Nitrogen in agriculture as affected by the kind of fertilizer. II. Nitrogen in soil and plant

Since nitrogen is a main nutrient of plants thus representing a limiting factor to yield, an analytical method should be contrived to determine the adequate amount of fertilizer to be added to optimize production without harming the environment. A plot-trial was established on an existing farming-site located near Vienna in an area called ,,Obere Lobau" to compare variants treated with compost, mineral-fertilizer and controls. Different forms of nitrogen in soil and plants (i.e. rye) were investigated. Samples were taken from 21/05/1997 to 02/07/1997 about every two weeks. The N-min-method is of little avail when organic manure is concerned due to the quick uptake of nitrate by the plants and the slow mineralization rate of the manure. An analytical method to estimate SRNH (soil-nitrogen soluble in hot dinatriumhydrogenphosphatebuffer) was established, which is believed to represent the potential amount of nitrogen available during the vegetation period. The investigations proved this farming-site to be well supplied with nitrogen, which entailed a luxurious consumption of nitrogen by the plants, especially in the plots with mineral fertilization. Compost showed a slow and longterm mineralization rate thus enabling the uptake of nitrogen according to need only in contrast to ,,force feeding" in conventional systems. Compost-manuring resulted in a higher content of total nitrogen and SRNH in the soil.