The prospection of alternative sources of potassium fertilizers has become an imminent necessity in view of the rise in the prices of inputs, aggravated by the global situation of demand and possible crisis in the supply of these products. Enabling the use of national sources not only represents greater autonomy for national agriculture, but also allows for the exploration and use of more sustainable sources in production systems. Thus, the objective of this proposal is to evaluate the efficiency of the application of phonolite as an alternative source of potassium and the addition of bioweathering agents in improving soil quality, in the bioavailability of potassium to plants and in the physiology and productivity of soybean and maize. For this, a field experiment has been studied since March 2019 at Fazenda Experimental Lageado, São Paulo State University, Botucatu, SP. The treatments are constituted by: (I) Control; (II) KCl; (III) Phonolite; (IV) Phonolite + Urochloa ruziziensis; (V) Phonolite + Organic compound and (VI) Phonolite + Urochloa ruziziensis + Organic compound. K sources are applied at a rate of 80 kg ha-1. Soil fertility, the contribution of non-exchangeable K to crop nutrition, soil enzyme activity, crop nutritional status, gas exchange parameters, photosynthetic pigments, Rubisco enzyme activity, protein and carbohydrate concentration in leaves, activity of antioxidant enzymes, components of production and productivity and agronomic efficiency. Normality and homoscedasticity tests will be applied to the data, and when these assumptions are met, they will be subjected to analysis of variance and the LSD test of means (p d 0.05).
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