Carvão hidrotérmico em solo cultivado com feijão-caupi sob irrigação com e sem solução salina: efeitos na estabilidade e resistência tênsil de agregados

Abstract

The cowpea (Vigna unguiculata (L.) Walp.) holds economic, nutritional, social, and cultural significance for farmers in the northeastern region of Brazil. Addressing soil salinity in arid and semi-arid areas is imperative, as elevated salt levels in the soil constrain the cultivation of most crops. The incorporation of amendments, such as hydrochar, has emerged as a viable strategy to alleviate the adverse effects of salinization on the physical and chemical attributes of the soil. In this context, hypotheses were formulated, positing that hydrochar derived from cashew bagasse, owing to its carbonaceous nature, contributes to augmenting aggregate stability in water, diminishing tensile strength, and similarly mitigating the deleterious impact of salt accumulation on the structural stability of soil cultivated with cowpea and irrigated with saline water. The overarching objective, therefore, was to assess the impact of hydrochar from cashew bagasse on water stability and the tensile strength of aggregates. This encompassed na evaluation of its potential as a mitigator of sodium's detrimental effects on the structural stability of soil cultivated with cowpea and irrigated with saline water. Additionally, the study aimed to ascertain the optimal dose of hydrochar that maximizes the structural stability of soil cultivated and irrigated with saline water. The investigation took place in a greenhouse affiliated with the Department of Soil Science at the Federal University of CearÝ (UFC), located on the Pici campus. PVC columns containing soil with a preserved structure and cultivated with cowpea were employed. The experimental design followed a completely randomized factorial scheme of 5 x 2 x 2 (comprising five hydrochar doses: 0, 5, 10, 20, and 40 Mg ha-1; two irrigation waters: saline and non-saline; and two soil layers for analysis in the column: 0-0.1 and 0.2-0.3 m). The study incorporated four replications, resulting in a total of 80 observation units. Subsequently, aggregates were collected from each column for a detailed analysis of stability and tensile strength. The obtained data underwent analysis of variance (ANOVA), with mean comparisons executed using Tukey's test at a 5% significance level. It is concluded that the application of hydrochar produced from cashew bagasse contributes to increasing the stability of aggregates in water, with a dose of 40 Mg ha-1 being the most effective, and that biochar is efficient in reducing the opposing effects of salt accumulation on the stability of soil aggregates cultivated with cowpea and irrigated with saline water. Although no effect of biochar doses on the tensile strength of aggregates, was found the beneficial effects of its application mitigating the harmful effects of salinity in the surface layer of the soil.