Abundância da microbiota, diversidade metabólica e teores de C e N em latossolo sob sistemas de produção de soja e algodão

Abstract

Understanding the effects of plant diversity on microbial soil community will improve the comprehension of the production systems impacts on carbon (C) and nitrogen (N) cycling. Thus, we evaluated the abundance of microorganisms, microbial metabolic diversity, the contents of C and total nitrogen, and the N forms (microbial biomass-N, ammonium-N and nitrate-N) on soybeans and cotton production systems. The evaluations were conducted in two periods and the systems were composed by monocultures, successions and crop rotations. For soybeans, it was studied the monoculture (soybean/fallow (S/F)), the succession (soybean/millet (S/m) and soybean/corn (S/C)), rotations ([soybean/millet - soybean/ crotalaria - corn + brachiaria (R1)] and [soybean/crotalaria - soybean/corn + brachiaria - brachiaria (R2)]). For cotton, the successions studied were (millet/cotton m/C and brachiaria/cotton b/C), and the rotations were ([sunn hemp/cotton - millet/Cotton - soybean/corn + Brachiaria (R1)], [millet/cotton - soybean/corn (R2)] and [millet/ cotton - crotalaria/soybean - corn + brachiaria (R3)]). The systems were in the sixth year of implementation. The first evaluation was conducted when the soybean was at the beginning bloom and the second one was conducted when the soybean was at the full maturity stage and cotton at the beginning bloom. It was not detected differences between the abundance of Bacteria and Fungi on soil samples collected in both experiments, regardless of the cultures and their previous appearances in successions and rotations of different systems. In the case of Archeaea, the effect observed was the largest abundance in the S/F system, even so, just at the first evaluation. When these three groups were jointly analyzed by a multivariate technique, the S/F system has got less abundance than all other soybean systems and the B/C system was the smallest of other cotton production systems. The number of the N cycle micro-organisms, the metabolic diversity of the microbial community and the contents of C and N total do not differ between soy production systems. In the cotton production systems, the number of nitrifying was smaller than in systems m/C, B/C, and R1, only at the first period and m/C showed fewer denitrifying by the second period, in R3 metabolic diversity was lower the C content did not differ between systems and N content was lower in the system b/C in the first time. We conclude that, after six years, the use of systems with more species richness in succession or rotation on the clayey soils in tropical regions does not produce changes in the abundance of Bacteria, Fungus and Archeae, the number of N cycle micro-organisms, the metabolic diversity of the microbial community and the C and N content.