Maize response to potassium and amendments for soil acidity in La Frailesca, Chiapas, México

One of the major soil degradative disorders affecting the La Frailesca region in Chiapas is soil acidity. Although this problem has long been recognized, its management has consisted only in applying around 2 t/ha of dolomitic limestone. Soil analyses done in 2013 showed that subsoils (15 to 30 cm deep) can be equally or more acidic than plow layers, and such condition is unlikely to be ameliorated by the recommended lime application. Moreover, low exchangeable K is widespread in the dominant sandy soils of La Frailesca, and K limitations might be exacerbated by the higher pH and added Ca and Mg brought about by liming.

Previous observations have shown that maize performance was more markedly affected when exchangeable Al exceeded 20% of the effective cation exchange capacity. In 2014, we used this value to select two locations with acidity problems in the topsoil only, and four locations with exchangeable Al above the threshold both in topsoil and subsoil.

To amend acidity in the topsoil only, dolomitic limestone was applied at a rate sufficient to reduce exchangeable Al below 20%, whereas where subsoil acidity was high, gypsum was applied at 5 t/ha. These amendment rates were combined with three K₂O rates (0, 90 and 180 kg/ha) when only lime was applied, and two K₂O rates (0 and 120 kg/ha) when gypsum was also applied.

Increased maize yields were obtained with the application of amendments or K in all locations; however, the greatest yield response was observed when the amendments and the highest K rate were applied together.