Effect of nitrogen and salinity levels in the nutrient solution on the DRIS diagnosis of greenhouse tomato

Abstract

Norms for the Diagnosis and Recommendation Integrated system (DRIS) developed for greenhouse tomato (Lycopersicon esculentum L.) were evaluated experimentally by varying the N concentration (115, 243, and 443 mg N L^‐1 ) or the salinity level (1.4, 2.5, and 3.7 dS m^‐1 ) of the nutrient solution. Foliar samples were taken at different intervals during the season for total N, P, K, Ca and Mg analysis. The nutrient imbalance index (NII) was calculated by summing up DRIS indexes irrespective of sign. A dry matter index (DM) was included in the modified DRIS (M‐DRIS) approach as a separator between excessive or deficient nutrients. Yield of marketable fruit that accumulated over a 8 week harvest period was quadratically related to N fertilization: 115, 243, and 443 mg N L^‐1 produced 2.9, 3.3, and 2.3 kg per plant respectively. Larger than critical NII values, 82 days after transplanting, were associated with excess of N, and Mg, and Ca deficiencies. Contrary to the DRIS and M‐DRIS approaches, the critical nutrient range approach (CNR) did not indicate any N excess. In the salinity experiment, marketable yield decreased linearly with salinity: 1.4, 2.5, and 3.7 dS m^‐1 produced 3.3, 2.9, and 2.3 kg per plant, respectively. Increasing salinity caused an increase in the NII at all sampling periods. However, Nil's were always smaller than the critical NII and were inconsistent with the low yields obtained. Thus, NII was considered a poor indicator of the salt effect.