The effects of nitrogen on ryegrass seed production

Pasture plants, particularly the perennial species, are poor seed producers. Where the seed itself is agriculturally important, as in cereals, excessive vegetation is unnecessary for maximum yields per acre and a real disadvantage for effective harvesting. With pasture plants the continued production of herbage is essential for animal fodder and is also a means of maintaining the productivity of the sward for some years. Prolific seed production can therefore be an inherent disadvantage. Selection for herbage production has normally resulted in selection against seed production. Multi-tillering, as in the genus Lolium, ensures leafiness and good production, especially under conditions of high fertility and intensive management. However the seed potential is generally low because of the low proportion of tillers which have the ability to develop inflorescences each year (Lambert, 1967a; Robson, 1968). Two methods are available for increasing seed productivity in grasses: (1) selection for increased yield and (2) management of the seed stand for increased yield. It is the second method which has received most attention. Management practices encourage flowering and seed production include the use of low plant densities, irrigation, controlled grazing and heavy nitrogen applications. These are basically principles of crop production and therefore a grass grown for seed must be managed as a crop if maximum seed yields are to be obtained. In New Zealand and particularly in Canterbury, there is great potential for high grass seed yields. However seed producers do not grow specialist seed crops, and the amount of seed produced per acre each year is primarily dependent on the stock feed situation in spring. In Canterbury low seed yields obtained over a number of seasons are not only the result of the poor integration of livestock management with seed crop management but also because of the present lack of firm crop management recommendations available to seed producers, particularly with respect to nitrogen fertiliser applications. More detailed knowledge of the development of the plant and the use of this knowledge in the controlled management of the crop throughout the year would be a precise and predictable method of obtaining consistently high seed yields. The present study was therefore designed to obtain information, under New Zealand conditions, on the effect of relating applications of nitrogen fertiliser to two distinctive stages of reproductive development of New Zealand Grassland's Ruanui perennial ryegrass (Lolium perenne L.) grown as a specialist crop for the production of seed. A similar study involving single plants of New Zealand Grassland's Manawa short-rotation ryegrass (L. perenne x L. multiflorum) was conducted under controlled environment conditions. The above two species are collectively the most important of the pasture grasses in New Zealand (New Zealand Official Yearbook, 1969)