The effect of defoliation severity during late autumn on herbage production, regrowth and nitrogen uptake of diverse pastures in Canterbury, New Zealand

Grace S. Cun*, Grant R. Edwards, Racheal H. Bryant

Faculty of Agriculture and Life Sciences, Lincoln University, Lincoln 7647, Christchurch

*Corresponding author email: [email protected]

Abstract

Pasture management strategies are sought to reduce nitrate leaching by enhancing nitrogen (N) uptake over the winter period. The objective of this study was to determine the effect of five post grazing heights on herbage production, and N uptake of a diverse pasture mixture containing perennial ryegrass, white clover, chicory, plantain, and lucerne during the late autumn/winter season. In late autumn, pastures were defoliated to five residual heights (20, 30, 40, 50, 60 mm), and herbage dry matter (DM) and N accumulated over a 112 d regrowth period was measured. Swards defoliated to 20, 30 and 40 mm accumulated more herbage above ground level (1884, 1508, 1322 kg DM/ha, respectively) than those defoliated to 60 mm (1289 kg DM/ha) over 112 days. Repeated measures analysis on herbage N concentration showed a significant interaction (P=0.012) of defoliation treatment with time. For the 20 mm defoliation, N concentration increased over time from 18.8 to 29.7 g N/kg while for the 60 mm defoliation, decreased from 26.1 to 24.9 g N/kg during the regrowth period. During this 112 d regrowth period, pastures defoliated to 20 mm accumulated more DM and more N than plots defoliated to 60 mm (56 vs. 32 kg N/ha, respectively). The results indicate grazing severely to post grazing heights <40 mm may improve growth and N uptake in the late autumn/winter.