Gypsum and potassium application to acid soils for maize (Zea mays L.) production in La Frailesca, Chiapas, Mexico

Introduction. Maize (Zea mays L.) production in La Frailesca region, Mexico, is limited by sandy soils, low in potassium (K), and with acidic arable layers and subsoils. There is information on the management of lime but not on amendments that could be used for subsoil acidity — such as gypsum — nor on the interactions between amendments for soil acidity and K fertilization. Objective. To evaluate the effects of K and gypsum on maize and on previously limed soils. Materials and methods. The evaluations were conducted in farmers’ fields in La Frailesca region, Chiapas (Mexico) in 2016 and 2017. Four gypsum rates (0, 1.25, 2.5 and 5 t ha-1) and four K rates (0, 60, 90, and 120 kg ha-1 as K2O) were factorially combined in a randomized block design, with three replicates. In both years, before the beginning of the experiments, dolomitic lime was applied to the experimental area following standard practices. Responses of crop yield, soil exchangeable K, Ca, Mg, and Al, and soil pH were obtained. Results. Maize yields increased with gypsum (stabilizing at 1.25-3.0 t ha-1), and K (stabilizing at 70-120 kg ha-1 of K2O) applications. In soils, K application increased exchangeable K content, while gypsum increased exchangeable Ca content and pH, and decreased exchangeable Al content. Liming increased pHCa and exchangeable Ca and Mg contents, and lowered the exchangeable Al content in the top 7.5 cm of soil. Conclusion. Soils with exchangeable K (≤0.3 cmolc kg-1) were responsive to K fertilization. The positive effects on yields from gypsum were probably linked to a greater Ca supply in the top 7.5 cm. These results are encouraging about the benefits of the combined application of dolomitic lime, gypsum, and K, but longer evaluations are needed to properly determine the effects of gypsum on subsoil acidity.

Use of a New Deep Vertical Gypsum Placement Practice on Corn and Soybean Production in Conservation Tillage Systems

Corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) production in claypan soils in the north central U.S. may be constrained by the presence of acidic subsoils. Subsoil acidity can inhibit root growth leading to decreased drought tolerance and grain yields. In conservation tillage systems, management options to incorporate gypsum applications may be limited; thereby reducing available practices to lower subsoil acidity. The objective of this study was to determine the effects of surface placement of gypsum compared to a new practice for deep vertical placement of gypsum on corn and soybean plant growth and yields in a conservation tillage system. Field trials were conducted from 2012 to 2016 in northeast Missouri (USA) with treatments of gypsum (0, 2.9, and 5.2 Mg ha-1) broadcast on the soil surface or applied in a deep vertical band to a depth of 51 cm. Surface and deep banding of gypsum had inconsistent effects on corn and soybean plant heights, plant population and yields. However, deep banding of gypsum resulted in a 6.4 to 9.8% decrease in corn yields and a 9.9 to 13.0% decrease in soybean yields depending on the time after application. These results indicate that further research is warranted in conservation tillage systems in claypan soils to examine modification to the deep vertical placement practice or combining applications of surface-applied gypsum and deep placement of lime in order to develop a practice that will be more effective in overcoming subsoil acidity.