Abstract
ABSTRACT - The aim of this study was to assess the organic matter changes in quantity and quality, particularly of the humic fraction in the surface layer (0-20 cm), of a Typic Plinthustalf soil under different management of plant mixtures used as green manure for mango (Mangifera indica L.) crops. The plant mixtures, which were seeded between rows of mango trees, were formed by two groups of leguminous and non -leguminous plants. Prior to sowing, seeds were combined in different proportions and compositions constituting the following treatments: 100% non-leguminous species (NL); 100% leguminous species (L); 75% L and 25% NL; 50% L and 50% NL; 25% L and 75% NL; and 100% spontaneous vegetation, considered a control. The plant mixtures that grew between rows of mango trees caused changes in the chemical composition of the soil organic matter, especially for the treatments 50% L and 50% NL and 25% L and 75% NL, which increased the content of humic substances in the soil organic matter. However, the treatment 25% L and 75% NL was best at minimising loss of total organic carbon from the soil. The humic acids studied have mostly aliphatic characteristics, showing large amounts of carboxylic and nitrogen groups and indicating that most of the organic carbon was formed by humic substances, with fulvic acid dominating among the alkali soluble fractions.
Highlights
The total organic carbon content (TOC) is usually low in tropical soils of semiarid regions, often not exceeding 10 g kg-1 soil mass (SALCEDO; SAMPAIO, 2008)
The plant mixtures used between rows in the mango cultivation induced a reduction in TOC in all treatments compared to the control (SV), with the exception of the 75% L and 25% non-leguminous species (NL) treatment (Table 3)
This decrease was in the order of 7–28% of the composition according to the plant mixtures
Summary
The total organic carbon content (TOC) is usually low in tropical soils of semiarid regions, often not exceeding 10 g kg-1 soil mass (SALCEDO; SAMPAIO, 2008). Irrigated crops in the Brazilian semiarid region can accelerate the decomposition of organic matter (OM) and may change the quality and quantity of the humified fractions of soil OM (CUNHA et al, 2009a). The humic fractions form an essential part of OM and are operationally defined on the basis of solubility in aqueous alkalis or acids. Since the majority of OM is formed by the humified fraction, its association with soil fertility (KONONOVA, 1982) and its use as an indicator of soil quality (ORLOV, 1998) are common. The relationships of humic acid (HA)/fulvic acid (FA) and humin (H)/TOC can express the relative degree of humification of the OM of soil and its lability
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