INTRODUCTION Onion (Allium cepa) is the most important commercial vegetable crop produced in India for both domestic consumption and export. India accounts for 16% of the world’s area and occupies the second position after China in production with a share of around 14%. Karnataka contributes a major area in South India (84,800 ha) and produces 4,86,130 t of onion annually. Productivity, however, is much lower in India than the world average. In order to increase the production and quality, its nutrient requirements have to be carefully monitored through soil analysis for efficient fertilizer management programme. As no established standards are available, it was planned to develop soil nutrient standards for onion using diagnosis and recommendation integrated system (DRIS), which provides a means of simultaneously identifying imbalances, deficiencies and excesses in crop nutrients and ranking them in the order of importance (Beaufils, 1973). Beaufils and Sumner (1976) developed DRIS norms for P, K, Ca, and Mg to be applied to sugarcane culture on South African Diagnostic soil nutrient standards and identification of yield limiting nutrients in onion (Allium cepa) using DRIS K. Anjaneyulu Division of Soil Science & Agricultural Chemistry Indian Institute of Horticultural Research Hessaraghatta lake post, Bangalore-560 089, India E-mail: anjaney@iihr.ernet.in ABSTRACT Soil samples collected from a survey of fifty onion growing fields in Karnataka were analyzed for various macro and micronutrients for establishing a data bank to develop soil nutrient norms. By using Diagnosis and Recommendation Integrated System (DRIS), the whole population was divided into two sub-groups namely, low and high yielding and selected nutrient expressions that have shown higher variance and lower coefficient of variation as diagnostic norms, viz K/N (1.229), S/N (0.238), Ca/N (20.62), P/Zn (37.41), Mg/K (0.6.859), Fe/ Mg (0.004), Fe/Zn (5.736) etc. In addition, five nutrient ranges have been derived using mean and standard deviation as low, deficient, optimum, high and excess for each nutrient to serve as a guide for diagnostic purpose. The optimum organic carbon ranged from 7.1 to 11.0 g kg-l, N from 115 to 178 mg kg-l, P from 26 to 38 mg kg-l , K from 163 to 217 mg kg-l ,Ca from 2199 to 3398 mg kg-l , Mg from 802 to 1167 mg kg-l and S from 34 to 43 mg kg-l. Among DTPA extractable micronutrients, the optimum iron ranged from 3.40 to 4.34 mg kg-l, manganese from 5.84 to 6.66 mg kg-l, zinc from 0.67 to 1.01 mg kg-l and copper from 1.70 to 2.11 mg kg-l for onion. The diagnosis of nutrient imbalance identified through DRIS indices indicated that organic carbon, phosphorus and zinc were the most common yield limiting nutrients in onion. Key words: Nutrients, norms, DRIS indices, onion soils. Similarly, this methodology has been used to interpret the results of soil analysis for fruit crops such as mango and pomegranate (Raghupathi and Bhargava, 1997) in India. However, there are a few reports in the literature on the use of DRIS for developing soil nutrient standards for crops like onion. Therefore, an investigation was carried out to develop soil nutrient standards for onion using DRIS. MATERIAL AND METHODS A survey was conducted in major onion growing districts of Karnataka (Bellary and Chitradurga) and soil samples were collected from fifty fields during the year 2000-01. At each site, ten sub-samples were drawn and pooled. A composite sample was used for measurement of pH, EC, organic carbon, macro and micronutrients for developing nutrient standards. The samples were air dried, processed through 2 mm sieve and analyzed for different nutrients by using standard analytical methods (Jackson, 1973). Soil pH and EC were measured in 1:2.5 soil:water suspension. Organic carbon was estimated by wet J. Hortl. Sci. Vol. 3 (1): 39-42, 2008 page 39 40 oxidation method while P was analyzed colorimetrically after extracting in 0.5M NaHCO 3 (pH 8.5) solution. The exchangeable K, Ca and Mg were estimated after extracting in 1N neutral ammonium acetate. Micronutrients were analyzed after extracting in DTPA solution using atomic absorption spectrophotometer (Jackson, 1973). Thus, the data bank was established for the whole population. By using DRIS, the whole population was divided into two sub-groups namely low and high yielding (Beaufils, 1973) based on the yield performance of the fields. From the experience of the growers, 20 t/ha was considered as the cut off yield between low and high performing fields. The cut off yield was positioned in such a way that the high yielding sub-population reflects conditions that are deemed desirable (Beaufils, 1973). However, Letzsch and Sumner (1984) have shown that the actual cut off value used has little effect on the norms developed as long as it is not too low. Each parameter was expressed in as many forms as possible, e.g. N/P, P/N, NxP etc. Mean, variance and standard deviations were calculated for all forms of expressions together with the coefficient of variation. Among different forms of expressions, the one showing higher variance ratio (Variance of low yielding / variance of high yielding) was selected as norm (Walworth and Sumner, 1987). The DRIS indices were calculated by using the formula described elsewhere (Anjaneyulu, 2006). Five soil nutrient guides/ranges were derived using mean and standard deviation as deficient, low, optimum, high and excess for each nutrient. The optimum nutrient range is the value derived from “mean - 4/3SD (standard deviation) to mean + 4/3SD”. The range “low” was obtained by calculating “mean - 4/3 SD to mean - 8/3SD” and the value below “mean - 8/3 SD” was considered as deficient. The value from “mean + 4/3 SD to mean + 8/3 SD” was taken as high and the value above “mean + 8/3 SD” was taken as excessive (Bhargava and Chadha, 1993). RESULTS AND DISCUSSION Soil Nutrient concentration range The soil pH for the entire population (Table 1) ranged from 7.25 to 8.81, where onion is being grown successfully. The EC ranged from 0.12 to 0.54 dSm-1 and thus, the fields were in the safe range. However, the organic carbon level varied much between 3.3 to 16.8 g kg-l indicating that the content was low in many of the low yielding fields compared to the optimum value. The available P varied from 4.4 to 160.2 mg kg-l showing a wide variation among the fields. The exchangeable calcium and magnesium varied from 1658 to 4062 mg kg-l- and 453 to 1797 mg kg-1 respectively due to calcareous nature of the soil. Among the micronutrients, Fe ranged from 3.02 to 6.60 mg kg-1- and manganese from 3.30 to 37.50 mg kg-1- (Table- 1) indicating a wide variation in manganese compared to iron content. DRIS norms, indices and Nutritional Balance Index (NBI) A particular nutrient expression should have a high variance and low coefficient of variation to be chosen as norm for greater diagnostic precision (Walworth and Sumner, 1987). Among the nutrient expressions, certain diagnostic norms viz. K/N (1.229), S/N (0.238), Ca/N (20.62), P/Zn (37.41), Mg/K (0.6.859), Fe/Mg (0.004), Fe/ Zn (5.736) etc., have shown higher variance ratios compared to others and may have greater physiological rationale. In addition, maintaining the ratios of some expressions at the optimum when coefficient of variation was large was much less critical for the performance of the crop (Raghupathi et al. 2004). The nutrient imbalance in plants was diagnosed through DRIS indices that are given in Table 3 for selected low yielding orchards. As the value of each ratio function was added to one index sub-total and subtracted from another prior to averaging, all indices were balanced around zero. Thus, the nutrient indices sum to zero indicated an optimum level, negative values a relative deficiency and positive values a relative excess of that nutrient (Walworth and Sumner, 1987). The absolute sum values of the nutrient indices generate an additional index called nutritional balance index (NBI). The overall imbalance of the nutrient was assessed based on sum of the indices irrespective of sign (Table 3). Higher the sum value (2644), larger is the plant nutritional imbalance and, therefore, the lower will be the yield. However, the yield cannot be predicted from sum of the indices irrespective of the sign alone, because Table 1. Mean and S.D. of nutrients in the onion growing soils Soil Property Unit Mean S.D. pH - 8.36 0.2287 EC dSm-1 0.29 0.1391 OC g kg-l 11.0 0.2962 N mg kg-1 178.53 47.9996 P mg kg-1 38.88 9.9077 K mg kg-1 217.64 41.0786 Ca mg kg-1 3398.53 899.8555 Mg mg kg-1 1167.03 274.5240 S mg kg-1 43.46 7.3134 Fe mg kg-1 4.34 0.7575 Mn mg kg-1 6.66 0.6235 Zn mg kg-1 1.01 0.2645 Cu mg kg-1 2.61 0.8846 J. Hortl. Sci. Vol. 3 (1): 39-42, 2008 Anjaneyulu 41 of the influence of unmeasured factors that affect the yield (Sumner, 1977). The yield limiting nutrients were differing from field to field though some of the nutrients were more prominent. The order in which the nutrients were limiting the yield indicated that most often more than one nutrient was limiting the yield. However, the diagnosis of nutrient imbalance in the soils of onion growing tracts of Karnataka indicated that the most common yield limiting nutrients are organic carbon, nitrogen and phosphorus among the macronutrients and copper and zinc among the micronutrients. Optimum soil nutrients’ guide Nutrients guide/ranges have been derived using mean and standard deviation as deficient, low, optimum, high and excess for each nutrient and presented (Table 4). The optimum EC ranged from 0.11 to 0.29dSm-1 indicating a safe limit for the crop. All the low yielding gardens represented low organic carbon content compared to optimum, which ranged from 7.1 to 11.0 g kg-l in the soil. The optimum P ranged from 26 to 38 mg kg-1 and the low yielding fields were deficient in P as indicated by DRIS indices in table-3. Thus, majority of the soils representing low yielding fields were low in organic carbon and available phosphorus indicating their requirement. In onion the requirement of potassium is higher than nitrogen as it is involved not only in the production but also in improving the quality. Ninety per cent of the orchards surveyed were at optimum (163 to 217 mg kg-1) level for available potassium. Similarly, many fields recorded optimum to higher calcium, magnesium and sulphur contents in the soil indicating that these nutrients were not yield limiting in onion. Among the micronutrients, zinc and copper were found to be low in most of the low yielding fields followed by iron. The optimum zinc concentration ranged from 0.67 to 1.01 mg kg-1 whereas copper ranged from 1.70 to 2.61mg kg-1. However, 87% of the fields recorded optimum levels of manganese indicating that manganese is not a yield- limiting factor. Thus, the possibility of making a successful diagnosis based on soil nutritional status increases as the Table 2. DRIS ratio norms for onion growing soils Selected Ratios Norms CV% Selected Ratios Norms CV% P/N 0.202 46 Cu/K 0.016 48 K/N 1.229 22 Mg/Ca 0.336 30 Ca/N 20.62 29 S/Ca 0.014 68 Mg/N 7.087 35 Fe/Ca 0.001 25 S/N 0.237 30 Mn/Ca 0.002 63 Fe/N 0.026 30 Ca/Zn 4673 52 Mn/N 0.041 70 Cu/Ca 0.001 33 N/Zn 233.6 42 Mg/S 37.45 52 Cu/N 0.016 52 Fe/Mg 0.004 29 K/P 10.45 68 Mn/Mg 0.006 50 Ca/P 189.1 67 Mg/Zn 1626 71 Mg/P 74.69 63 Cu/Mg 0.002 38 S/P 1.869 51 Fe/S 0.139 64 Fe/P 0.232 62 Mn/S 0.208 70 Mn/P 0.491 64 S/Zn 55.66 64 P/Zn 37.41 27 Cu/S 0.094 61 Cu/P 0.157 63 Mn/Fe 1.455 67 Ca/K 20.91 43 Fe/Zn 5.736 25 Mg/K 6.859 30 Cu/Fe 0.598 32 S/K 0.223 52 Mn/Zn 8.556 70 Fe/K 0.025 33 Mn/Cu 2.456 52 Mn/K 0.037 40 Cu/Zn 3.592 56 K/Zn 274.1 43 — — — Table 3. DRIS Indices for selected Onion growing fields F.No pH EC OC N P K Ca Mg S Fe Mn Cu Zn NBI(Sum) 1 52 5 -90 15 -66 31 25 14 74 -6 103 -75 -82 638 2 -1 99 -160 -175 -137 163 204 68 28 46 58 -53 -140 1332 3 150 36 -26 34 -2 -127 206 204 105 -146 111 -241 -304 1692 4 106 28 -101 21 -128 26 104 50 65 41 152 -29 -335 1186 5 62 52 -153 41 -111 -113 195 135 90 -2 26 -2 -220 1202 6 107 -143 -267 203 -347 -347 216 114 262 108 169 143 -218 2644 J. Hortl. Sci. Vol. 3 (1): 39-42, 2008 DRIS norms for onion 42 number of nutrient-related yield limiting factors that are due to nutrition is increased. As with foliar diagnosis, the use of DRIS with soil data also provides the advantage of taking into account nutrient balance and ranking nutrients in terms of abundance relative to optimal levels. REFERENCES Anjaneyulu, K. 2006. Development of diagnostic leaf nutrient norms and identification of yield limiting nutrients using DRIS in rose grown under protected conditions. J. Hortl. Sci. 1: 28-32 Bailey, J. S., Beattie, J. A. M. and Kilpatrick, D. J. 1997. The diagnosis and recommendation integrated system (DRIS) for diagnosis of nutrient status of grassland swords.1 Model establishment. Pl. and Soil, 197: 127-135 Beaufils, E. R. 1973. Diagnosis and recommendation integrated system (DRIS). Soil Science Bulletin,1: 1-132. University of Natal Pitermariburg, South Africa Beaufils and Sumner. 1976. Application of the DRIS approach for calibrating soil, plant yield and plant quality factors of sugarcane. Proc. S. Afr. Sugar Tech. Assoc., 50: 118-124 Bhargava, B. S. and Chadha, K. L. 1993. Leaf nutrient guides for fruit crops. In: Advances in Horticulture- Fruit Crops, Vol. 2:973-1030, Chadha, K. L. and Pareek, O. P. (Eds), Malhotra Pub. House, New Delhi. Jackson, M. L. 1973. Soil Chemical Analysis, Prentice Hall of India, New Delhi. p 498 Letzsch, W.S. and Sumner, M. E. 1984. Effect of population size and yield level in selection of DRIS norms. Comm. Soil Sci. Pl. Anal. 15:997-1006 Mourao Filho, F. A. A. 2004. DRIS: Concepts and Applications on nutritional diagnosis in fruit crops, Sci. Agric., (Piracicaba, Braz.), 61: 550- 560 Raghupathi, H. B. and Bhargava, B. S. 1997. Preliminary soil fertility norms for Ratnagiri Alphonso mango. J. Ind. Soc. Soil Sci., 45: 534-536 Raghupathi, H. B., Reddy,Y. T. N., Kurian Reju and Bhargava, B. S. 2004. Diagnosis of nutrient imbalance in mango by DRIS and PCA approaches. J. Pl. Nutr. 27:1131-1148 Sumner, M. E. 1977. Application of Beaufils diagnostic indices to corn data published in literature irrespective of age and condition. Pl. and Soil, 46: 359-363 Walworth, J. L. and Sumner, M. F. 1987. The diagnosis and recommendation integrated system. Adv. Soil Sci., 6:149-188 (MS Received 11 October 2007, Revised 10 January 2008) Table 4. Soil nutrient standards for onion Nutrient Unit Deficient Low Optimum High Excess Org. Carbon g kg-l <3.1 3.1-7.0 7.1-11.0 11.1-15.0 >15.1 Nitrogen mg kg-l <50 51-114 115-178 179 -242 >243 Phosphorous mg kg-l <12 13-25 26-38 39 -52 >53 Potassium mg kg-l <108 109-162 163-217 218-272 >273 Calcium mg kg-l <998 999-2198 2199-3398 3399-4598 >4599 Magnesium mg kg-l <434 435-801 802-1167 1168-1533 >1534 Sulphur mg kg-l <23 24-33 34-43 44 -53 >54 Iron mg kg-l <2.32 2.32-3.33 3.40-4.34 4.35-5.35 >5.36 Manganese mg kg-l <5.00 5.00-5.83 5.84-6.66 6.67-7.49 >7.50 Zinc mg kg-l <0.31 0.31-0.66 0.67-1.01 1.02-1.36 >1.37 Copper mg kg-l <0.77 0.77-1.69 1.70-2.61 2.62-3.52 >3.53 J. Hortl. Sci. Vol. 3 (1): 39-42, 2008 Anjaneyulu