AMELIORATION OF ZINC DEFICIENCY OF CORN IN CALCAREOUS SOILS OF THAILAND: ZINC SOURCES AND APPLICATION METHODS

A variety of zinc (Zn) fertilizer sources are applied with varied responses on calcareous soils in Thailand. Seed treatment is an alternative method to deliver Zn to corn and alleviate Zn deficiency. To address this Zn delivery methods we conducted greenhouse studies on corn grown in three calcareous soils of Thailand to three Zn fertilizer sources [zinc sulfate (ZnSO₄), Zn-ethylenediaminetetraacetic acid (EDTA) and Zn citrate]. We also evaluated effectiveness of soaking corn seed in three concentrations of ZnSO₄ (0.4, 0.8 and 1.6%) prior to planting compared to soil applied methods. Applications of zinc increased the growth, dry matter yield and zinc uptake of corn with few differences observed among the types of fertilizers. Seed soaking with ZnSO₄ solution also increased Zn uptake, growth rate and yield comparable to soil-applied Zn. Seed soaking prior to planting is an effective and efficient method to supply Zn to corn grown in Zn deficient calcareous soils of Thailand.     

DISTRIBUTION AND PHYTOAVAILABILITY PREDICTION OF ZINC IN AGRICULTURAL CALCAREOUS SOILS

The extractability and distributions of zinc (Zn) were evaluated in calcareous agricultural soils from South-West Iran. Both single [diethylenetriaminepentaacetic acid (DTPA)] and sequential extraction procedures (Singh scheme) were applied to 20 representative soils. The DTPA extractable zinc levels were low (on average 3.34%). The sequential extraction procedures were also utilized for the study of zinc phytoavailability in maize plants (Zea mays L.) in a greenhouse experiment. The Singh scheme was significantly better than DTPA plus soil properties in phytoavailability prediction of zinc in soils. Significant correlations were found between the amounts of DTPA extractable zinc and the iron (Fe) oxides-bound (AFe and CFe) and residual fractions extracted by the Singh procedure. Zinc concentrations in plant samples (mean value of 27.49 mg kg^?1) were poorly correlated with the different extracted soil fractions (single and sequential). The Singh procedure provided better predictions of zinc uptake by plants than DTPA extraction method.     

COPPER TOXICITY AND ACCUMULATION IN POTTED SEEDLINGS OF THREE APPLE ROOTSTOCK SPECIES: IMPLICATIONS FOR SAFE FRUIT PRODUCTION ON COPPER-POLLUTED SOILS

A 190-d pot cultivation of three apple rootstock species, Malus hupehensis, M. prunifolia, and M. micromalus, was conducted to investigate tolerance, uptake and accumulation of copper (Cu) in different rootstock species. The calculated soil Cu concentration that reduced plant biomass by 50% decreased in M. hupehensis, M. prunifolia, and M. micromalus. This experiment showed that Cu tolerance of M. hupehensis was superior to the other rootstocks. Copper accumulation proportions in shoots or leaves of M. hupehensis were only 0.7–7.4%, which were the lowest among the three species in both control and Cu treatments, and especially were as low as only 40–50% of those of M. prunifolia. The results indicate that Cu-tolerant low-aboveground-Cu-accumulation rootstocks (i.e., excluder rootstocks) could be a good alternative to produce safe fruits with low Cu concentration on Cu-polluted soils without a complete ban on Cu fungicides.     

土壤持水特征测定中质量含水量、吸力和容重三者间定量关系Ⅰ. 填装土壤

在试验过程中，通常采用一个土样进行连续试验来测定土壤的持水特征。此时，土样的有机质、黏粒矿物类型和阳离子交换量等性质基本保持不变，而土壤的容重在水力学和机械压力共同作用下会发生很大的变化。因此，我们认为实测的土壤持水特征不再是土壤吸力和含水量相对应的一条曲线，而是由土壤质量含水量、吸力和容重三变量共同确定的一个曲面。本文在Brooks—Corey土壤水分特征曲线模型的基础上，提出了两种描述土壤质量含水量、吸力和容重三变量关系的曲面模型，分析了模型的优缺点和适用条件，并采用离心机石蜡控容重法实测了四种质地填装土壤的三变量特征曲面。研究结果表明：土壤持水特征是由土壤质量含水量、吸力和容重三变量共同确定的一个曲面这一假设是合理的；类似于Brooks—Corey模型的两种幂函数经验曲面模型能够合理地描述填装土壤的实测数据，决定系数均大于0．94；模型Ⅰ的拟合效果略好于模型Ⅱ，但模型Ⅱ包含两个物理意义明确的参数，具有一定的优势。这一研究将为校正容重变化对土壤水力学参数的影响提供新的途径。