Productivity and quality of a perennial ryegrass pasture treated with controlled release

Abstract

The objective of this study were to assess the productivity and quality of a perennial ryegrass pasture treated with controlled release urea. Maintaining pasture production with conventional urea fertilizer results in high leaching losses to the environment. Alternatives such as controlled release urea have the potential to maintain production and lessen environmental impact. Therefore, two experiments were conducted using perennial ryegrass (Lolium perenne) treated with conventional urea (U) against polymer coated urea (CR).

Experiment 1 was conducted as a field trial on a perennial ryegrass pasture, with six harvests from plots treated with split applications of 150kg N/ha-1 yr-1 of (CR150), 150kg N/ha-1 yr-1 (U150) or 200kg N/ha-1 yr-1 of (U200) and 0kg N/ha-1 yr-1 as the control. Experiment 2 was conducted at the glasshouse using pasture trays of perennial ryegrass with a single application at rates of 0 (control), 50, 100, 150, 200, 300 or 400kg N/ha of CR and U, pasture trays were grown outdoors for 6 weeks and were then moved to the glasshouse. Under field conditions, U200 produced the highest DM, CR150, and U150 were intermediated and statistically similar for 4 harvests (Nov, Jan, Mar and Apr), the control always produced the lowest. The water % of perennial ryegrass grown in the field was variable for all harvests. Crude protein (CP) concentrations were similar for U150 and CR150 for 4 harvests (Mar, April, May and July). Neutral detergent fibre (NDF), and dry matter digestibility (DMD) had no consistent effect with N treatments, and metabolisable energy (ME) was not significant throughout all harvests. Experiment 2 outdoors indicated that CR rates were unable to match growth that of U, while growth in the glasshouse resulted in an overlap of the 2 fertilizer types.

It is likely that moisture and temperature conditions limit use of CR fertilizer. The beginning lag-phase of CR was successfully countered by with a 50/50 application of conventional (U) and coated urea (CR). Perennial ryegrass treated with CR required favourable conditions to match productivity and quality of conventional urea, this was indicated by DM production and CP concentrations. Therefore, if CR fertilizer is used as an alternative to conventional urea, lag phase, and climate should be taken into account by the management of the system.