Finch, Calvin Robert (1993-02). Sulfur nutrition requirements of Prunus persica (L.) Batsch. Doctoral Dissertation.
Prunus persica (L.) Batsch performance was studied under various sulfur nutrition regimes and fertilization tactics in greenhouse and field experiments after a simplified digestion process for foliar samples was established. The closed vessel microwave procedure requires less than 2 hours to produce 12 digested 0.5 g samples from the point of weighing the samples to applying them to plasma emission spectrometry analysis. The procedure utilizes nitric acid and hydrogen peroxide as a predigestion. The predigested samples are then each microwaved for 2.25 minutes. With this procedure, sulfur levels are within an average of 1.27% of that reported for the NBS Citrus Standard, are within 102.25 to 99.44% of the values determined for wet ash digested materials and display recovery rates of 96 to 98% for known levels of sulfur in the range expected in plant foliage. Sulfur sufficiency and deficiency levels were determined through two greenhouse experiments using Nemaguard. Lovell. Montclar and Nemared rootstock seedlings. The sulfur sufficiency level for p each rootstock seedlings grown in the greenhouse is 1400 to 2000 ug S/g DW foliar S. Severe deficiency symptoms, including necrosis, were visible at levels below 90 ug S/g DW in plants with mean foliar S levels between 550 and 700 ug S/g DW. S fertilization experiments on mature trees on low an d high soil test sulfur soils in East Texas determined that, like the seedlings in the greenhouse, mature trees were very efficient at obtaining enough S to reach the sufficiency level for the nutrient. Applying ammonium sulfate and sulfate potash of magnesia ground fertilizers, and ammonium thiosulphate and 21-7-7-14 foliar fertilizers raised foliar S levels in nearly half the treatments but foliar S levels in the range reached had minimal relationship to growth or appearance ratings. The levels of N. P, K, Ca, B, Zn, Fe and Mn showed greater correlation to growth and appearance than did S levels.