Comparative productivity of irrigated short-term ryegrass (Lolium multiflorum) pasture receiving nitrogen, grown alone or in a mixture with white (Trifolium repens) and Persian (T. resupinatum) clovers

Abstract

Dairy farms in subtropical Australia use irrigated, annually sown short-term ryegrass (Lolium multiflorum) or mixtures of short-term ryegrass and white (Trifolium repens) and Persian (shaftal) (T. resupinatum) clover during the winter–spring period in all-year-round milk production systems. A series of small plot cutting experiments was conducted in 3 dairying regions (tropical upland, north Queensland, and subtropical southeast Queensland and northern New South Wales) to determine the most effective rate and frequency of application of nitrogen (N) fertiliser. The experiments were not grazed, nor was harvested material returned to the plots, after sampling. Rates up to 100 kg N/ha.month (as urea or calcium ammonium nitrate) and up to 200 kg N/ha every 2 months (as urea) were applied to pure stands of ryegrass in 1991. In 1993 and 1994, urea, at rates up to 150 kg N/ha.month and to 200 kg N/ha every 2 months, was applied to pure stands of ryegrass; urea, at rates up to 50 kg N/ha.month, was also applied to ryegrass–clover mixtures. The results indicate that applications of 50–85 kg N/ha.month can be recommended for short-term ryegrass pastures throughout the subtropics and tropical uplands of eastern Australia, irrespective of soil type. At this rate, dry matter yields will reach about 90% of their potential, forage nitrogen concentration will be increased, there is minimal risk to stock from nitrate poisoning and there will be no substantial increase in soil N. The rate of N for ryegrass–clover pastures is slightly higher than for pure ryegrass but, at these rates, the clover component will be suppressed. However, increased ryegrass yields and higher forage nitrogen concentrations will compensate for the reduced clover component. At application rates up to 100 kg N/ha.month, build-up of NO3–-N and NH4+-N in soil was generally restricted to the surface layers (0–20 cm) of the soil, but there was a substantial increase throughout the soil profile at 150 kg N/ha.month. The build-up of NO3–-N and NH4+-N was greater and was found at lower rates on the lighter soil compared with heavy clays. Generally, most of the soil N was in the NO3–-N form and most was in the top 20 cm.

Effect of biochar amendment on the soil-atmosphere exchange of greenhouse gases from an intensive subtropical pasture in northern New South Wales, Australia

“…Annual ryegrass (Lolium multiflorum) is one of the main species for winter grazing in these systems, with high applications of N-fertilizer. Lowe et al (2005) recommended that 50-85 kg N ha −1 month −1 be applied to annual ryegrass during the winter months to maintain high productivity. Due to the combination of high fertilizer rates, high rainfall events and temperatures throughout the year, elevated emissions of N 2 O can be expected.…”

Fate of fertiliser nitrogen in a ryegrass–kikuyu dairy pasture system

“…The response to N applied was high and similar to the range reported by Lowe et al . (2005) of 5–28 kg DM kg −1 N ha −1 in annual ryegrass and Billingham (2015) of 13–27 kg DM kg −1 N ha −1 in kikuyu, which is likely due to the experimental site being irrigated as opposed to rainfed. However, the amount of cow urine N contributing to pasture growth, which can range from 125 to 250 kg N ha −1 year −1 (Whitehead 1986), and marginal N response (Staines et al .…”