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- Author or Editor: Sparks Darrell x
Response from foliar-applied P (0.0%, 0.50%, 0.75%, or 1.00% P from KH2PO4) was compared to that from root-supplied P (Hoagland's solution) in pecan [Carya illinoinensis (Wangenh.) C. Koch] seedlings. Compared with no applied P, foliar-applied P suppressed or prevented P deficiency symptoms; increased the P concentration in the leaf, trunk, and root; and increased tree growth. However, P in all 3 organs and growth of plants treated with foliar sprays were less than for plants with root-supplied P. Furthermore, P sprays eventually produced leaf scorch. Compared to root-supplied P, omitting P affected N, P, K, Ca, Mg, Fe, Mn, B, Cu, Zn, Na, and Al in the plant. These imbalances induced by P deficiency were only partially alleviated by foliar-applied P.
Foliar applied Mg (0.0%, 0.24%, 0.48%, or 0.96% MgSO4-7H2O) was compared to root-supplied Mg (Hoagland's solution) in pecan [Carya illinoensis (Wan- genh.) C. Koch] seedlings. Foliar-applied Mg suppressed, but did not prevent, Mg deficiency symptoms and increased leaf concentration of Mg and seedling growth compared to plants grown without Mg. Leaf Mg and growth from foliar sprays were substantially less than for plants with root-supplied Mg. Compared to root-supplied Mg, omitting Mg increased the leaf concentration of P, K, Cu, and Zn; decreased Ca and Mg; and had no effect on N, Fe, Mn, B, and Al. The nutritional imbalances induced by Mg deficiency were alleviated by foliar-applied Mg.
‘Curtis’ pecan [Carya illinoensis (Wang) K. Koch] seeds were germinated in perlite and treated with either deionized water, a complete nutrient solution or a nutrient solution minus B, Ca, Cu, Fe, K, Mg, Mn, N, P, S, or Zn. All seedlings receiving deionized water died back, 23% died back in the minus B treatment, 82% when Ca was omitted, and none when treated with a complete nutrient solution.
Pecan [Carya illinoensis (Wang) K. Koch] seed were germinated in perlite and treated with either a complete nutrient solution or a nutrient solution minus B, Ca, Cu, Fe, K, Mg, Mn, N, P, S, or Zn. Omitting any single nutrient suppressed seedling growth and induced deficiency symptoms for all nutrients except Fe, Mn, and Cu. Corresponding leaf concentration data associated with deficiency symptoms and normal growth agreed closely with proposed standards.
Studies involving the pecan are needed to determine the relationship of leaf area per unit of fruit to nuts set per cluster, nut size and quality, and alternate bearing. However, these studies are pending a rapid method for estimating leaf area.
The modified Mitscherlich plant growth model was used to quantify the threshold leaf Zn level influencing nut yield and vegetative growth, on an orchard basis, for pecan [Carya illinoinensis (Wangenh.) C. Koch]. Four indices of tree performance, including percentage of trees without deficiency symptoms, vegetative growth, nut yield, and trees without deficiency symptoms plus nut yield, were analyzed with regard to leaf Zn concentration. Data available from published and unpublished sources on any single performance index were combined for mathematical modeling. The threshold value for leaf Zn was determined to be ≈50 μg·g-1 for these tree performance indices. Thus, nut yield and vegetative growth in an orchard will be reduced with a leaf Zn concentration below ≈50 μg·g-1, but will not be affected above this value.
Freezing and damaging temperatures were imposed on `Desirable' pecan [Carya illinoinensis (Wangenh) K. Koch] trees before budbreak and again during the beginning of pistillate anthesis. Freezing temperatures imposed before budbreak resulted in abnormal flowering; freezing temperatures during anthesis did not. Abnormal flowering depends on both a critical temperature (about -1.7 to -2.2C) and a critical stage of pistillate flower bud development within the 8- to 10-day interval before budbreak.
The inter-relationship of precocity, prolificacy, and kernel percentage was studied in pecan [Carya illinoensis (Wangenh.) C. Koch]. Prolificacy was highly correlated with precocity, but the relationship was not one to one. Increased precocity resulted in proportionately smaller increase in prolificacy. Variability in kernel percentage increased with prolificacy.
Effects of applied P on pecan [Carya illinoensis (Wangenh.) C. Koch] were studied in the greenhouse and field. Objectives were to study P effects on vegetative and nut growth, leaf scorch and/or premature defoliation, and nutrition. Elements were analyzed for both total and extractable (2% acetic acid) fractions. In the greenhouse, deficiency symptoms occurred when leaf P (dry-weight basis) was 0.08%; vegetative growth was maximum when P was 0.19% to 0.22%. In the field, applied P increased nut growth and decreased leaf scorch and premature defoliation. Leaf P values for maximum nut growth and minimum leaf scorch and/or defoliation are greater than 0.14% and 0.16%, respectively. Except when P was within the visible deficiency range, applied P had little direct influence on the concentration of other essential elements under either greenhouse or field conditions. Generally, extractable P was a slightly better indicator of the P status of the tree than total P, but the differences are of doubtful physiological significance.
A multiple regression model was developed from historical data, 1945-92, to predict pecan [Carya illinoensis (Wangenh.) C. Koch] production in a humid climate. Variables were production trend (year of production), previous year's production, and climatic indices for the previous and current year. Production trend was used to measure change in production with time. Previous year's production was the index of alternate bearing. Variables for previous year's climate were heating degree-days for April-October and cumulative rainfall during May-July and 1-15 Sept. Variables for current year's climate were cumulative rainfall during April-August and 1-15 Sept. The indicator used for scab [Cladosporium caryigenum (Ell. & Langl.) Gottwald] infection was the highest cumulative sum of 2 or more days of consecutive rain occurring in May, June, or 1-15 July. The R 2 for the model was 0.908. Production trend was the most important factor influencing production during the 1945-92 study period. Importance of the other variables in decreasing order were previous year's rainfall in May-July, consecutive rainy days, previous year's production, current year's 1-15 Sept. rainfall, previous year's heating degree-days, previous year's rainfall for 1-15 Sept., and current year's rainfall during April-August. Previous year's conditions had a greater effect on production than current year's. The recent decline in pecan production in the southeastern United States is due to an unfavorable change in climate.