The effect of intercropping on the yield and quality of forage oats and peas : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science at Massey University, Palmerston North, New Zealand

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Massey University
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Cereal-legume intercrops have the potential to improve dry matter yield and quality of forage. A study was conducted at Massey University in Palmerston North, New Zealand in 2020, to determine the effect of intercropping on the yield and quality of forage oats (Avena sativa L.) and peas (Pisum sativum L.). Oats and peas were sown in the oat: pea ratios; 100:0, 75:25, 50:50, 25:75 and 0:100. The sowing rates of 100% oats and peas were 150kg and 250kg ha⁻¹ respectively, from which seed rates for mixtures were calculated. Two harvests were taken, the boot (harvest 1) and milky dough stage (harvest 2) of oats and the dry matter yield and forage quality traits including crude protein (CP), Acid Detergent Fiber (ADF), Neutral Detergent Fiber (NDF) and metabolisable energy (ME) were determined. The sowing ratios significantly (P=0.05) affected the dry matter yield of forage at both harvests. At harvest 1, the sole cropped peas produced a significantly lower yield (5930 ha⁻¹) compared to the other treatments which were similar, producing yields that ranged from 14083kg ha⁻¹ to 15823kg ha⁻¹. At harvest 2, the 25% oat:75% pea treatment mixture had a significantly higher yield (21110kg ha⁻¹) than the sole cropped unfertilisedl oats (14353kg ha⁻¹), while the rest of the treatments were not significantly different from each other and produced yields ranging from 14885kg ha⁻¹ to 16690kg ha⁻¹. All forage quality parameters were significantly affected by sowing ratios at harvest 1 while at harvest 2 only the CP and NDF were significantly influenced by sowing ratios. At harvest 1, the CP content was significantly (P=0.05) higher in the sole cropped peas and mixtures compared to sole cropped oats and ranged from 13.24-17.45% while the ME was only significantly higher in the sole cropped peas. Sole cropped peas and mixtures also had significantly lower ADF and NDF levels compared to sole cropped oats. At harvest 2, only the 25% oat:75% pea mixture had significantly higher CP content (8.81%) content compared to sole cropped unfertilised oats (5.02%). Intercropping evaluation indices showed that all three mixtures had a yield advantage as mixtures produced land equivalent ratios of 1.06, 1.12, and 1.26 for the 50:50, 75:25, and 25:75 oat: pea ratios respectively. The plant height and leaf area index in this study were not significantly affected by sowing ratios at both harvests. Intercropping significantly improved the quality of forage harvested at the boot stage of oats, by increasing the CP and lowering the ADF and NDF content, improving palatability and digestibility of the forage. Land equivalent ratios of greater than 1 showed that intercropping produced greater yield per unit area compared to monoculture. Intercropping with peas can be used by farmers in the Manawatū area to improve the quality of oats grown for silage, the optimum seed ratio being 25% oat:75% peas.