Role of mixed herb leys in New Zealand organic cropping systems : a dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours) in the Lincoln University [i.e. College]

Abstract

Above ground dry matter production, sward composition, and herbage mineral levels were measured from three ley mixtures sown on a Wakanui silt loam, Lincoln College, Canterbury. Additionally soil fertility (exchangeable sodium, potassium, calcium and magnesium, total nitrogen, total carbon, and phosphorous fractions) and aggregate stability were measured from the three ley treatments and a continuously cropped site.

The three treatments were a ryegrass (Lolium perenne) white clover ley (Trifolium repens) ley, a lucerne (Medicago sativa) - grass based mixed herb ley, and a lucerne based mixed herb ley.The continuously cropped site was newly sown in tall fescue (Fesiuca arundinacea) for seed. Previous crops were broad beans (Vicia faba), linseed (Linum usitatissimum), wheat (Triticum aestivum), ryegrass, and white clover.

Literature reviewed suggested poor herb survival in mixed herb leys in the presence of legumes and grasses, and insignificant differences in the mineral status of the surface soil. Results showed herb percentage of total dry matter was low (<10%). Differences in soil fertility between ley treatments were small, but significantly greater (P < 0.05) than the continuously cropped site. Aggregate stability was low (20%) in the continuously cropped site, and increased to 48% with increasing grass percent in the ley treatments. Chemical analysis of herbage showed chicory (Cicorum intybus) was highest in phosphorous and zinc but it was not consistently higher in all minerals compared to other species as, reported by other studies.

It is concluded that deep rooting perennial herbs such as chicory have no advantage over deep rooting, nitrogen fixing legumes such as lucerne.