Application of DRIS to white clover based pastures

Abstract

There are basically two approaches for interpreting chemical analysis of plant tissue to assess nutrient status and fertilizer need. The oldest, called the critical value method (CVM), is based on nutrient concentrations in the sample compared with levels required for near maximum growth. The other is based on the ratios of nutrient concentrations. The Diagnosis and Recommendation Integrated System (DRIS) is a system that uses nutrient ratios, comparing these with “norms”; which are ideal ratios derived from high yielding plants. DRIS integrates the ratios to give an index for each nutrient considered and ranks them in the order of deficiencies. It is helpful in dealing with multiple deficiencies. The DRIS system has not previously been tested on white clover (Trifolium repens L.)‐based pasture in New Zealand. The purpose of this study was to develop N, S, P, K, and Ca DRIS norms for white clover; to use these norms in computing DRIS indices for clover samples from fertilizer trials; to compare the diagnosis of the S and P status of clover samples with CVM and DRIS; and to compare deficiency rankings of S and P by DRIS with DM responses to S and P fertilization. Norms for high country and lowlands were based on mean clover nutrient contents in high yielding plots in field trials, using plots which gave >90% of maximum yield (95 out of 996 high country samples and 338 out of 1597 lowland samples). The lowland norms of N, S, P, and K concentrations ranged from 18 to 32% higher than concentration norms for high country, whereas differences in the ratios of these elements varied from only three to nine percent, The Ca concentrations were similar for high country and lowlands. Critical nutrient concentrations selected to give best differentiation between deficiency and adequacy of S and P were twice as great in the lowland trial as in the high country trial. This problem of variable criteria was greatly reduced by the use of DRIS when indices were calculated from N, S, and P ratios only. With either set of norms the critical index values separating deficient and adequate samples were close to zero for both S and P. Including more variables such as K and nutrient concentrations in the DRIS equations gave a wider spread in critical index values thus making the diagnosis more restricted to conditions from which norms were derived. It was concluded that the adoption of DRIS as an aid in interpreting white clover plant analysis data would be helpful, especially in ranking S and P deficiencies, and in making recommendations for applying S and P in proportions best related to plant needs.