Organic matter amendments to soil can reduce nitrate leaching losses from livestock urine under simulated fodder beet grazing

Abstract

This research tested the hypothesis that incorporation of Carbon-Rich Organic Matter Amendments (CROMA) into bare soil after winter forage grazing would immobilise urinary-nitrogen (N) and reduce nitrate-N (NO₃⁻-N) leaching losses. In mid-winter (14 July 2016), 32 intact soil monolith lysimeters (500 mm diameter and 700 mm deep) received natural cow urine at the equivalent rate of 300 kg N ha⁻¹, and CROMA treatments of either: (i) no CROMA (control), (ii) three rates of barley straw [2, 4 or 8 t carbon (C) ha⁻¹; C/N ratio of 66:1], (iii) two rates of separated dairy effluent solids (2 or 4 t C ha⁻¹; C/N ratio of 31:1), or (iv) two rates of spent woodchip bedding material (2 or 4 t C ha⁻¹; C/N ratio of 29:1). Leaching was measured for periods of approximately 100 days after treatment (250 mm of leachate collected). Across all treatments, 98–99% of the N leached was in the form of NO₃⁻-N. Incorporated barley straw and effluent solids were effective in reducing NO₃⁻-N leaching losses by up to 25% compared to the control treatment. Spent woodchip bedding was shown to be ineffective, which was attributed to a high lignin content.