Annual yield and botanical composition of four dryland grass species with or without nitrogen over six years

Abstract

Nitrogen (N) and water availability affect pasture production and persistence. Yield and botanical composition of four monocultures of brome (BR), cocksfoot (CF), perennial ryegrass (RG) and tall fescue (TF) were evaluated with (+N) or without (-N) N at Ashley Dene farm, Canterbury, over six growth seasons from establishment in 2014/15 (Year 1) to 2019/20 (Year 6). Total annual yields ranged from 2.04 (RG-N; Year 1) to 12.7 t DM/ha/yr (CF+N; Year 3). Yields differed among species in Years 1, 3, 4 and 6 when TF pastures had the lowest production. There was no difference in DM production from BR, CF and RG pastures. Additionally, +N pastures produced ~55% more yield than –N pastures in Years 3 and 5 when spring/summer rainfall was adequate to maintain growth. Sown grasses accounted for >89% of total DM yield in Years 1 and 2 but the proportion of total annual DM production from sown species declined from Year 3. By Year 6, sown species accounted for 48±3.3 (TF) to 64±3.3% (BR, CF and RG) of total annual DM production. Generally, TF failed to perform in this dryland environment. In contrast, the production and persistence of the other three species were not different when subjected to water deficits alone.