Status of slowly available K in soils

For perennial fruit trees, slowly available K rather than readily available K is considered in nutrient management and fertilization programs in Hainan province. Soil testing in a mango production area in Hainan revealed that loam soils accounted for 53%, sandy soils for 33%, and clayey loam soils for 14%. Slowly available K in the soils ranged from 14 to 813 mg/kg...with an average of 255 mg/kg (Table 1). Soil samples predominately (82%) had low slowly available K values. Of the remaining soils which were considered high in slowly available K, the majority came from an orchard where the grower applied burned straw ashes. The data below suggests that the mango fields were virtually all deficient in K.

Table 1 The soil content of slowly available K in mango orchards

Nutrient status in mango leaves

According to B.W. Cull and E. C. Winston (1983), the adequate nutrient levels for mango are given in Table 2. For comparison, leaf nutrient status for plants analyzed in Hainan are shown in Table 3. This data shows that 3.6% of the mango was deficient in N, none were P deficient, 23.4% in K, 2.4% in Ca, and 54.8% in Mg, respectively. Thus for mango production, Mg and K are the key nutrients to be taken care of in fertilizer program on the island.

Table 2 Nutrient critical level in mango leaves (g/kg)



Table 3 Nutrient status in mango leaves ( % of total samples)