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Effect of Lime, Organic Matter and Phosphorus on Soil Acidity, Phosphorus Adsorption and Growth of Corn (Zea mays L.) in Ultisols of Central Vietnam
Abstract:
Soil acidity and phosphorus deficiency are major constraints in yellowish-red upland soils of Vietnam and despite such adverse pedological conditions, this kind of soil resource is gaining importance as food production areas due to increasing population. This study was conducted on two acid upland soils namely, a yellowishred soil on diorite rock and a yellowish-red soil on acid igneous rock of Thuathien Hue province and Quantri province, respectively. The objectives of this investigation were as follows: (1) to classify two yellowish-red upland soils of Central Vietnam using the US Taxonomic Classification System, (2) to characterize the phosphorus sorption capacities of two yellowish-red soils of Central Vietnam, (3) to determine the effects of lime and organic matter additions on the pH and different forms of soil acidity of a yellowish-red soil, (4) to compare the effects of lime, phosphorus and organic matter additions on nutrient uptake, growth and dry matter yield of corn on a yellowish-red soil, and (5) to assess the level of lime and phosphorus for best possible corn growth and yield on these soils.
Two laboratory studies were conducted to ascertain the classification of two yellowish-red upland soils of Central Vietnam by using the US taxonomic classification system and to characterize the phosphorus sorption capacities of these soils. A greenhouse and a field experiment were conducted using Xuanloc clay to determine the effects of lime, organic matter and phosphorus on pH, forms of soil acidity, nutrient concentration, nutrient uptake, corn growth and corn yield, and to assess the level of lime and phosphorus for best possible yield.
By using the key to soil taxonomy framework, Xuanloc clay of Thuathien Hue province was classified as fine clay, kaolinitic, hyperthermic, Typic Kanhaplustults while the Huonghoa clay loam of Quangtri province was a fine loamy, kaolinitic, hyperthermic, Inceptic Haplustox.
Xuanloc clay had greater capability to sorb P than Huonghoa clay loam. The adsorption maximum values based on the Langmuir adsorption isotherm equation were 714 mgP/100g and 666 mgP/100g, for Xuanloc clay and Huonghoa clay loam, respectively, while the energy bonding values were 0.0116 and 0.0034 in the same order.
In the greenhouse, the addition of lime, phosphorus, and organic matter on Xuanloc clay significantly increased exchangeable Ca, pH, and it also resulted in higher CEC, and available P. On the other hand, there was a significant reduction in exchangeable Al, solution Al and Al saturation, and exchangeable acidity. The application of 4 tons CaCO3/ha reduced exchangeable Al by about 77 percent. Increasing the lime rate to 8 tons CaCO3/ha completely neutralized the exchangeable Al. The organic matter rates of 5-10 tons/ha increased the available P by 23.3 percent and 30 percent, respectively. Most of the soil chemical properties at 4 tons CaCO3, 180 kg P2O5, and 5 tons organic matter per hectare were optimum for high corn yield. The highest dry matter yield of corn was associated with the following concentration of nutrients in the tissues: 0.18, 2.14, 0.27, 0.33, and 0.02 percent of P, K, Ca, Mg, and Zn, respectively.
Under field condition, liming and phosphorus application significantly increased the grain yield of corn. The application of 6.4 tons of CaCO3/ha about 90 percent relative grain yield compared to 71 percent in the zero-lime treatments. A 180 kg P2O5 /ha resulted in a 90 percent relative grain yield. The grain yield of corn was positively associated with P uptake. The highest grain yield was obtained in the treatment where the soil was adjusted to pH 5.4 and had received 180 kg P2O5/ha.