Previous research in the Midwest has shown mixed results for varying placement of P and K fertilizers. In a review paper, Boomsma et al. (2007) explained several factors and situations where band applications are likely to be superior to broadcast. These include low P and K soil test levels, soils with high fixation capacity, reduced tillage systems (resulting in cooler soils with smaller root systems), low subsoil P and K levels (partly due to nutrient stratification in reduced tillage systems), cultivar differences, using strip tillage, not using P and K starter fertilizers, and when using automatic guidance for multiple field operations (including controlled wheel traffic). Mallarino et al. (1999) found phosphorus (P) placement method seldom influenced corn or soybean yield regardless of tillage system; however, they also found deep banded potassium (K) increased corn and soybean yields compared to broadcast application mostly in ridge-till and no-till but also in chisel tillage. The yield differences between placements were similar for K rates ranging from 35 to 140 lb K2O/acre.
Minnesota fertilizer guidelines for corn (Kaiser et al., 2022) have substantial rate reductions, up to 50% for very low and low P and K testing soils, when banding compared to broadcasting. No fertilizer rate reductions for band placement are given for soybean as research has generally shown no yield response when banding P (Randall and Hoeft, 1988; Mallarino et al. 1999) and only small yield responses to banded K in soybean (Mallarino et al. 1999). The majority of Minnesota’s deep band placement research was conducted in the late 1980’s and 1990’s in ridge-till. Rehm and Lamb (2004) found deep banded K occasionally increased corn yields in ridge-till but responses were influenced by corn hybrid selection. The primary question is whether deep banding results in greater yields and/or profit as most states do not suggest rate reductions when banding P and K compared to broadcasting regardless of soil test level.
Except for in strip-till, band applications have lost favor for most farmers due to increased farm size, equipment size, equipment cost, and time savings. Broadcast P and K applications are easier, faster and cheaper on a cost per acre of application. Recent record high fertilizer prices have farmers looking for ways to reduce fertilizer costs and increase efficiency and profitability of these inputs while maintaining or increasing yields. Banding P and K at reduced rates may be a viable option for some. Additionally, subsurface banding of P fertilizer can reduce the risk of P runoff compared to broadcast application (Lewandowski et al., 2006), especially in minimal tillage systems.
From 2020 through 2022 a research study was conducted in Waseca and Rochester on clay loam and silt loam soils, respectively. This study compared deep band (6-inch depth) and broadcast placement of P or K for corn at various rates of application and at varied soil test levels in a conservation tillage system. The objectives of this research were to determine 1) whether band applications of P and K are more efficient and profitable than broadcast applications and 2) whether the rate reductions for band applications to corn in the University of Minnesota fertilizer guidelines are warranted. Preliminary results (Vetsch and Kaiser, data interpretation and reporting is on-going at this time) have showed no yield response to P placement. However, band placement of K increased corn yields slightly compared to broadcast in two site-years but reduced yield slightly in one site-year. Additionally, this research showed that reduced rates of P and K fertilizer, even on low P or K testing soils, often produced corn yields equal to or only slightly less than high rates of fertilizer or on higher testing soils. These findings have economic implications for farmers considering reducing P or K rates when fertilizer prices are high, as they currently are.
Often P and K fertilizer is applied for corn and the subsequent soybean crop relies on residual fertilizer. Or enough fertilizer for both crops is applied prior to corn. A recent multi-state project (Boring et al. 2018) found soybean production and yield was not negatively affected by P and K fertilizer application for corn in corn-soybean rotations. However, farmers are concerned that soybean yields may be limited in some conditions. Specifically, when soil tests for P or K are at low levels, when reduced rates of fertilizer P or K are band applied following Univ. of Minnesota fertilizer guidelines for corn and when equipment limitations or salt concerns limit high rates of fertilizer application in deep bands. Due to these concerns, additional research data are needed to determine how placement (deep band vs broadcast) of varying rates of P or K for corn affect subsequent soybean yields. Furthermore, the effects of rate and placement of P or K for corn on subsequent soybean production has not been recently studied in Minnesota.