growth and development. Because K stratification is thought to potentially limit K availability to maize, tillage/fertilizer placement treatments involving no till (NT), fall strip-till (FST), spring strip-till (SST), and fall chisel (FC) were compared with at least two application rates of Aspire™ (ranging from 0 to 108 kg K ha-1) from 2016 to 2019 on Indiana soils with moderate exchangeable K concentrations. Maize was grown in rotation with unfertilized soybean (Glycine max L) planted after strip-till.
Although tillage systems, other than no-till, were intended to decrease stratification, little change in vertical stratification for in-row samples was observed in the strip-till systems when Aspire™ was band applied at the time of strip-till (indicating fertilizer application was limited to the top several centimeters of soil). Few interactions were evident in maize response between tillage/placement and Aspire™ applications; however, superior V6-stage growth/nutrition responses to Aspire™ application occurred in fall tillage systems (FST or FC). The latter was especially true when comparing the two strip-till timings (FST and SST) at three rates. In addition to early season plant nutritional benefits, plant stature also benefited from Aspire™ across tillage/ placement systems (e.g., ~20% increase in height at V8, plus a leaf area index (LAI) gain at V14 of ~10%) reflecting on the potential to increase the source capacity of fertilized maize plants. By R1, there was little synergism between treatments in the tested parameters, indicating little difference among the tillage/ placement methods (and strip-till timing), and few immediate consequences from 50% rate reduction for Aspire™ in the strip-till systems. Although grain yield increases of 4-8% were common when Aspire™ was applied, yield component analysis showed little interaction between tillage/placement and Aspire™. Grain yields were shown to be more highly correlated and had significant relationships to earleaf K at R1, and less so with minor changes in B concentrations at R1.
Aspire™ application at the full and 50% rate commonly benefited plant nutrition and grain yield, but little synergism between Aspire™ application and tillage/ placement system was evident. Although rate reduction did not show immediate consequences to plant nutrition in either strip-till timing, longer-term research is necessary to better understand future consequences from this management practice. The lack of differences in response to strip-till timing (fall vs. spring) shows the potential for flexible timing when optimum tillage conditions are present. This research confirmed the importance of K fertilization to maize performance, but the efficient management of K requires further inquiry.