In the SE periphery of Brazilian Amazonia, low-input agriculture systems on sandy loam soils have very low nutrient use efficiency. In a low-input alley cropping system, we measured residue decomposition dynamics and the yield and nutrient uptake of a maize crop associated with the following treatments: Clitoria + Pigeon pea; Acacia + Pigeon pea; Leucaena + Clitoria; Leucaena + Acacia, Leucaena + Pigeon pea and no residue input (control). The acacia treatments provided better soil coverage throughout the whole corn cycle. Potassium was released faster than nitrogen from the residues; N concentration in corn leaves in the residue treatments were below critical levels. The Leucaena + Acacia treatment was the most effective in increasing posttasseling N and K assimilation and K use efficiency.This resulted in corn productivity 3.5 times greater (7.3 Mg ha −1 ) than the control without residue application. In the Amazonian sandy loam soils, which are susceptible to hardsetting and nutrient leaching, efficient N and K use should be priorities for soil management. Although no-till alley cropping of leguminous trees constitutes an important option for lowinput farming, its efficiency depends on using a mixture of residues that keeps soil covered and have high rates of both N and K release during the entire crop cycle.

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Alley cropping has been considered a means of intensifying land use sustainably as an alternative to slash and burn agriculture in tropical regions. An experimental trial was used to evaluating the growth and productivity of corn under alley cropping to test the viability of this system as a sustainable land use practice in an amazonian Ultisol. The experimental layout was a completely randomized block design with four replications of six treatments: mulch with 13.4 and 8.9 t ha -1 of pigeon pea, and a control treatment without mulch of pigeon pea, with or without tillage. Sustainability of soil and crop were determined from changes on physical properties, such as total porosity, air capacity, available water capacity of the soil, net assimilation rate, crop growth rate, and leaf area index, as well as several productivity parameters, including average weight of ears, weight of 100 grains, and total dry matter. Both mulching and tillage increased the air capacity. Mulching of tilled areas protects the soil against the rainfall impact and prevented its recompaction. The reduced air capacity of the soil had a negative impact on the net assimilation rate, resulting in lower productivity in the no-mulch and no-till plots, mainly due to the reduction of grain weight.

The unsustainable use of the soil of the deforested area at the Amazonian border is one of the greatest threats to the rainforest, because it is the predominant cause of shifting cultivation in the region. The sustainable management of soils with low natural fertility is a major challenge for smallholder agriculture in the humid tropics. In the periphery of Brazilian Amazonia, agricultural practices that are recommended for the Brazilian savannah, such as saturating soils with soluble nutrients do not ensure the sustainability of agroecosystems. Improvements in the tilled topsoil cannot be maintained if deterioration of the porous soil structure is not prevented and nutrient losses in the root zone are not curtailed. The information gleaned from experiments affirms that in the management of humid tropical agrosystems, the processes resulting from the interaction between climatic factors and indicators of soil quality must be taken into consideration. It must be remembered that these interactions manifest themselves in ways that cannot be predicted from the paradigm established in the other region like the southeast of Brazil, which is based only on improving the chemical indicators of soil quality. The physical indicators play important role in the sustainable management of the agrosystems of the region and for these reasons must be considered. Therefore, alley cropping is a potential substitute for slash and burn agriculture in the humid tropics with both environmental and agronomic advantages, due to its ability to produce a large amount of residues on the soil surface and its effect on the increase of economic crop productivity in the long term. The article presents some promising patents on the importance of an alternative for sustainability of agriculture.