PREDICTING THE BEST TIME TO APPLY NITROGEN TO GRASSLAND IN SPRING

A great number of experiments with varying dates of N application to grassland showed that the most suitable time of applying spring N in tbe Netberlaods varies, as a result of weather conditions, from year to year from mid-February to mid-April. In such experiments the best time of spring N application, which needs to be known in advance, can only be determined after the grass bas been harvested and weighed. The results of these experiments supported the opinion that the best application date coincides with the banging of grass growth. However, at that time it was not possible clearly to define the begimiing of grass growth. When in 1959 a measuring disc was put into use the beginning of grass growth could be precisely determined and it was then found that the beginning of grass growth was closely correlated to a certain accumulated temperature from 1 Jan. from which the date of the beginning of grass growth can be predicted. This date is the most suitable one for applying spring N to grassland.     

THE EFFECTS OF SHOOT REMOVAL ON THE RHIZOME CARBOHYDRATE RESERVES OF COUCH GRASS (AGROPYRON REPENS (L.) BEAUV.)

Summary. Three box experiments examining the effects of shoot removal on rhizome carbohydrate reserves are reported.
During summer in England the optimum frequency of hand defoliation for maximum loss of carbohydrate was 10–14 days. As in previous experiments, high levels of soil nitrogen sometimes increased the rate of carbohydrate loss from 9-in. rhizome pieces. This result was obtained when nitrogen was supplied as a nitrate, an ammonium salt, or urea.
Repeated applications of 2 or 4 oz/ac paraquat over a period of about 60 days reduced carbohydrate reserves to about 50% of the level obtained with the same number of hand clippings. It is suggested that paraquat may have been translocated to the rhizomes, the carbohydrate content of which may have been reduced by an effect of the paraquat on the respiration rate.
When plants which had been subjected to different methods and frequencies of defoliation were uprooted and buried beneath 2 in. of soil, there was a connection between the rhizome carbohydrate content at the time of burial, the ability of the plants to regenerate, and the rate at which new carbohydrate reserves built up during the following two months.