Micronutrient availability to cereals from calcareous soils

Summary On several alkaline calcareous soils, Zn and Cu deficiency occurred mainly in lowland rice (Oryza sativa L.) and was rarely found in wheat (Triticum aestivum L.). Zinc and Cu requirement of plants was not responsible as the critical Zn and Cu contents in tops of the two plant species were almost similar i.e. 17.4, 6.5 and 14.5, 5.6 ppm respectively. Neither did rice absorb Zn and Cu less efficiently. On the contrary, their rates of absorption in rice were double than in wheat. They were 22.2, 6.3 and 10.2, 3.3 ng atoms/g fresh root/h respectively in the two plant species. Flooded soil conditions appeared to be responsible for Zn and Cu deficiency in rice as their deficiency was found mainly in plant samples collected from continuously flooded fields. The mechanism is not known.Both Zn and Cu inhibited uptake of each other in wheat on most of the soils. In rice, only applied Zn depressed Cu uptake but Cu had generally little effect on Zn uptake. Little Cu inhibition of Zn uptake in lowland rice seems to be related to flooded soil conditions. The mechanism is yet to be known. The antagonising element accentuated the deficiency of the other element both in wheat and rice and severely reduced their yields on soils marginal to deficient in Zn or Cu supplies. It is recommended that their soil availability status should be thoroughly considered before their fertilizers are applied. re]19750515