Nitrate-nitrogen reduction by established tree and pasture buffer strips associated with a cattle feedlot effluent disposal area near Armidale, NSW Australia
Vegetated buffer strips have been recognized as an important element in overall agro-ecosystem management to reduce the delivery of non-point source pollutants from agricultural land to inland water systems. A buffer strip experiment consisting of two tree species ('Eucalyptus camaldulensis' and 'Casuarina cunninghamiana') with two planting densities and a pasture treatment was conducted to determine the effectiveness of NO₃-N removal from a cattle feedlot effluent disposal area at Tullimba near Armidale, NSW Australia. Different management methods were applied for the buffers where grass and weeds were mowed 2-3 times during the second and third years and were not managed during the rest experimental years for the tree buffer, while grass was harvested 1-3 times per year for the pasture buffer. The differences between tree species and planting density significantly affected tree growth, but the growth difference did not significantly affect their capacities to reduce NO₃-N in soil surface runoff and groundwater. On average for all the tree and pasture treatments, the buffer strips reduced NO₃-N concentration by 8.5%, 14.7% and 14.4% for the surface runoff, shallow and deep groundwater respectively. The tree and pasture buffer strips were not significantly different in NO₃-N reduction for both shallow and deep groundwater while the pasture buffer strips reduced significantly more NO₃-N concentration in surface runoff than the tree buffer strips. Both buffer strips reduced more than 50% of surface runoff volume indicating that both the tree and pasture buffer strips were efficient at removing water and nutrients, mostly through a significant reduction in soil surface runoff volume.
Periodic rest from grazing provided no control of an invasive perennial forb
This study examined if one grazing strategy (namely seasonal rest) was effective in the control of the invasive forb 'Phyla canescens' (Kunth) Greene (hereafter lippia). We examined if rest from grazing could increase the competitiveness of native palatable species by allowing time to recover from defoliation, thereby altering competitive interactions between native species and lippia. In a field trial, we manipulated cattle grazing to determine its effects on the biomass of lippia and native species. We compared rest from grazing at different times of the year with year-long grazing (low intensity continuous and high intensity short duration) and no grazing (permanently excluding large grazing animals). Experimental plots were stratified into different hydrological areas (approximately annual flooding and flooded less than once every 5 years) to include flood dynamics in the management scenarios. We detected no negative impacts of seasonal rest on lippia, but some positive effects on native species. We found that complete exclusion from grazing in areas that already have substantial lippia invasion (and no flooding) may actually favour the expansion of lippia (at certain times). This study does not suggest that grazing management cannot be used as a tool for lippia control - simply that seasonal resting had no effect over a 3-year period. This is likely due to the dynamics of a boom-and-bust landscape in which if the abiotic conditions are not suitable for growth, then native species will not grow whether grazed or rested.