Fabrício Tondello Barbosa

Water erosion in no-tillage monoculture and intercropped systems along contour lines

A erosao hidrica e a principal causa das perdas de solo e agua, assim como de degradacao das areas agricolas. O objetivo deste trabalho foi quantificar a erosao hidrica pluvial em uma area sem preparo previo do solo, cultivada em contorno, em 2009 e 2010, sobre um Cambissolo Humico, com os seguintes tratamentos: milho solteiro, soja solteira, feijao solteiro e milho e feijao consorciados, submetidos a quatro testes de chuva simulada com intensidade constante de 64 mm h-1 e duracao de 1 h. O primeiro teste foi aplicado 18 dias apos a semeadura das culturas e, os demais, 39, 75 e 120 dias, apos o primeiro. O tipo de cultura influenciou a erosao hidrica nos testes 3 e 4 de chuva simulada; a soja foi mais eficaz no teste 3, enquanto, no teste 4, o milho foi mais eficiente no controle da erosao. As perdas de agua foram influenciadas pelo tipo de cultura apenas no teste 3, onde o milho e a soja demonstraram a mesma eficiencia, com menores valores de enxurrada do que as demais culturas. A taxa de perda de solo variou de distintas formas ao longo do periodo de amostragem da enxurrada, demonstrando relacao linear positiva entre as perdas de solo e as de agua, nos varios testes de chuva simulada.

Erosão hídrica em campo nativo sob diversos manejos: perdas de água e solo e de fósforo, potássio e amônio na água de enxurrada

Native pastures in southern Brazil are used for cattle and sheep grazing. The forage offer in the spring-summer season is greater than the animal requirement, so the forage left over is usually burned. Pasture burning mineralizes nutrients and leaves the soil bare, triggering water erosion. This study aimed to quantify total soil and water losses and P, K and NH4+ contents in the runoff water from an Oxisol with native pasture. In the treatments, the native pastures, were i) unburned and unfertilized, ii) unburned and P-fertilized, iii) burned and unfertilized, and iv) burned and P-fertilized. Rain was simulated at an intensity of 75 mm h-1 and duration of 3 h on the plots (11 m long along the slope and 3.5 m wide). Burning of the native vegetation decreased the times until runoff began and peaked and reduced soil water infiltration, but increased the maximum runoff rate, soil and water losses by water erosion and the P, K and NH4+ concentration and total losses in the runoff water, compared to no burning. The runoff sediment concentration was higher in the treatment with vegetation burning than without. The highest and lowest values of sediment concentration were detected after a shorter runoff period in the treatment with vegetation burning than in that without, which is related to the 8.9 times higher total soil loss from burnt than from unburnt grassland. The P concentration and total loss in the runoff water were higher in the treatment with than without phosphate fertilizer, in the treatment with burning as well as that without. For K and the NH4+ , the concentration and total losses were higher in the treatment with burning than in that without. Phosphorus, K and NH4+ concentration in the runoff water fit the exponential model y = ae-bx in relation to runoff duration (p < 0.01).

Water erosion in surface soil conditions: runoff velocity, concentration and D50 index of sediments in runoff

Water erosion and contamination of water resources are influenced by concentration and diameter of sediments in runoff. This study aimed to quantify runoff velocity and concentration and the D50 index of sediments in runoff under different soil surface managements, in the following treatments: i) cropped systems: no-tilled soil covered by ryegrass (Lolium multiflorum Lam.) residue, with high soil cover and minimal roughness (HCR); no tilled soil covered by vetch (Vicia sativa L.) residue, with high soil cover and minimal roughness (HCV); chiseled soil after ryegrass crop removing the above-ground residues and keeping only the root system, with high roughness (HRR); chiseled soil after vetch crop removing the above-ground residues and keeping only the root system, with high roughness (HRV); ii) bare and chiseled soil, with high roughness (BHR). The research was conducted on a Humic Dystrupept under simulated rainfall. The design was completely randomized and each treatment was replicated twice. Eight rainfall events of controlled intensity (65 mm h−1) were applied to each treatment for 90 minutes. The D50 index, runoff velocity and sediment concentration were influenced by crop and soil management. Runoff velocity was more intensely reduced by cover crop residues than by surface roughness. Regardless of surface condition, the D50 index and concentration of sediment in runoff were lower under ryegrass than vetch crop. Runoff velocity and the D50 index were exponentially and inversely correlated with soil cover by residues and with surface roughness, while the D50 index was positively and exponentially correlated with runoff velocity.