Graduate Thesis Or Dissertation
 

Diagnostic approaches to evaluate nutrient status, partitioning, mineral dynamics, and relationships with yield and fruit quality of 'Valencia' orange trees

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  • Five nutritional aspects of 'Valencia' orange production in Agadir, Morocco during 1989-1991 were evaluated: 1) the effect of N and K on yield and fruit quality, 2) leaf sampling time and diagnostic approaches to optimize mineral nutrition, 3) mass and mineral partitioning within individual trees, 4) K-Rb relationships, and 5) Ca-Sr relationships. 1. Applications of N increased yield in 1991 but 1600g N/tree did not increase it over 800g N/tree. Fruit diameter, length, and weight were decreased in 1991 by 1600g N application. Firmer fruit were produced by unfertilized trees. Applications of 1600g K/tree/year delayed color in 1991. 2. Leaf N, P, K, and nutrient ratios and products varied with time. The least variation occurred in September-October. The highest percentages of diagnostically important leaf nutrients, ratios, and products were obtained in October. Among all nine N-K treatments, 1600-0 gave the lowest NII and highest yield and inversely for 0-1600. Correlations of leaf nutrients and their DRIS indices with tree yields varied with time and followed similar patterns. Nutritional imbalance index (NII) correlated inversely with yield and peaked in October. Both ratio-based and sufficiency-based approaches provided similar information. 3. Dry matter and mineral nutrient partitioning varied among various tissues. The greatest portion of K and P was located in fruit, while that of N, Ca, Mg, Rb, and Sr was located in leaves. Among the macroelements, only leaf N concentration was highly correlated with total N tree content. 4. Applications of K and Rb increased K and Rb in various tissues. The K:Rb ratios were tissue-dependent. They were lowest for leaves and highest for fruit irrespective of treatment. Compared to K, Rb was allocated to leaves in relatively large amounts, with smaller portions being partitioned into fruit. Applications of K increased leaf K, decreased leaf Rb, and increased leaf K:Rb ratios. Seasonal changes of leaf K and leaf Rb were not similar. As leaf K increased, leaf Rb decreased, and vice versa, making K:Rb ratio less stable over time than either leaf K or leaf Rb. Although qualitatively useful, K:Rb ratios do not appear to be useable to study K dynamics. 5. Nitrogen decreased leaf Sr but did not affect leaf Sr:Ca ratio. Potassium had no effect on leaf Ca, Sr, and Sr:Ca ratio. Calcium and Sr concentrations varied with tissues. Strontium:Ca ratio was particularly low in fruit and flower compared to other tissues. Fruit discriminated against Sr. The use of Rb:K or Sr:Ca ratio as a means of tracing K or Ca uptake and movement within an orange tree is probably not feasible.
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