Magnesium Status In Black Soil Around Harbin And Its Effects On Some Crops

Experiments were conducted with the methods of laboratory analysis and field trial to study the Mg supply capacity in black soil around Harbin and its effects on growth, yield and quality of corn, rice, soybean and wheat. The main results obtained are as fol- lows: 1. Mg supply status in black soil around Harbin. According to the analysis results of 60 soil samples taken from saburbs of Harbin, the total Mg contents was0.26o/Q.o358%, with the average 0.300% ; and exchangeable Mg was 0.6?.lme/l00g with the average 2.l5me/IOOg. The total Mg contents was much higher than the average value around China, but this index has been lowering ob- viously because of no supplement. Though the exchangeable Mg was above critical val- ue, in 11.6% of soil samples that was under line/bOg. In some counties in outskirts of Harbin, one or two crops have shown Mg-deficient symptoms, indicating that some soils were deficient in Mg. If there was no Mg supplement, the Mg in soil would be used up gradually. 2. Mg has great influence on crop yieds. Compared with conventional NPK applica- tion. Mg addition increased soybean yield by 3. 8-11.9Yo, increased rice yield by 3. 8 14. 14, increased wheat yield by 6. 0 11. 9% and increased corn yield by 4. 3 13.3%: 3. Mg can promote the uptakes of N, P and K by crops, accelerate chlorophyll for mation, therefore enhance the capacity of photosynthesis. Compared with NPK applica- tiOn, Mg addition increased concentrations of chlorophyll in wheat by 0. 52?. 0mg g FW at earing stages in rice by 0. 2-. 8 mg gW and 0. >-O. 9 mg gW at tillering and earing stages. Mg application also increased the fresh weight and dry weight of roots and shoots. In addition, Mg can improve grain quality. The protein conteont of soybean increased by 0. 22?. 61% and fat content increased by 0. 05?0.100/0. 1. The effects of Mg fertilizers relate to such factors as the content of exehaneable Mg in soil, R,g, Ca/Mg, and the percentage saturation of Mg in soil. Soil test Should be made prior to Mg Fertilizer application. Both too high (>10kg hm2) and too W 5kg hm) in application rates are not reasonable, and middle rate (around 7. 5 h1 hm) will be appropriate.