粤西砖红壤的镁素状况及其有效性

研究结果表明,粤西砖红壤的全镁含量普遍较低,玄武岩和花岗岩发育的土壤,全镁含量多在0.2％以下,浅海沉积物发育的土壤,全镁不足0.1％,玄武岩发育的土壤,交换性镁较丰,表土含量均在100ppm以上,镁饱和度较高;浅海沉积物和花岗岩发育的土壤,交换性镁贫缺,表土平均含量分别为16.7和14.7ppm,镁饱和度大都极低.土壤供镁能力的强弱依次是:玄武岩发育的砖红壤>浅海沉积物发育的砖红壤>花岗岩发育的砖红壤。交换性镁及镁饱和度与牧草的相对产量、吸镁量以及玉米小苗的含镁量、吸镁量的相关性达显著或极显著水平。据此初步认为可用作土壤镁素诊断指标。酸深性镁的有效性也较高,但因其释放速度较慢,不宜作为诊断指标,可用以评价土壤有效镁的补充能力。

MAGNESIUM STATUS AND AVAILABILITY IN LATBRITE OF THE WESTERN PARTS OF GUANGDONG PROVINCE

Twelve soils derived respectively from basalt, granite and seashore deposit were collected and cropped with grass (Coasteross-1 Pertrudagrass ) and corn in the greerhouse.The soil analysis data showed that all soils tut one bad relatively low content of total Mg. The soils derived from basalt were rich in exchangeable Mg( more than 100 ppm Mg in the top-soils ) .The soils derived from granite and seashore deposit were poor in exchangeable Mg. (ranging from 11.1 to 25.3 ppm in the topsoils) . There were significant correlations among different forms of magnesium.Exchangeable Mg in the topsoils correlated significantly with soil pH and CEC. Mg concentration in the grass and corn was well correlated with Initial total Mg, acid soluble Mg, exchangeable Mg and Mg saturation of CEC.Its correlations with exchangeable Mg and Mg saturation of CEC were much more significant. So was-the total Mg removed ty these two crops. Acid soluble Mg was available to the grass and corn,but its release was too slow to meet the requirement of plant growth.It waa concluded that exchangcable Mg and Mg saturation of CEC are better indices for evaluating the magnesium availability of the soils and the effects of magnesium fertilizer on plant growth .