Browsing by Author "Chandrasiri, Nipuni Kaushyali"

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Comparing nutrient leaching between standard and diverse pasture under sheep grazing : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science, School of Agriculture and Environment, Massey University, Palmerston North, New Zealand
(Massey University, 2024) Chandrasiri, Nipuni Kaushyali
Current intensive sheep farming in New Zealand has led farmers to focus on improving economic outcomes based on production. Thus, in such an environment, there is a potential risk to contaminate soil and waterways with nutrients, more specifically as nitrate. However, there is lack of knowledge on nitrate leaching in modern sheep farming systems, particularly in the context of using perennial diverse pasture mixes coupled with regenerative pasture management practices. The objective of this study was to compare the nitrate leaching concentrations and quantify nutrient losses in both diverse pasture and standard pasture systems under regenerative pasture management and contemporary pasture management over one year from January to December 2023. This study was conducted on a poorly-drained, fine-textured Tokomaru silt loam soil at Massey University’s Whenua Haumanu sheep farmlet study located at the Pasture Crop Research Unit, near Palmerston North, Manawatū, New Zealand. The study design was a randomised complete block design containing eight drainage paddocks (each approximately 0.25 ha) including two pasture types (standard and diverse) and two management practices (contemporary and regenerative) each with two replicates. Each paddock had an independent mole-pipe drainage system. Standard pasture treatments were sown with perennial ryegrass (Lolium perenne), white clover (Trifolium repens) and red clover (Trifolium pratense) and diverse pasture treatments were sown with a mix of 21 species which resulted in six dominant species including perennial ryegrass, cocksfoot (Dactylis glomerata), white clover, red clover, plantain (Plantago lanceolata) and chicory (Cichorium intybus). Regenerative pasture management treatments were managed with longer grazing intervals, higher post-grazing residuals and low to no mineral fertiliser and chemical use while contemporary pasture management treatments followed the Beef and Lamb New Zealand best practice grazing advice for sheep and used mineral fertiliser and chemicals as required. The drainage volume and concentrations of nitrate N, nitrite-N, ammonium-N and dissolved reactive phosphorus (DRP) in each drainage paddock were measured to estimate the nutrient loads. In addition, pasture growth rate and accumulated dry matter mass were monitored along with botanical composition. Due to improper functioning of one of the drainage pipes, the data from one replicate was not usable, so the data were analysed by comparing pasture types and ignored the effect of management type. The measured total cumulative drainage (mm) was higher (p<0.05) in diverse pasture treatment than the standard pasture treatment. The total loads of nitrate (kg N/ha) were higher (p>0.05) in standard pasture treatments (1.04 kg N/ha) than in diverse pasture treatments (0.73 kg N/ha). The diverse pasture treatment had visually greater pasture growth and accumulated dry matter yield, and greater herb contents than the standard pasture treatments which likely caused the numerically lower nitrate concentrations observed in the diverse pasture treatments than the standard pasture treatments. Overall, the measured loads of nitrate-N, nitrite-N ammonium-N and DRP in both treatments were very small (<1.0 kg /ha). These low loads in contaminants were likely because all the drainage paddocks were not grazed until late autumn as they were cut for hay and then allowed to recover early in the year. Therefore, the amount of urinary N loading that occurred during late summer, early autumn would have been minimal. Overall, diverse pastures have the potential to reduce nitrate leaching in sheep grazing systems.