Potassium and Phosphate Nutrition of Pineapple in Relation to Nitrate and Carbohydrate Reserves

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Abstract
In the pineapple plant a low reserve of nitrate was found adequate for greatest possible yields of fruit when carbohydrates were low. In contrast, when carbohydrates were high maximum production was not obtained unless the plants were essentially filled to capacity with nitrate. In practically the same location a difference of 75% in N requirements was found in successive yrs. When the conc. of carbohydrates is low and relatively little nitrate therefore supplied, phosphate is freely absorbed, even from soils rather low in P. In the same site under environmental conditions more favorable for carbohydrate accumulation more nitrate is needed. With higher nitrate there is a proximately corresponding suppression of phosphate absorption, so that it becomes necessary to apply phosphate. The required level of nitrate nutrition, which varies with opportunity for carbohydrate accumulation, is intimately associated with K requirements. Under field conditions in Hawaii, nitrate is not absorbed freely by the plant when K is low. When carbohydrates are high, and relatively much nitrate therefore required, additional K is necessary for nitrate absorption, above that necessary for other functions that K performs. Even in the same site the amt. of potash required varies with weather conditions from year to year. In plants growing on soils notably low in K and P there was seemingly an interplay of compensating relationships. When K was low and absorption of nitrate was'' in consequence limited, carbohydrate accumulation was also curtailed. In turn, although no phosphate was applied, the low level of nitrate permitted fairly free absorption of phosphate. This apparently resulted in a condition of proximately balanced multiple deficiencies and greatly reduced size of plant and fruit. But, except for size, the plants were much the same in appearance as others with more liberal fertilization, and the fruits were about the same in physical characteristics and in % of sugars and total acid as those from plants with a more abundant nutrient supply. P is necessary in relatively high conc. just prior to and during blossom-bud differentiation. or severe losses in yields occur. An adequate supply of nitrate in relation to carbohydrates is also essential at that time. Application of phosphate to plants high in P and deficient in nitrate might well bring about still further nitrate deficiency and decrease in yields, although the suppressing action of even high concs. of phosphate on nitrate absorption is less common than that of nitrate on phosphate intake.