Initial studies of the growth, nitrogen sequestering, and de-watering potential of perennial grass selections for use as nitrogen catch crops in orchards

Abstract

Two field trials were established to evaluate the ability of perennial grasses to recoup leaching losses of nitrogen in orchards. A perennial grass was considered suitable for use in orchards if it had a winter active–summer dormant growth cycle. High winter growth would ensure de-watering of the soil profile and nitrate uptake during this period, when an orchard is most vulnerable to leaching losses of nitrate. Low growth in summer would minimise competition for water and nutrients with fruit trees. These traits were studied in 14 varieties of grasses from 8 species in an open field and in an established apricot orchard. Semi-dormant summer growth was observed in species such as Dactylis glomerata L. cv. Kasbah, and Festuca arundinacea L. cv. MK88931. In the open field trial, the sequestration of NO₃^–-N + NH₄⁺-N between late autumn and early spring, by Kasbah and MK88931, was estimated at 172 and 220 kg N/ha, respectively. Kasbah and MK88931 also demonstrated the driest soil profiles to a depth of 1.5 m in this period. This reflected their high water use and de-watering potential. Therefore, the performance of these grasses demonstrated a model approach to mitigate nitrate leaching below orchard root-zones. They could minimise deep percolation of rainfall and sequestered large amounts of inorganic nitrogen in soil during winter, whilst producing low growth during summer.