Comparative evaluation of DRIS (Diagnosis and Recommendation Integrated System) and CNL (Critical Nutrient Level) approaches for nutrient deficiency diagnosis in sugarcane

Abstract

Sugarcane crop and sugar industry play pivotal role in the economy. Imbalanced nutrition limits the crop yield. Sugarcane nutrition tools based on soil test and tissue nutrient concentrations using traditional Critical Nutrient Levels (CNL) approach has limited applicability. Plant nutritional status interpretation, based on comparison of nutrient pairs with norms developed for higher yielding populations known as Diagnosis and Recommendation Integrated System (DRIS) could prove better for diagnosis of nutrient imbalances and optimizing sugarcane nutrition. One hundred twenty three observations on macro- and micronutrient concentration and associated yield with known soil type and sugarcane varieties were recorded through a field survey and DRIS norms were developed for sugarcane in lower Sindh (district Thatta). Third leaf and sheath (and fourth leaf for comparison) was sampled at the grand growth stage during mornings (7:00 am to 10:30 am) from each of the 123 sugarcane plantations. The plant samples were oven dried at 68 °C, ground, and digested in HNO3:HClO4 acids mixture (5:1). The digests were analyzed for phosphorus colorimetrically, potassium, copper, iron, manganese and zinc through atomic absorption spectroscopy, and nitrogen was measured by Kjeldahl’s method; and plant boron was determined through dry ashing and the concentration was measured colorimetrically. Surface soil samples were collected from each of the 123 sites, air dried and crushed to pass through 2mm sieve, and analyzed for EC, pH, calcium carbonate, particle size distribution, nitrate nitrogen, plant available phosphorus, potassium, zinc, copper, iron, boron and manganese. Nitrate was extracted in 2 M KCl and measured colorimetrically. Plant available phosphorus zinc, copper, iron, and manganese were extracted by ABDTPA, and boron with hot boiling water. The plant nutrient concentration data was fitted to DRIS using Beaufils methodology. Yield was recorded by harvesting 5x3 m2 area by each location. The data were organized on soil association and variety basis for each location, and analyzed for variance using general linear model implemented through SAS version 9.2. The soils were calcareous with pH 7.7 to 8.7 (mean 8.2), low in soil test nitrogen, low to medium in extractable P, and adequate in extractable potassium. Among the micronutrients, zinc was low, boron was medium and copper and iron were adequate. The soil test level differed a little with soil association except for plant available iron. Selected soil nutrients were found spatially variable. The soil zinc was lower in Mirpur Sakro and Thatta sub districts (Talukas) and high soil zinc was towards Sujawal-Jati sub districts. Similar spatial pattern existed for plant available iron, potassium, and boron which was related with soil type; and the land capability map further helped to understand the spatial variation in the nutrient status in the sugarcane growing area. Plant index tissue nutrients differed significantly (p < 0.01) with the soil type except for nitrogen and phosphorus. The highest accumulation of potassium in plant was from Borium, Gungro, and Arib soils and lowest from Gujo and Katiar soils. The highest copper concentration was observed in sugarcane grown on Gujo soil association while the lowest copper concentration was found in sugarcane grown on Bulri soil associations. Plant nutrient concentration also differed significantly with variety. The sugarcane varieties BL-4, Thatta-10 and Triton had nitrogen and phosphorus contents below their critical value and out of the optimum range. Potassium was above the critical value, even greater than the optimum range. Zinc was in the optimum range in sugarcane grown on Gujo, Gujo-Shahdara complex, Daro, and Rustam, and below the optimum range in other soils. Boron was lower than the optimum range on Borium and Bulri soils. Copper was optimum on all the soils and iron was deficient on all the soils. This suggested that edaphic factors influenced nutrient levels in plant. Also, Triton which normally had greater nitrogen content than BL-4, had lower N content when grown on Arib soil. Overall, N and K nutrients in Triton were below the critical value and optimum range. BL-4 grown on Daro soil had more N than the sugarcane varieties Triton and Thatta-10. In Gungro soil, BL-4 had lesser N than Thatta-10 and Triton. Similar is the case in Rustam soil. Therefore some varieties were better accumulator of some micronutrients on certain soils than the other varieties grown on the same soil. The mean and range of individual nutrients were different in low and high yielding populations of the varieties. High yielding population had greater nitrogen, phosphorus, potassium and manganese than the low yielding population of respective varieties. The magnitude of difference for zinc and boron was far greater while copper and iron concentration difference between low and high yielding populations was negligible. Low yielding population had wider nitrogen phosphorus ratio than high yielding population of corresponding varieties, while nitrogen to potassium ratio had opposite trend. Similarly the ratio of nitrogen to micronutrients was wider in low yielding population suggesting more nitrogen than micronutrients. The contrasts for the nutrient ratios between low and high yielding populations are discussed. DRIS indices derived from sugarcane fields of lower Sindh revealed that nitrogen ranged from 2.96 to 4.51which indicated that nitrogen was sufficient under the current practice of fertilization. The phosphorus index value of -6.23 to 3.58 indicated deficiency and the need for additional phosphorus application was identified for certain varieties. The potassium indices of 2.57 to 8.10 indicated high level of potassium in the sugarcane plant tissue. This level of potassium as determined by the DRIS reflected the luxurious uptake of potassium by the sugarcane. The indices for zinc ranging from -12.23 to -8.92, magnitude of difference from zero of balanced nutrition showed the severity of deficiency. From the results and comparison with other studies it was apparent that the potential response of sugarcane is likely to be high to the application of zinc. The indices for boron ranged from -14.87 (deficient) to -0.26 (adequate) showing the most severe deficiency of this element indicating high probability of response to boron application. The average indices of copper ranged from 4.59 to16.17 and iron from 7.24 to 12.98, indicating high status of these nutrients in the sugarcane plant tissue. The study provides guidelines for sugarcane nutrition on a regional level, large commercial growers and policy makers can benefit from the findings.