INFLUENCE OF N-P-K FERTILIZATION ON INCIDENCE AND SEVERITY OF OXIDANT INJURY TO MANGELS AND SPINACH

Experiments were performed to study the influence of nitrogen, potassium, and phosphorus on the sensitivity of plants to photochemical oxidant damage. Mangels and spinach were used as the test plants. Approximately equal amounts of ammonium and nitrate nitrogen were used with (NH/sub 4/)/sub 2/SO/sub 4/, KNO/sub 3/, and NH/sub 4/NO/sub 3/ as the sources. Phosphate was added as Ca(H/sub 2/PO/sub 4/)/sub 3/. Potassium was added as either KNO/sub 3/ or K/sub 2/SO/sub 4/. The results of fumigating the differentially fertilized plants revealed that nitrogen had a pronounced effect on the sensitivity of both mangels and spinach. The severity of injury increased significantly as the nitrogen level was increased. There were significant interactions of nitrogen with phosphorus and between phosphorus and potassium on the severity of injury. Phosphorus additions produced poor top growth that was somewhat resistant to oxidant injury. Increasing the potassium had no measurable influence on leaf production but seemed to increase the severity of damage at a low nitrogen level when P was also low but not when P was at a higher level.