Pasture production, nitrogen responses and sheep liveweight gain from Caucasian and white clover pastures: a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

The autumn pasture production and liveweight gain (LWG) from Caucasian and white clover/ryegrass pastures, maintained at high and low soil fertility, were measured in a grazing experiment at Lincoln University, Canterbury. Caucasian clover pastures had 10% greater autumn/early winter dry matter production than white clover pastures (7840 c.f. 7120 kg DM ha⁻¹, P = 0.006). Total clover production from Caucasian clover pastures (total 2300 kg DM ha⁻¹) was 2.15 times greater than white clover pastures (P < 0.000). Although when compared to white clover, Caucasian clover pastures offered to lambs contained a greater pre-grazing clover content (20.5 c.f. 10.1%, P = 0.006), LWG head⁻¹ was similar on both pastures (Caucasian clover 109 g hd⁻¹ d⁻¹, white clover 80 g hd⁻¹ d⁻¹, P = 0.373). A higher stocking rate was sustained on high compared to low fertility farmlets (39.9 c.f. 37.5 lambs ha⁻¹, P = 0.058), also there were 24 more grazing days (490 c.f. 466 grazing days, p = 0.034) on high fertility pastures even though LWG ha⁻¹ was similar (high fertility 3.76 kg ha⁻¹ d⁻¹, low fertility 3.56kg ha⁻¹ d⁻¹, P = 0.871).

In another experiment, the response of Caucasian and white clover based pastures, at high and low soil fertility, to the autumn application of nitrogen (120 kg N ha⁻¹) was evaluated to establish the suitability of Caucasian clover in dairy pastures. The application of N increased pasture production by 3.5-3.9 kg DM ha⁻¹ kg N⁻¹ (p = 0.285, 0.228), less than the commonly expected response of 10 kg DM ha⁻¹ kg N⁻¹. Pasture clover content was not affected by N application at any harvest (0.283 < P < 0.786). However, total clover production was 2.15 times greater in Caucasian clover compared to white clover pastures (2300 c.f. 1080 kg DM ha⁻¹, P < 0.000). Chemical analysis of the grass components indicated that the application of 420 kg N ha⁻¹ over the previous 12 months had increased the mean N content in ryegrass (3.98 c.f. 3.70%, P < 0.000) and annual grass (4.48 c.f. 4.16%, p = 0.026) compared to plots that did not receive N. The lack of response to the applied N was attributed to a number of factors including the short defoliation interval (22 days), the availability of mineralised N from the fertile soil after four years of N₂ fixation, annual grass content of the pasture (22-28%) and mealy bug infestation in ryegrass.

In a third experiment, the success of transplantation of Caucasian clover seedlings into two dairy pastures in autumn 1998, three years previously, was evaluated to determine whether Caucasian clover can survive and spread under dairy farm management and N inputs. Of the Caucasian clover plants that were transplanted, approximately 30% had survived until autumn 2001. The mean plant diameter of the surviving plants was 106 mm and 182 mm in paddocks with and without regular N fertiliser application, respectively. Total visual clover cover in early May was 19-47% where Caucasian clover seedlings had been transplanted and 15-31% at an adjacent site.

These short-term studies were inconclusive in showing that increased legume content and total dry matter production from Caucasian clover pastures will lead to increased animal productivity. However, even in a high N environment (420 kg N ha⁻¹ yr⁻¹), Caucasian clover pastures produced more total legume than white clover pastures, and a long-term study to determine the suitability of Caucasian clover for dairy pastures is warranted.