Assessment of nitrogen status of soils with respect to the growth of cereal crops
The literature on the assessment of nitrogen status of soils by soil and plant analysis is critically reviewed. Two field experiments over two field seasons in two locations were utilized to evaluate selected soil and plant tests of N status. A range of N supply conditions was studied. The test crop was barley in both years. The inorganic N level in the soil and the nitrogen and pigment concentrations and dry matter yield of the plants were monitored at selected dates during the growing season. Profile inorganic N assessment was affirmed as a method of predictive potential, with sampling below 13 cm advisable for predictive purposes. Plant N concentration during vegetative growth was significantly related to end-of-season parameters. Concentrations of chlorophyll (a, b and a + b) and carotenoids were significantly related to N concentration and N treatment. N treatment was shown to significantly affect the ratio of green to yellow pigments but it was not confirmed that N supply significantly affected the ratio of chlorophyll a: chlorophyll b. Absolute pigment concentrations were more significantly related to N supply than pigment ratios. Plant chlorophyll concentration and plant N concentration were similarly related to parameters reflecting the overall seasonal supply of H. Rates of dry matter production and N offtake were calculated and expressed relative to rates achieved in conditions of non-limiting N supply. These were shown to be related to end-of-season parameters. The practical significance of and the limitations to the conclusions drawn are discussed.