ABSTRACT
In annual pastures utilized for grazing, the amount and quality of the standing dry matter in the dry season is of importance for the performance of the animals. Often both characteristics decline at the end of the green season. It is shown, that dispersal of the reproductive structures of the vegetation may be the main reason for this phenomenon. Determination of the reproductive effort of the annuals indicates that the proportion of their total production invested in reproductive tissue may be as high as that of cultivated species. It is shown that the harvest index (or seed ratio) of annual species is closely related to nutrient (mainly nitrogen) transfer from vegetative organs to the reproductive organs in the period between flowering and maturity, when in most cases, additional uptake of nitrogen from the soil is negligible. The effect of environmental and genetic effects on these processes is discussed.
ABSTRACT
A model is presented that simulates nitrogen uptake and response to nitrogen deficiency by a growing annual plant canopy. It is a descriptive model as it is not based on a detailed definition of the biochemical processes involved. It does incorporate a considerable amount of experimental knowledge about these processes as well as some tentative concepts concerning the availability of soil nitrate and the relation between rates of growth, death and nitrogen translocation to the seeds. The model simulates the effect of nitrogen deficiency on plant growth, seed development, death of vegetative tissues and changes in the nitrogen concentration of the different plant parts. The results warrant a verification and development study under specific field conditions. The model is meant to be used in conjunction with another model that simulates the water balance and transpiration of an annual plant canopy under moisture limiting conditions. The nitrogen balance in the soil is not yet treated in either model.
ABSTRACT
A model is presented that simulates nitrogen uptake and response to nitrogen deficiency by a growing annual plant canopy. It is a descriptive model as it is not based on a detailed definition of the biochemical processes involved. It does incorporate a considerable amount of experimental knowledge about these processes as well as some tentative concepts concerning the availability of soil nitrate and the relation between rates of growth, death and nitrogen translocation to the seeds. The model simulates the effect of nitrogen deficiency on plant growth, seed development, death of vegetative tissues and changes in the nitrogen concentration of the different plant parts. The results warrant a verification and development study under specific field conditions. The model is meant to be used in conjunction with another model that simulates the water balance and transpiration of an annual plant canopy under moisture limiting conditions. The nitrogen balance in the soil is not yet treated in either model.