Potassium, zinc, calcium and magnesium interactions in lowland rice [Philippines]
1988
Navarro, A.A.
An increase in grain yield of 1.6 t/ha in WS (wet season) and 4.0 t/ha in DS (dry season) in San Manuel silt loam, and 0.9t/ha in WS and 0.7 t/ha in DS in San Manuel Silty clay were obtained when K was applied at 100 kg/ha. Zinc application up to 60 kg/ha significantly increased grain yield only in San Manuel silt loam in WS. Potassium content and uptake increased with increasing K application level. Zinc content and uptake also increased with increasing Zn application. Calcium and Mg content and uptake decreased with increasing K application. Uptake was increased with 100 kg K/ha but higher application levels reduced Ca and Mg uptake. Exchangeable K increased with increasing K application. Values were higher at maximum tillering stage. Available Zn at maturity in treated plots remained in adequate levels. Exchangeable Ca and Mg remained unaltered with K-Zn application. The highest K uptake at maturity in both seasons ranged between 126-429 Ca + Mg/K ratio while highest Zn uptake was obtained with 5-50 Ca + Mg + K/Zn ratio. There was Zn, but not K fixation in both soils. Zinc fixation was higher in San Manuel silty clay. Potassium response of field-grown rice is higher when initial exchangeable K is much lower than 0.20 meq/100 g soil. Hence, K should be applied to raise the exchangeable level to the desired value. Zinc application level should not be based entirely on Zn status in the soil, but varietal response to Zn should also be considered. Further, soil cation ratios can roughly predict availability of said cations. Potassium availability is greater with lower Ca + Mg/K ratio while Zn becomes more available with lower Ca + Mg + K/Zn ratio.
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