Influence of soil reaction and applications of zinc on yields and zinc contents of rice plants

The yield of rice was significantly reduced when the soil reaction exceeded pH 7.0. Further significant yield decreases were obtained when Crowley silt loam was adjusted to pH 7.5 with, dolomitic limestone. A highly significant quadratic relationship was found between the yield of rice and soil reaction (pH). The soil pH accounted for 45.77. of the variability in yield. A highly significant positive linear relationship was found between yield and Zn extracted from the soil with DTPA‐TEA. Extractable Zn accounted for 42.2% of the variability in yield. Significantly lower rice yields were obtained on soils that did not receive supplementary Zn and contained less than 1 ppm of extractable Zn. Increasing the soil reaction from pH 6.5 to pH 8.0 resulted in a significant linear reduction in Zn extracted from the Crowley soil with DTPA‐TEA. A critically low level of soil‐Zn was found when the soil reaction was adjusted to pH 7.5 and no Zn was applied. A highly significant curvilinear relationship was found between the concentration of Zn in rice leaves and extractable soil‐Zn. Approximately 23% of the variability of leaf‐Zn was accounted for in the extractable Zn content of the soil. Data were presented that indicated that DTPA‐TEA extractable soil‐Zn and the Zn concentration in the ‘leaves of rice plants at the 2 mm panicle stage of development may be used as an effective diagnositc technique in determining the Zn‐nutrient status of the soil and plant.