Evaluating the Nutritional Status of Lisbon Lemon and Perl Tangerine gardens in Dezful Using DRIS and DOP Methods

Citrus is an important fruit crop in Iran. One of the main reasons for decreasing yield of these plants, in addition to moisture stress, is their unbalanced nutrition, so nutrient balance is an important factor in increasing quantity and quality of crop production. In proper plant nutrition, each nutrient must not only be sufficiently available to the plant but also create a state of equilibrium, and observance of the ratio between the nutrients is of particular importance. Diagnosis and recommendation integrated system (DRIS), and deviation from optimum percentage (DOP) can be used as efficient methods to interpret the results of plant analysis and the nutritional diagnosis in crops and fruit trees. In the north of Khuzestan, due to the dense cultivation of trees and soil depletion of the plant's nutrients, it requires widespread use of fertilizers containing macro and micronutrients. The objective of this study was to determine the optimum level of the nutrients and evaluate the nutritional status of Lisbon lemon (Citrus lemon) and Perl tangerine (Citrus tangerina) in Dezful area using DRIS and DOP methods. 30 Lisbon lemon and 30 Perl tangerine gardens were randomly selected from citrus gardens in Dezful region in the south of Iran. Leaf samples as composite were collected from non-fruiting branches in late September 2015, and N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, and B concentrations were determined. DRIS norms were achieved from the gardens with high-yielding. Then, DRIS and DOP indices for nutrients in the gardens with low-yielding, considering average yield, were calculated to evaluate nutrients balances and order of nutrient requirements. Sufficiency ranges of macro and micronutrients were derived by the DRIS method. The mean concentrations of nutrients in the high-yielding population were used as reference values to calculate DOP indices. Finally, nutritional balance index (NBI) was calculated for all nutrients. The results showed that the optimum level of the nutrients in Lisbon lemon leaves were 2.97, 0.11, 1.85, 3.88 and 0.17% for N, P, K, Ca, Mg, and 200.5, 24.9, 23.9, 68.8, 32.9 mg kg-1 for Fe, Zn, Mn, Cu, and B, respectively. Also, the optimum level of these nutrients in Perl tangerine leaves were 2.97, 0.09, 1.57, 3.44, and 0.34% for N, P, K, Ca, Mg, and 167.2, 32.7, 26.1, 28.0, 48.4 mg kg-1 for Fe, Zn, Mn, Cu, and B, respectively. DRIS-derived sufficiency ranges in Lisbon lemon (Citrus lemon) were 1.7-4.2, 0.08-0.14, 1.2-2.5, 3.2-4.5, 0.13- 0.2% for N, P, K, Ca, Mg, and 126.5-274.6, 20.7-29.2, 25.1-112.5, 16.4-31.5, 9.8-56.1 mg/kg for Fe, Mn, Zn, Cu, B, respectively, and also in Perl tangerine (Citrus tangerina) were 1.7-4.2, 0.07-0.12, 1.1-2.1, 2.6-4.2, 4.2-5.0, and 0.6-0.9% for N, P, K, Ca, Mg, and 117.1-217.5, 18.1-47.4, 5.2-50.1, 19.6-32.5, and 22.1-74.7.1 mg/kg for Fe, Mn, Zn, Cu, B, respectively. A comparison of the DRIS method with the DOP showed that Iron for Lisbon lemon and Boron for Perl tangerine gardens had the most negative index values. According to the DRIS index, priorities on the macro and micronutrients were determined for Lisbon lemon as Fe > N > B > K >Mn> Ca > Mg = P > Cu > Zn and for Perl tangerine as B > Fe > K > Cu > N > Ca > Mg >Mn> Zn > P. Based on DOP index, priorities on the macro and micronutrients were determined for Lisbon lemon as Fe > K > B > Cu > Mn > Ca > N > P > Mg > Zn and Perl tangerine as B > Zn > Fe > N > Mn > P > K > Mg > Ca > Cu. However, priorities on the nutrients were different in DRIS and DOP methods for both gardens except for the first priority. The efficiency of DRIS and DOP methods of this study compared to previous research on the priority of certain nutrients can be related to plant nutrition management, plant type, and climatic conditions of the study area. In general, nitrogen and potassium were the most deficient for both gardens, and among the micronutrients Iron and boron had the highest deficiency for both gardens. Overall, nitrogen, potassium, iron, boron, and priority nutrients should be given special attention to their nutrition.