EFFECT OF TIME OF SAMPLING ON THE DIAGNOSIS OF THE N, P, K, Ca, AND Mg REQUIREMENTS OF SUGARCANE BY THE DRIS APPROACH

A 3, NPK lime factorial experiment is used as a means of testing both soil and leaf norms for sugarcane obtained by the Diagnosis and Recommendation Integrated System (DRIS) developed by Beaufils. ,Soil and leaf samples were taken from the experiment when the cane was 3, 6, 12 and 18 months old respectively and analysed for a number of essential plant nutrients. The results show that these norms can be validly used in making diagnosis of the N, P, K, Ca and Mg requirements of sugarcane at the four sampling times. Diagnoses by the DRIS approach have the advantage over the threshold value approach in that they can be made over a wide range of ages of material sampled. This is clearly brought out by a comparison of the successes of the two diagnostic techniques. The importance of balance in plant nutrition is emphasized and illustrated by an example on cane lodging. To study balance it is essential to take both soil and plant composition into account simultaneously. Introduction One of the main advantages of the Diagnosis and Recommendation Integrated System (DR1S)lf ' 9 3 9 4 9 5 9 6 for making fertilizer and other treatment recommendations is its ability to make diagnoses irrespective of stage of plant growth and environmental conditions. Past results have indicated that this is likely to be as true for sugarcane7? **l1?l4 as it has been found for other crops1? 2~ 3 9 4 9 15> 17. The object of this paper is to test and illustrate this point using both leaf and soil data for sugarcane derived from an NPK lime factorial experiment which showed yield responses to the factors studied. Experimental procedures The provisional norms for leaf and soil parameters against which the data from the experiment are compared have been presented previously together with details of the manner in which the DRIS indices are calculated7? The experiment used for this purpose was a single replication of a 3, NPK lime factorial laid down on Cartref soil series at the Huletts Estate at Darnall. The experiment was fertilized on 23/11/74 and planted on 30/11/1974 using the variety NCo 376. The treatment levels are presented in Table 1. TABLE 1 Levels of nutrients applied in factorial experiment The reason for using such high levels of fertilizer was not to attempt to reach maximum yields but rather to induce imbalances in both soil and plant in order to obtain a better understanding of the relationship between fertilizer applied, its reaction with the soil and the resultant influence on the plant. Nutrient N as urea (kg/ha) . . . . . P as single supers (kg/ha) . . . K as KC1 (kg/ha) . . . L as dolomitic lime (mton/ha) . Both soil (Mount Edgecombe auger) and leaf (3rd leaf blade) were sampled on each plot four times during the growth of the plant crop. Samples were taken on 28/2/1975 (3 month old cane), 6/6/1975 (6 month old cane), 5/12/1975 (12 month old cane) and 28/6/1976 (18 month old cane). At harvesting on 3/7/1976 yield and sucrose content were recorded. Because the sucrose content did not vary much (13-14%) over all the plots in the experiment only tons cane per hectare has been used as a yield parameter. Before the start of the experiment the soil representative of the experimental area had the following composition: