The effect of cropping sequences and nitrogen fertilizer on pasture production, botanical composition and soil health of a dryland site converted out Pinus radiata forest : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

The effect of different cropping sequences and nitrogen fertiliser was investigated on a former forestry site at Darfield, on the Canterbury Plains. The objectives were: to investigate the influence of N fertiliser and different cropping sequences on the productivity and botanical composition of recently-established pasture on a former forestry site characterised by acidic soil conditions and low soil fertility; investigate the abundance of weed (gorse) and, investigate specific soil chemical properties (pH, Olsen-P, Ca, Na, Mg and K) using soil test analysis and triticale (X Triticosecale Wittmack) as indicator of biological activity. Significant effects of cropping sequences on botanical composition were found. Triticale Brassica Pasture and Triticale Pasture Pasture cropping sequences produced the greatest total clover component at 48 % and 45% respectively. Ryegrass % cover was different in each of the cropping sequence (CS) treatments (P< 0.001) apart from Pasture Pasture Pasture and Grass Grass Grass treatments (at both low and high N). Both had a mean value of 74 % ryegrass. Cropping sequence treatments Fallow Pasture Pasture, TPP and TBP had lower values compared to PPP and GGG at 54, 34 and 1.5 % ryegrass respectively. Percentage cover of gorse was significantly higher (P<0.001) at 3.3 % in Grass Grass Grass treatments compared to all other treatments. PPP, FPP, TPP and TBP had 0.95, 0.7, 0.25 and 0.1 % gorse cover respectively. Greater numbers of gorse plants/m² were observed in GGG subplots compared to PPP and TPP subplots with 0 kg N/ha (low N). Under low N fertiliser treatment, GGG subplots had an average of 7 .2 plants/m² as opposed to PPP and TPP subplots that had 2.9 and 0.8 plants/m² respectively. Under high N fertiliser treatment, greater numbers of gorse plants/m² were also observed in GGG subplots with 6.6 plants/m² compared to 2.7 and 0.8 plants/m² for PPP and TPP subplots respectively. However, there was no significant effect of N fertiliser on gorse plant numbers/m² There was a significant effect of nitrogen fertiliser (P<0.05) on pasture production in all CS treatment plots in spring. Highest pasture mass was measured in FPP and PPP treatments at 1138 and 1013 kg DM/ha respectively, compared with TPP, TBP, GGG and FFP plots at 930, 930, 824 and 9 kg DM/ha respectively. High N fertiliser treatment (150 kg N/ha) increased triticale dry matter (kg DM/ha) in all cropping sequence treatments. In the absence of nitrogen fertiliser (low N treatment), linear relationships occurred between triticale dry matter (DM) production and increasing levels of specific soil properties. A corresponding (linear) increase between soil pH and triticale DM production was clearly evident, with the lowest DM yield occurring at pH 6.0 in PPP subplots and the highest DM yield occurring at pH 6.6 in FPP subplots. FPP cropping sequence plots produced the highest triticale dry matter yields and showed biologically optimum levels of pH and Ca for pasture growth. It is recommended that agriculturalists and land owners, under taking forest to pasture conversion, should incorporate some form of soil nutrient and pH level amelioration, via lime application, nitrogen fertiliser input and growing a of forage crop before final pasture establishment as a means of successfully controlling weeds and providing organic matter inputs. Establishment of legumes such as white clover and red clover in pasture following long-term forestry is an essential element for the success of conversion to a productive pasture-based livestock system.