Soil Potassium Dynamics In Mollisolls of the Argentine Pampas.

The study of soil potassium (K) might contribute to increase the understanding and comprehension of its soil dynamics; and thus, improve soil management practices and strategies to enhance K availability to crops. The Pampas Region of Argentina is one of the most productive areas of the world, and it is mainly characterized for high soil K content. Following this reasoning, K fertilization practices have been null since the beginning of the agriculture era in this country. The latter promotes a continuous removal of K, which was exacerbated with the introduction of the soybean crops to the Pampas region. The main objective of this study was to evaluate temporal and spatial changes in soil available K under highly productive cropping systems of the Argentine Pampas, without K replenishment. For this purpose, four on-farm experiments were followed during a 10-yr period. Two sites followed a corn (Zea mays L.) – double cropped wheat (Triticum aestivum L.)/soybean [Glycine max (L.) Merr.] rotation and two sites followed the corn–soybean–double cropped wheat/soybean rotation. The treatments evaluated in our research were: i) fields without agricultural history, named as pristine soils (Pr), ii) non-fertilized plots (Check), and iii)  continuous applications of nitrogen (N), phosphorus(P) and sulfur (S) (NPS). The ammonium acetate method was utilized to perform the extractable K (Ke) analysis using soil samples 0 to 20 cm soil depth. Interestingly, two sites presented significant differences in the change of Ke content (final – initial levels), but without showing differences among the evaluated treatments. Additionally, there was a consistent declining Ke trend as the K balance (only K removal by crops) became more negative. The rotation effect was negligible as compared to the influence exerted by the soil type. This behavior was observed in the variation of Ke within a specific soil layer (e.g. 0- to 20 cm soil depth) and/or in the vertical pattern within the soil profile (1 meter soil depth). The soil types (Argiudolls vs. Hapludolls) and the management practices implemented exerted a large influence in the Ke depletion pattern in the non-fertilized and fertilized treatments, “agricultural situations”. A better understanding of K dynamics will provide information that practitioners needed for understanding how K soil fertility changed under different soil types, cropping systems and nutrient management scenarios.