Rice (Oryza sativa L.) seedling-chlorosis correction by Fe, Zn, and H₂SO₄ applications

Abstract

In the western Texas rice belt (Coastal Prairies) rice seedling chlorosis in calcareous spots and cut areas has recently become more prevalent. Field investigations were conducted regarding the feasibility of rice seedling chlorosis correction by soil surface application of H₂SO₄ or different Fe and Zn fertilizer materials. The capabilities of these materials to ameliorate the conditions and prevent the serious mortality in the seedling stage, thus resulting in a vigorous plant population, were analyzed. Chlorotic soil analysis showed higher HCO₃, Ca and pH levels but lower Fe than the normal rice producing soil. However, the DTPA extractable soil Fe and Zn levels rated high according to soil tests established for upland crops, notwithstanding, Fe+Zn deficiencies occurred on rice. The micronutrient fertilizer treatments indicated the effectiveness of 5 to 10 kg of Zn, 40 kg of slow release Fe, or 100 kg of Fe as sulfate each applied alone. Greater yields were obtained from lower combination rates of Zn and Fe that proved to provide maximum rice seedling chlorosis correction and yields almost triple that of the check treatment. Most sources of Fe tested proved effective at high rates except the Fe chelate. The H₂SO₄ appeared consistently effective and superior to Fe and Zn applications as in previous tests. Since the rice seedling chlorosis was evidently a Zn + Fe deficiency, the higher H₂SO₄ rates apparently released native soil Zn + Fe equivalent to the most effective fertilizer combinations. The H₂SO₄ changed soil characteristics proportional to the application rate. Soil surface pH was initially lowered to slightly acid levels. The soil extract EC and extractible Zn, Fe, Mn, and Cu were increased by acid application. However, a reversion of the extractable micronutrients to fixed forms was indicated, although evidently in forms still available to rice plants..