Phosphatic guano combined wit~. steel slag. as effective way for direct application of phosphatic guano to acid soil

Abstract

Phospbatic guano is solidify of sea bird excrement and solidify of bad excrement which their nitrogen have been leached, and steel slag is by-product formed in the process of steel manufacturing. Phosphate fixation and other problems in acid cause low efficiency of phosphatic guano fcrtiJizer in acid soil. However, application of pbosphatic guano combined with calcite or dolomite reduces dissolution of phosphatic guano, which in turn decreases its effectiveness. The objectives of this experiment were 1) to evaluate the combined effect of phosphatic guano and steel slag on plant growth and chemical properties of soil and 2) to study the mechanism of combined effect of phosphatic guano and steel slag. In experiment I, phosphatic guano combined with steel slag significantly enhanced the growth of komatsuna, to an extent not significantly different from that of FMP with dolomite or SP with dolomite. Moreover, the response of komatsuna to this treatment was significant compared to combinations of phosphatic guano and dolomite. More P and B were available in soil on treatment with phosphatic guano and steel slag than phosphatic guano and dolomite. The excellent effect of phosphatic guano combined with steel slag relative to that of phosphatic guano with dolomite was attributed to the superiority of the former in supplying P and B. In experiment 11, steel slag adjusting soil pH to S.S combined with phosphatic guano at a PAC of 10% produced the highest yield and P uptake of komatsuna. Although the plant responded to either steel slag or phosphatic guano, the response to their combination decreased with the increasing amount of.steel slag from that adjusting the soil pH to 5.5 - 6.5 or decreasing amount of phosphatic guano. The P availability in soil with this combination was increased as the amount of the steel slag was reduced or the amount of phosphatic guano was raised, though neither the steel slag nor phosphatic guano raised the available P in soil. In addition, steel slag enhanced soil pH, exchangeable Ca and Mg as well as available B, Mn and Fe, whereas phosphatic guano enhanced only exchangeable Ca. The best response of komatsuna to combination of steel slag adjusting the soil pH to 5.5 and phosphatic guano (PAC of I 0%) was associated with favorable Mg and B supply from the steel slag and P supply from phosphatic guano. In experiment III, silicate ion enhanced the solubility of phosphatic guano in 0.01 N KCI through the anion exchange process, while Ca ion reduced .the solubility of phosphatic guano in 2% citric acid. It was suggested that the mechanism of the combined effect of steel slag and phosphatic guano as follows. Reaction of the steel slag in the soil produced Ca, Mg and other cations in addition to silicate, borate and other anions. The silicate ion exchanged for the phosphate ion of calcium phosphate mineral in phosphatic guano, thus increasing the release of phosphate from phosphatic guano, which in tum increased the concentration and the availability of P in the soil. On the other hand, Ca ion from the steel slag shifted the equilibrium between soluble Ca and phosphate ions with calcium phosphate mineral towards calcium phosphate mineral, thus reducing the phosphate release from phosphatic guano. Increasing soil pH on addition of the steel slag also reduced the solubility of calcium phosphate mineral in phosphatic guano. Moreover, the slag improved supply of Mg and B to plants.