The effect of lime and nitrogen fertiliser on growth and botanical composition of pasture converted out of Pinus radiata forest: A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science at Lincoln University

Abstract

The effect of lime and nitrogen application rate on pasture growth and botanical composition was investigated on a former forestry site located on the Canterbury plains at Darfield ( 43°8'S, 172° 8'E, 185 m.a.s.l). The objective of the trial was to examine the effects of nitrogen and lime on pasture production, pasture botanical composition, and to subsequently provide recommendations to farmers undertaking pine forest to pasture conversions. The site when converted was found to have a low soil pH of 4.8 and a high C: N ratio of - 15- 27: 1 resulting in very low levels of essential plant nutrients including nitrogen. The treatments were 0, 2.5, 5, and 10 t/ha of standard agricultural lime and nitrogen at five rates of 0, 50, 100, 200 and 400 kg N/ha, laid out in a factorial split-plot design with lime as the main factor and nitrogen as sub-plots. In 2005 one side of the trial was sown in a permanent dryland pasture mix while the other side was sown into triticale (x tritisecale wittmack) before being unsown with a permanent pasture mix. Monitoring of these pastures have been carried out every year since the start of the trial in terms of pasture production, pasture botanical composition and soil tests. Over the 204 day trial period pasture plots applied with 0, 50, 100, 200, and 400 kg N/ha had total dry matter (DM) yields of 2095, 2468, 2807, 3427, and 3445 kg DM/ha respectively. Both the dryland pasture compared and results showed that the triticale side produced 3054 kg DM/ha which was 411 kg DM/ha more than the pasture side which yielded 2643 kg DM/ha. N use efficiency over the entire growth period was highest for the 50 kg N/ha treatment at 21.8 kg DM/kg N which declined linearly to 4.4 kg DM/kg Nat 400 kg N/ha . Pasture botanical composition was decreased as result of nitrogen application. White cloverpresence was reduced by 10% at the 0 kg N/ha treatment to the 400 kg N/ha rate. This was consistent with the triticale side where the 400 kg N/ha treatment reduced clover presence by 9 and 3% for red and white clovers respectively. Chicory and Plantain however, showed an increase in existence as nitrogen rate increased towards 100 kg N/ha, although presence began to declined at the high nitrogen rate of 400 kg N/ha. Liming of the soil did not have any significant effect on subsequent pasture production. However white clover population was increased from 1.32% to 5.61 % while subterranean clover was increased from 0.67 to 1.14% from 0 t/ha to 1 0t/ha on the pasture side. Lime rate was also shown to have an effect on legume population on the triticale side which saw an increase of 6% in white clover. Red clover increased from 7% at the 0 t/ha lime treatment to 16% at the 10 t/ha treatment. Weed species such as browntop decreased within the sward with lime application rate. 10 t/ha of lime reduced browntop by 1 % on the pasture side. On the triticale side browntop was reduced on average by 16% at the highest lime treatment of 10 t/ha. Therefore it is suggested that although lime did not have a substantial effect on pasture production it did increase legume abundance which is critical in driving high production from these low nitrogen sites in future years. This study concludes that heavy inputs of nitrogen are required for acceptable pasture production on a former forestry plot and to assist with the degradation of woody debris. Liming of the soil did not have any significant effect on pasture production but however had a pronounced effect on legume abundance and weed invasion which increased the quality of the subsequent pasture sward.