Structural architecture and functioning of an alfisol after 17 years of organic fertilization in no-till cropping

Abstract

Using animal manure as fertilizer is an alternative adopted in Brazilian agricultural farms, especially where there is integrated production of animals and crops. Nevertheless, the longterm impacts of continuous application of different organic and inorganic fertilizers on the structural organization, functionality and internal strength remains poorly investigated, especially in subtropical climatic conditions. This information is valuable to identify potential risks and benefits of each management. We investigated how 17 years of continuous application of animal manure and mineral fertilizers in successive crops under no-till farming system affected the structure of a sandy soil (Hapludalf), in terms of microstructural stability and resistance (Chapter 1), organization and stability of aggregates, and pore functionality for water retention and air flow (Chapter 2). The study was developed in a long-term experiment in southern Brazil, implemented in 2004 in a randomized block design with four repetitions. The treatments consisted of the application of different organic and inorganic fertilizers in successive crops under no-till farming system: pig slurry (PS), cattle slurry (CS) and pig deep litter (PDL), mineral fertilizer (MF) and no fertilizer application - control (CL). Soil samples with and without preserved structure were collected in the layers of 0-5 and 5-15 cm for soil chemical characterization, evaluation of physical properties of capacity and pore functionality, microstructural resistance and viscoelasticity under oscillatory shear, aggregate stability, and intra-aggregate pore geometry using x-ray computed tomography. The long-term application of fertilizers led to distinct changes in soil microstructural resistance and viscoelasticity under oscillatory shear, as well as aggregation and pore functionality. PDL and CS application increased the soil elastic deformation range, however, only the PDL fertilizer increased the shear strength in this range. The PS and MF fertilizers reduced the soil microstructural stability under saturated conditions, while the PDL fertilizer reduced the soil susceptibility to oscillatory shear. The PS, MF, and CS fertilizers decreased the proportion of water-stable macroaggregates, mainly in the 5-15 cm layer. Moreover, treatments with higher root activity and higher carbon input to the soil provided the formation of aggregates with a more connected and complex pore network, and with long and continuous pore channels. Pore size distribution and pore functionality for water retention and air flow were also affected by fertilizer management, especially in the 0-5 cm layer. PDL fertilizer application significantly increased soil water retention and air permeability compared with the other fertilizers applied. Overall, our findings highlight the importance of adding organic matter to the soil through fertilizers and the contribution of surface residues for the development, stability, and pore functionality of sandy soils in subtropical climates.