The Feasibility Of Steel Slag As Constitutes Of Soilless Culture Medium

Steel slag,a byproduct of steelmaking industries,accounts for 15%-20%of steel production.Steel slag not only occupies land,but also poses risks to the environment.In recent years,although the utilization rate of steel slag has improved in China,it is still lower than in the developed countries.Generally speaking,the utilization percentage of steel slag is pretty low in China,especially in the field of agriculture.Therefore,it is an urgent issue how to use and recycle the steel slag resource in agriculture.The present study aimed at using steel slag as a raw material composition of compound cultivation matrix,and then doing the research of soilless cultivation of Chinese cabbage in greenhouse.The main results are presented as follows:1.Through analyzing 17 kinds of steel slag,we found that the steel slag was alkaline with big bulk density and small porosity,indicating that the steel slag is of high density and high hardness.Generally speaking,Cr concentration of 17 kind of steel slag is beyond the maximum allowable limit.There were significant differences in silicon concentration,while no difference was found in calcium concentration.According to the analytical results,we can conclude that steel slag G(from Anshan iron and steel),I(Unknow),and K(from Shougang)is suitable for making of compound cultivation matrix.2.Using physical and chemical methods to mobilize elemental nutrients in steel slag,on the one hand,we found that the available silicon concentration improved when the mesh fineness increased from 60 to 325.However,no difference was found in available silicon concentration among the treatments with mesh 60,100 or 200.On the other hand,the concentration of calcium was significantly different through grinding.The concentration of available silicon tended to decrease with increasing of nitric acid added at the same particle size level of steel slag.The calcium concentration increased significantly when the nitric acid was added at a rate of 20 ml/100g,however,it decreased when the nitric acid was added at a rate of 40 or 60 ml/100 g.3.According to the results of market survey and achievements of some researchers,we chose the best composite matrix formula,which have the best physical and chemical properties and a good cultivation effect:a)the ratio of garden soil:peat:perlite is 1:3:1;b)the ratio of peat:vermiculite:river sand is 5:3:2;c)the ratio of turf:perlite is 1:1,d)the ratio of peat:vermiculite:perlite is 1:1:1,and e)the ratio of peat:vermiculiteis 2:1.Using the steel slag G,I and K at the proportion of 20%,40%,80%and 100%to replace the vermiculite or perlite in the matrix,we ultimately determined the following steel slag composite matrix formula as compared to their physical and chemical properties:1)Peat:vermiculite(2:1);2)Peat:vermiculite:steel slag G(2:0.8:0.2);3)Peat:vermiculite:steel slag G(2:0.6:0.4)4)Peat:vermiculite:steel slag I(2:0.8:0.2);5)Peat:vermiculite:steel slag K(2:0.8:0.2);6)Peat:vermiculite:steel slag K(2:0.6:0.4);7)Peat:vermiculite:steel slag K(2:0.4:0.6);8)Peat:perlite(1:1);9)Peat:perlite:steel slag I(1:0.8:0.2);10)Peat:perlite:steel slag K(1:0.8:0.2);11)Pea:perlite:steel slag K(1:0.6:0.4);12)Peat:perlite:steel slag K(1:0.4:0.6);13)Peat:vermiculite:perlite(1:1:1);14)Peat:vermiculite:steel slag I:perlite(1:0.8:0.2:1);and 15)Peat:vermiculite:steel slag I:perlite(1:0.6:0.4:1).4.In the pot experiment with Chinese cabbage,we showed that,in general,no significant difference in morphological indexes or nutritional indicators was observed between any composite treatment and its control,with even better performance in some treatments than in control,suggesting that steel slag can replace part of vermiculite or perlite.For example,the plant height and root length of treatment T3,T5,T7,T8 and T9 are better than those of control,while vitamin C and soluble protein contents of treatment T5 and T6 are higher than those of the control.Above all,part of the steel slag can be used as the raw material of compound cultivation matrix instead of vermiculite or pearlite.It is excellent when the replacement ratio is about 20%or 40%.