On-farm evaluation of variable rate sulfur application

Kirk Stueve/Yuxin Miao

The objectives of this project are to 1) determine within-field variability of optimum S rates in commercial corn fields; 2) identify soil and landscape factors influencing corn responses to S fertilizer applications; and 3) evaluate the potential of variable rate S fertilizer applications for corn in Minnesota.

The number of farmers applying sulfur (S) fertilizers to corn fields is increasing. However, studies of S applications reported mixed results. S fertilizers are mainly applied at uniform rates across a field, unavoidably resulting in under- or over-applications. No studies have been reported on the within-field variability in corn responses to S fertilizer application and optimum S rates and the potential of variable rate S application. The overall goal of this project is to conduct on-farm trials in commercial corn fields to evaluate the possibility and potential benefits of variable rate S application in Minnesota. On-farm S rate trials will be conducted in 3 fields selected in different parts of Minnesota.

Five different S rates (0, 12.5, 25, 37.5 and 50lb S/ac) will be used, and each field will be delineated in grids of 70-80 ft wide and 150-200 ft long. One grid will have one S rate, and five grids next to each other covering the five S rates form a block. The treatments will be randomly ranged in each block and the block will be replicated across each field. Intensive soil sampling will be used to determine soil available S, organic matter, soil texture and other related soil properties. Digital elevation models will be created using Lidar data and terrain attributes will be calculated. Geospatial analysis will be performed to determine within-field variability in optimal S rate. Machine learning models will be used to identify key variables influencing corn yield and corn responses to S application. The potential benefits of variable rate S application will be determined in comparison with uniform S application and no S application treatments. A variable rate S recommendation strategy will be explored based on the key influencing factors identified in this study. The results of this project will provide important guidelines for precision S management of corn in Minnesota.