Contribuição da microbiota do solo no crescimento do algodoeiro em sistemas consolidados e recém-implantados de sucessão soja/algodão

Abstract

Farmers report reduced cotton growth and productivity when initially replacing corn in the soy/corn succession, even under adequate chemical and physical soil conditions. The biology of the soil in consolidated soybean/cotton areas may be influencing the availability and absorption of nutrients. The objective of the study was to investigate the effect of successive cultivation of the soybean/cotton system on the availability and absorption of nutrients, microbiological conditions of the soil and initial growth of the cotton plant. Two experiments were carried out in a greenhouse, namely: (1) cultivation time and (2) dilution/autoclaving, the soil from both were collected in Sapezal-MT. The experiment (1) was carried out in a completely randomized design (CRD), with 5 treatments with soil from different histories/time of soybean/cotton cultivation (T0 - consolidated soybean/corn cultivation; T1 - first year soybean/cotton; T2 - second year soybean/cotton; T3 - third year soybean/cotton and T4 – fourth year soybean/cotton), with three repetitions. Experiment (2) was carried out in CRD with a factorial scheme (4 × 2), with soil from consolidated soybean/cotton cultivation (≥10 years). Four proportions of soil (25, 50, 75 and 100%) in relation to autoclaved sand and two microbiological conditions (AS – autoclaved soil and NAS – non-autoclaved), with three replications. The experimental unit consisted of a vessel, being: (1) one liter and (2) two liters. After 30 days (1) and 40 days (2) the following were evaluated: dry mass of the shoot (SDM), roots (RDM) and total (TDM); concentration and accumulation of foliar nutrients; nutrient content and P fractionation in the soil; microbial biomass and soil biochemistry, root colonization by arbuscular mycorrhizal fungi (AMF) and critical P level for cotton (CL). The data were subjected to analysis of variance, Tukey test and Pearson correlation.There was no effect (p ≥ 0.05) on plant growth in experiment (1), however, there was an increase in the concentration and accumulation of P and AMF due to the increase in soybean/cotton cultivation time. Experiment (2) also increased leaf P and AMF due to microbiological preservation, in addition, a 36 and 58% increase in SDM and RDM production in 100% NAS soils, respectively, when compared to 100% AS. As for AMF, treatment T4 in (1) obtained an increase of 49%, 53%, 82% and 10% in relation to T0, T1, T2 and T3, respectively and (2) presented an average of 84% and 2% for AS and NAS, respectively. In the 100% AS treatment of (2), the P content was three times lower than the 100% NAS, remaining below the CL for cotton, and in (1) only T4 is within the CL. The 100% NAS treatment increased 41% in labile P (Mehlich-3 extractor) compared to 100% AS and the T4 treatment increased 79, 64, 81 and 32% compared to T0, T1, T2, T3 and T4, respectively. It is concluded that plant growth in consolidated soybean/cotton systems is due, in part, to the action of microorganisms on P lability and better absorption by arbuscular mycorrhizal fungi.