Abstract
We designed several fertilizer saving systems for the paddy rotation system using a non-tillage direct seeder. In these fertilizing systems, a sufficient amount of phosphatic fertilizer (fused phosphate) is applied before sowing wheat, and potash fertilizer is applied as top-dressing for wheat and barley. Soybean and rice are cultivated without phosphatic and potash fertilizer, and the total amount of phosphatic and potash fertilizer through the rotation system is expected to be substantially reduced. We examined the effects of these fertilizer saving systems on the productivity of wheat, soybean, barley and rice, and on the chemical properties of the soil for four years. Even when the application rate of phosphatic and potash fertilizer was reduced to 55–80% and 30–55% of that used in the conventional plot, respectively, the yields of all four crops were comparable to those obtained by the conventional system. The available phosphate level in the soil was also comparable to that in the control. Exchangeable potassium in the soil in the fertilizer saving systems, however, was lower than that in the conventional system, suggesting that the potash saving rate needs to be reduced. In addition, pH and CEC were lowered by the continuation of the paddy-upland rotation, although these were not direct effects of the reduction of fertilizer. Further studies are needed to establish an effective and sustainable fertilizing system including management of alkaline materials and organic matter.
