Response of azolla to phosphorus, potassium and zinc in different paddy soils [Philippines]
1984
Ali, S.
A pot culture test in greenhouse was performed to know the P, K or Zn deficiency and azolla response for increasing the azolla biomass production and its N2-fixation. Eleven rice soils of the Philippines belonging to seven different textural classes, ranging from loamy sand to clay, with pH range of 4.7 to 7.7 were used. In each soil -PKZn, -P, -K, -Zn and +PKZn treatments were made. The investigation showed that the concentration of P, K and Zn in flood water dropped rapidly during the first week after their application, and decreased very slowly during 2nd and 3rd week indicating that equilibrium was attained in one week. The flood water P concentration after 1 week gave highly significant relationship with NaHCO3 P/EDTA + NaHCO3 P ratio, while K concentration with K intensity factor and exchangeable potassium percentage in these soils. To obtain high azolla yield a balanced nutrition with the following combination of nutrients land their ratio in floodwater after 1 week was needed: P more than 0.15 K/P ratio less than 45, Zn/P ratio less than 1.1, and probably K 3.3-13 ppm and Zn 0.06-0.18 ppm. P deficiency mostly occurred in low to medium azolla producing soils, while K and Zn deficiency was limited only to 2 high azolla producing soils, indicating that major factor limiting azolla growth in these eleven soils was P, followed by K and Zn
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