The period of implantation of the no-tillage system (NTS) is a fundamental factor to the dimension of the changes that occur to the soil's physical, chemical and biological attributes. Thus, the objective of this study was to evaluate the soil changes to the physical attributes and correlate the results to the soil organic matter in areas of different long-term soil management. The study was set as a completely randomised design, in a 4 × 4 factorial scheme, with four management systems [5 years NTS (NTS5); 17 years NTS (NTS17); conventional tillage system for 20 years (CTS20); native area (NA)], and four soil depths (0-0.05, 0.05-0.1, 0.1-0.2, 0.2-0.4 m), with five repetitions. Soil mechanical resistance to root penetration (RP), bulk density (SD), volumetric moisture (VM), macro (Ma), microporosity (Mi) and total porosity (TP), and the aggregation parameters were evaluated. The CTS20, NTS5 and NTS17 presented superior SD in the most superficial soil layers, which was not yet causing resistance to root development. The SD was the only physical attribute that correlated significantly with all the other soil attributes evaluated, indicating the importance of such attribute to evaluate soil quality to crops. The soil physical attributes found in the Cerrado native area followed the sequence of similarities: no-tillage system with 17 years (most similar), with five years and the conventional tillage system (less similar). The changes caused by the anthropic activity in the soil's physical attributes are more pronounced and perceptible in soil depths up to 0.2 m.
The objectives of this study were to evaluate the stability of aggregates, and quantify the contents and stocks of total organic carbon (TOC), and granulometric and humic fractions of soil organic matter (SOM). Four management systems were evaluated: (1) a no-tillage system (NTS) implemented 5 years ago (NTS5); (2) NTS implemented 17 years ago (NTS17); (3) conventional tillage system (CTS) implemented 20 years ago (CTS20); and (4) native Cerrado vegetation. For each system, five undeformed and five deformed soil samples were collected from the 0.00–0.05, 0.05–0.10, 0.10–0.20, and 0.20–0.40 m layers. The weighted mean diameter (WMD), TOC, stock of carbon (StockC), organic carbon particulate (OCp), organic carbon associated with minerals (OCam), stock of OCp, stock of OCam, carbon stock index, carbon management index (CMI), organic carbon in the fulvic acid fraction (FAF), humic acid fraction (HAF), and humin fraction were quantified. The WMD and CMI values increased as the soil management intensity decreased. The adoption of the NTS increased the WMD and the contents, stocks, and proportions of TOC in the more labile granulometric and humic (FAF/HAF) fractions of the SOM. The WMD, CMI, granulometric and chemical fractionation of the SOM were more efficient than the TOC and StockC in identifying the differences between the management systems. Due to the higher contents of the more labile fractions of SOM, the granulometric and chemical fractionation of SOM in the NTS5 and NTS17 systems had higher values of WMD and CMI than the CTS20 system.
The decomposition of plant residues, the changes in the total organic carbon (TOC) and the fractions of soil organic matter (SOM) occur differently in irrigated areas. The objective of this study was to quantify the biomass production, the decomposition of cover crops residues and relate them with the changes n the content and fractions of SOM in an irrigated area of vegetable crops. Six types of cover crop treatments were evaluated: brachiaria (B); sunn hemp (S); millet (M); B + S; B + M; S + M, plus an additional treatment (native area), with 4 repetitions. The production of fresh (FB) and dry biomass (DB), the rate of plant residue decomposition, TOC, SOM fractions and the coefficient of SOM (QSOM) were quantified. It was observed that the greatest and the lowest volume of crop residues were from the B and S cover crop, respectively. The cover crops in monoculture presented great decomposition rates and short half-life when compared to mixtures of cover crop. The TOC and QSOM were great in the 0 to 0.05 m soil layer, and in the M + S cover crop mixture, when compared to the 0.05 to 0.1 m soil layer and to other cover crops. Among the SOM fractions, the humin predominated in the most superficial soil layer (0 to 0.05 m).
AGRADECIMENTOSInicialmente agradeço a Deus, que em Cristo Jesus anunciou nossa esperança e, com base em seu sacrifício, busco me aprimorar a cada dia para cumprir seu chamado e dar um novo passo em direção ao que Ele tem reservado para mim. Sem Ele, não haveria uma lista de pessoas e instituições incríveis e essenciais para que este trabalho tomasse forma. Agradeço aos meus maiores espelhos terrenos, meu pai Denilson e minha mãe Ana Paula, que sempre carregam um percentual de todas as minhas conquistas por merecimento. E que o agradecimento se estenda ao meu irmão, Danrlley, meu amigo inseparável e minha namorada Lídia, minha eterna e principal companheira. Guardo um agradecimento especial ao meu orientador Prof. Dr. José Luiz Rodrigues Torres, com quem compartilhei muitos ensinamentos e compreendi a relevância daquilo que hoje eu profissionalmente faço com tanto prazer.Agradeço aos muitos amigos que tiveram sua parte nessa conquista, em especial ao Venâncio Rodrigues e Silva, pois juntos dividimos intensas dificuldades e superamos novos obstáculos.
The input of organic matter in the soil by the no-tillage system (NTS) increases as the system becomes established, raising the levels of organic phosphorus (P) and reducing the P soil adsorption. This study evaluated the availability of organic and inorganic P in areas under different management systems and stages of adoption in the Cerrado. The data were analyzed as a completely randomized design, corresponding to: (1) an NTS after 5 years of its implantation (NTS5); (2) an NTS after 17 years of its implantation (NTS17); (3) a conventional tillage system more than 20 years old (CTS); (4) Native Cerrado (NC). There were five repetitions for all treatments. Depths of 0–5 and 5–10 cm were evaluated for the available P (P-avail), remaining P (P-rem), organic P (oP), and inorganic P (iP) forms extracted with Sodium bicarbonate (NaHCO3) (P-avail), Sulfuric acid (H2SO4) (moderately labile), and Sodium hydroxide (NaOH) (moderately resistant). The P from the sequential extractions accumulated at a depth of 0–5 cm, mostly in the organic form in the NTS17 and NC areas, demonstrating the contribution of the NTS to the conversion of the P reserve in the soil. The CTS treatment greatly accumulated P, especially in the inorganic form, indicating the non-conservationist characteristic of this system. The oP and iP contents in the soil were not affected by age of the NTS, which was similar to the NC. Our results show that the continuous input of organic matter deposited on the soil surface in the NTS17 increased the levels of organic and inorganic P, consequently providing greater availability of P in the soil for cultivated crops.
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