In tropical regions with well‐defined wet and dry seasons, repeated wetting and drying cycles can harden exposed soils and inhibit root growth. While this phenomenon has been well documented, the relationships between plant productivity and chemical and physical soil parameters have not been well defined. The current study identifies the abiotic parameters that best relate to measures of plant development, specifically to corn productivity. The primary goal of this research was to provide information to improve agricultural sustainability in humid tropical ecosystems. The effects of using plant residues as a cover on a sandy soil were studied. Four leguminous species were planted in an alley cropping system, Leucaena leucocephala, Cajanus cajan, Clitoria fairchildiana and Acacia mangium, and corn was planted in January 2007 between legume rows. We measured the most important chemical and physical soil parameters. Yield indicators included cob weight and the weight of 100 kernels. The application of plant residues altered soil conditions and increased rootable soil volume. This change was associated with an increase by 10% in water retention above field capacity in the uppermost soil layer of the residue‐covered sections of the experiment. In the control sections cobs were up to three times lighter (31.43–93.38 g) in the bare soil control than those from residue‐covered sections of the experiment. Dynamic indicators related to nutrient absorption and crop evapotranspiration, such as the number of days with water stress and rootable soil volume, were the most suitable indicators for assessing soil quality. The response of corn was best related to complex physical indicators, including the amount of N applied via legume residues.

The efficiency in the use of nitrogen (N) and potassium (K) may be severely limited in soils with high rates of nutrient loss and that also tend to harden and restrict root growth. The choice of legume residues should take into account the nutrient supply and the need for soil improvement. We assessed the capacity of alley cropping systems to enhance root development, increase nutrient uptake and improve the use of N and K in maize. The experiment included six treatments with residues of four perennial Fabaceae: Clitoria + Gliricidia (C + G); Acacia + Gliricidia (A + G); Leucaena +Gliricidia (L + G); Leucaena + Clitoria (L + C); Leucaena + Acacia (L + A) and a control without legumes. We determined chemical and physical indicators, root length density (RLD) and an efficiency index. The results demonstrate the effects of amending soils with N and K with root growth constrained by hard‐setting. The application of combined residues improved the physical properties of hard‐setting soils and increased basic cations in the topsoil. A combination of residues with N and K fertilizer increased the maize yield. The relative efficiency and RLD in the L + A treatments were highest as a result of increased application through the residues containing N and K. The choice of residues for hard‐setting soils should take into account the supply of nutrients as well as the improvement of soil properties.

RESUMO -Este trabalho teve por objetivos identificar e avaliar a agressividade potencial das plantas dan inhas em um agrossistema com leguminosas herbáceas anuais como cobertura de solo. Foram plantadas, nas ruas de um sistema de aléias de sombreiro ( Clitoria fairchildiana) e no final do período agrícola, as leguminosas mucuna-preta, feijão-guandu, feijão-de-porco e calopogônio, em sistema de blocos ao acaso com cinco repetições. Para est udo da din âmica da com posiç ão flo rís tic a, avali aram-se a fre qüência , densida de, dominância, similaridade, diversidade de espécies e biomassa das plantas daninhas. Foram identificadas 42 espécies de plantas espontâneas, das quais as mais freqüentes e de maior densidade e dominância foram Leptochoa virgata, Panicum laxum e Sidasp. Não foram detectadas diferenças significativas para densidade, número de espécies, diversidade e biomassa entre as plantas daninhas emergidas nos quatro tratamentos com leguminosas; nem destas em relação ao controle.Palavras-chave: sistema em aléias, cultura de cobertura, dinâmica populacional. ABSTRACT -This study evaluated the efficiency of cover legumes in suppressing weed. A field experiment was arranged in a randomized block design with five replications in an alley

In humid tropical areas, a combination of factors related to soil conditions for root development contribute to decreased nutrient use efficiency. Our aim was to evaluate the combined effects of the application of gypsum and mulch from leguminous trees on rootability of root zone soil, root growth, phosphorus recovery efficiency and maize yield in a sandy loam soil prone to hardsetting. The experiment involved a randomized block design with four replications and six treatments: no residue or gypsum (control, C); leguminous residues (L); leguminous residues and 6 t/ha of gypsum (LG6); urea and 6 t/ha of gypsum (UG6); leguminous residues, urea and 6 t/ha of gypsum (LUG6); and leguminous residues, urea and 12 t/ha of gypsum (LUG12). Application of gypsum plus leguminous residues enhanced soil rootability, when applied to a tropical Arenic Hapludult, through the combined effects of increased porosity and decreased penetration resistance. These improvements facilitated root growth in deeper soil layers and greater nutrient uptake. Application of leguminous residues increased the input and retention of calcium in deeper layers. The use of large amounts of gypsum with leguminous residue, despite a significant increase in phosphorus uptake, did not result in a proportional increase in maize yield. Given the small differences in calcium content between the 6 and 12 t/ha gypsum treatments, applying a low dose of gypsum combined with leguminous residue, rather than administering a single large gypsum dose, is recommended for tropical sandy loam soils with low cation retention capacities.

In weathered tropical soil, low nutrient use efficiency can lead to agricultural systems becoming unsustainable. Therefore, tropical agriculture is highly dependent on ecosystem services, such as nutrient recycling and carbon sequestration, to enhance soil fertility, increase nutrient uptake, and facilitate sustainable production of agricultural goods. This research aimed to find the balance between sustainability and profitability of tropical agriculture by evaluating the changes in soil caused by the ecosystem services provided by the biomass of leguminous trees (Gliricidia) and assessing how these changes (associated with potassium) can affect nitrogen‐use efficiency and maize yield. An experiment was conducted testing the impact of Glircidia biomass addition vs. bare soil, with or without addition of both nitrogen and/or potassium. Changes in soil organic matter, (SOM) base cations sum, soil resistance, N uptake, N‐use efficiency, and maize yield were evaluated. Gliricidia biomass, when used with N and K, contributed to increasing SOM by 5.0 g/kg and the sum of base cations by 1458. 65 kg/ha in the 0–30 cm layer. Moreover, grain yield was increased by approximately 70% in the treatments with Gliricidia when compared to treatments without biomass where yield was very low. In bare soil, the additional yield of 1.5 tons/ha would not be enough to convince farmers to change slash and burn to conventional bare soil systems. Our results showed that leguminous trees, such as Gliricidia, might contribute to ensuring sustainable agricultural intensification in humid tropical soils with low natural fertility by providing ecosystem services such as biomass production, carbon sequestration, base cation recycling, and increased N acquisition. These findings might be an important strategy to replace the common slash‐and‐burn‐system and preserve the rainforest against the traditional shifting cultivation system. In contrast, the conventional system with bare soil showed that the addition of nitrogen was unfeasible, mainly in conditions of high rainfall precipitation. In these circumstances, the use of potassium may increase nitrogen‐use efficiency only when biomass is not used.