Some aspects of the competition between seedlings of gorse (Ulex europaeus L.) and "Grasslands Nui" perennial ryegrass (Lolium perenne L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
Two glasshouse trials were conducted with "Grasslands Nui" perennial ryegrass (Lolium perenne L.) and gorse (Ulex europaeus L.) grown in boxes separately as monocultures and as mixtures forming a replacement series. The first trial was continued for 22 weeks after sowing to assess the effects of defoliation at 2 and 4 cm in comparison with controls. Defoliated treatments were cut 14, l8 and 22 weeks after sowing and the harvested dry matter weighed. In the second trial, the response of the two species to eight fertilizer treatments (nil, N, P, K, NP, NK, PK and NPK) was assessed 18 weeks after sowing. In trial one, Nui grew faster than gorse and produced more dry matter over all harvest periods. The proportion of gorse in mixtures increased with repeated cutting, while the Nui decreased. Over all harvest periods, gorse growth was depressed in mixtures with Nui and even with the smallest proportion of ryegrass (1 Nui to 3 gorse), total weights of gorse shoots were reduced by about 75%. The total root and whole plant dry weights followed a similar pattern as did the numbers of root nodules. The ratios of shoot:root weights were higher in mixtures than in monoculture. With gorse, between the first and second cuts the low cut treatment outyielded the high cut but with subsequent cuts the low cut plants made less growth. Total shoot, root, and whole plant weights and root nodule numbers were depressed by both defoliation treatments in comparison with the uncut controls and the depression was greater with the lower than the higher cutting level. The shoot:root ratio and side shoot numbers were higher in the defoliated than in the undefoliated treatments. The total growth of Nui was not significantly reduced when grown in mixtures at ratios of 1 gorse to 3 Nui or equal numbers of each. At the 1 Nui to 3 gorse ratio, however, Nui growth was reduced by almost 20%, The shoot:root ratios and number of tillers per box were higher in monocultures than in mixtures. Cutting reduced the final dry weights of Nui. The number of tillers was also decreased while the shoot:root ratio was increased. The effects of the second and third cuts were greater than those of the first cut but there was no significant difference between the two cutting heights. Analysis based on de Wit's competition model showed that Nui was more competitive than gorse for most of the yield components measured and suggested that in most cases the two species were competing for different space. Gorse was at a competitive disadvantage when grown in association with Nui, both in the defoliated and undefoliated treatments. Increasing the proportion of ryegrass in mixtures severely restricted the growth of gorse seedlings. The high growth rate of Nui led to suppression of gorse by shading and the effect was accentuated by defoliation. In the second trial, gorse produced a greater dry weight of shoots than roots while with Nui a greater weight of root was produced than shoot. As in the first trial, the grass made considerably more growth than the gorse. In the mixtures which contained 75% gorse and 25% Nui plants, the dry matter production of gorse shoots + roots was only 16% of the total of the two species. Nodule production per plant was reduced by about half. Gorse dry weight,nodule numbers and shoot:root ratios were higher with all treatments containing P than in the controls or boxes treated with N, K or NK. Fertilizer treatments did not affect the proportion of gorse shoots in the mixtures but there was a reduction in the roots with P treatments. With the grass also, all P-treated boxes yielded more shoot and root dry weights and tillers than the control or N and K treatments. The total plant dry weight was higher than the control with a1l fertilizers except K. In contrast with gorse addition of P fertilizers reduced the shoot:root ratio. The use of fertilizers and defoliation in relation to the control of gorse seedlings in the field has been discussed.