ABSTRACT Knowledge of the decomposition dynamics of aboveground phytomass and its release of nutrients in mixtures of cover crops as well as the impact on the soil tillage system is fundamental for the sustainable management of agroecosystems. This work aimed to evaluate whether soil tillage and the choice of cover crops cultivated in the interrows can be technological strategies to increase dry biomass production, increase the capacity to add carbon, and improve macronutrient cycling in a mango ( Mangifera indica L.) orchard in a semi-arid environment. The field experiment (sixth year) consisted of two soil tillage systems (NT-no tillage and CT-conventional tillage) combined with three plant mixtures (PM1-75 % leguminous + 25 % grasses and oilseed species, PM2-25 % leguminous + 75 % grasses and oilseed species, and SV - spontaneous vegetation). Phytomass production and nutrient accumulation were not affected by the soil tillage system, but PM1 had the highest phytomass production and accumulations of C, N, and K, and it was significantly superior to SV. Regardless of the type of plant mixture, cultivated or spontaneous, soil tillage increased the rates of phytomass decomposition and nutrient release evaluated for 315 days after the cover plant management. The PM1 had the highest rates of decomposition and release of P and K, followed by PM2 and SV. There was no difference between the mixtures for the release of N, Ca, and Mg. The use of a mixture of cover crops, regardless of the predominance of leguminous or non-leguminous species, and a no-tillage system were technological strategies that could be adopted to favor the addition of soil carbon and nutrient cycling in fruit agroecosystems in the Brazilian semi-arid region. Spontaneous vegetation, due to its capacity to accumulate nutrients and the recalcitrant characteristics of its phytomass, has the potential to cycle nutrients and keep the soil covered. In addition, spontaneous vegetation should be better investigated because it is a low-cost strategy in agroecosystem designs.

ABSTRACT Soil organic matter (SOM) plays a key role in maintaining the productivity of tropical soils, providing energy and substrate for the biological activity and modifying the physical and chemical characteristics that ensure the maintenance of soil quality and the sustainability of ecosystems. This study assessed the medium-term effect (six years) of the application of five organic composts, produced by combining different agro-industrial residues, on accumulation and chemical characteristics of soil organic matter. Treatments were applied in a long-term experiment of organic management of mango (OMM) initiated in 2005 with a randomized block design with four replications. Two external areas, one with conventional mango cultivation (CMM) and the other a fragment of regenerating Caatinga vegetation (RCF), were used as reference areas. Soil samples were collected in the three management systems from the 0.00-0.05, 0.05-0.10, and 0.10-0.20 m layers, and the total organic carbon content and chemical fractions of organic matter were evaluated by determining the C contents of humin and humic and fulvic acids. Organic compost application significantly increased the contents of total C and C in humic substances in the experimental plots, mainly in the surface layer. However, compost 3 (50 % coconut bagasse, 40 % goat manure, 10 % castor bean residues) significantly increased the level of the non-humic fraction, probably due to the higher contents of recalcitrant material in the initial composition. The highest increases from application of the composts were in the humin, followed by the fulvic fraction. Compost application increased the proportion of higher molecular weight components, indicating higher stability of the organic matter.