No-tillage and manure applications increase aggregation and improve nutrient retention in a sandy-loam soil

Soil aggregation plays a crucial role in soil physicochemical and biological processes, thus influencing soil nutrient retention. It is possible to improve soil aggregation by choosing appropriate agricultural practices. The objective of this study was to evaluate the effects of tillage, crops and fertilizer sources on size distribution of water-stable aggregates (WSA) and nutrient concentrations in aggregate fractions. Soil samples were collected from field sites involving sixteen factorial combinations of tillage [conventional tillage (CT) or no-till (NT)], crop rotations [continuous maize (CC) or soybean/maize (SC)] and fertilizer sources (0, 15, 30 and 45 Mg wet weight ha(-1) of composted cattle manure balanced with inorganic fertilizers). Aggregate fractionation was performed using a wet-sieving method. Four years after the treatments were established, the proportion of large WSA (WSA(> 2mm)) was greater in the NT system, suggesting that NT increased soil aggregation compared to the CT system. There was no difference in soil aggregation between continuous maize and soybean/maize rotations. The application of 30 and 45 Mg ha(-1) year 1 of composted manure produced more WSA(> 2mm) than inorganic fertilizers. The WSA(> 2mm) had a higher total C concentration in CT than NT soils, indicating that WSA(> 2mm) formed in CT systems contained more soil organic matter (SOM) than those in NT systems. However, the difference disappeared when the data were expressed on a sand-free aggregate basis, indicating a dilution effect due to more sand in WSA(> 2mm) from the NT system than the CT system. Total C, N and P concentrations were at least 3 times higher in water-stable microaggregates (WSA(0.25-0.053mm)) than water-stable macroaggregates (WSA(> 0.25mm)). The WSA(0.25-0.053mm) fraction is considered to be a sink for these nutrients, but may also be susceptible to erosion. Transport processes that preferentially remove the WSA(0.25-0.053mm) fraction from agroecosystems could lead to nutrient loading in adjacent ecosystems. It was concluded that adopting no-tillage and applying composted manure increased soil aggregation and nutrient retention in a sandy-loam soil under maize production. (c) 2005 Elsevier B.V. All rights reserved.