臺灣主要水田土壤生產力及兩期作產量之比較研究

Abstract

Rice yield is higher in the first than in the second crop in Taiwan and the difference is larger in the southern part of Taiwan. Temperature and solar radiation are known to be the main factors causing such yield difference. To ascertain whether soil properties have any influence on the low yield of the second crop, a greenhouse expriement was carried out succesively for three years by using six representative paddy soils which included: a sceist alluvial soil from I-Lan, and acid latosolic soil from Tou-Yuan, a slate alluvial soil (alkine) from Chung-Hwa, two sandstone and shale alluvial soil from Tainan (one fine textured and one medium textured), and a slate slluvial soil (acidic) from Ping-Tung. Rice was planted in these soils for two crops each year and soil solution was analyzed at two-week intervals during the vegetative phase of the rice plant to understand the chemical changes in soil solution and its relation to rice yield. The result is summarized as follows: 1. The schist alluvial soil from I-Lan: The soil was brought back from the area where suffocation disease was common. After planting rice in the green-house for one or two crops, K+ content increased but the content of reducing substances such as oxidizable matter, organic acid and HCO3- decerased markedly in the soil solution. As a result, the rice yield increased and even surpassed that grown in the high yielding paddy soils of southern Taiwan. Rice yield depends more on the amount reducing substances in the soil solution rather than the crop season in this soil. 2. Acid latosolic soil from Tou-Yuan: Rice yield in this soil was the lowest among these six representative soils. Though straw yield was higher in the first than in the second, there was no difference in grain yield. Low pH, low available phosphorus content, high phosporus fixing capacity and high water soluble iron content were the main reasons attributable to the low yield of this soil. Liming and application of phosphate fertilizer were believed to be the remedy method but neither could markedly increase its yield. It was found that organic manure could improve the productivity of this soil better than liming, especially in the first rice crop, and the influence was mostly due to the improvement of the physical, rathan than chemical, condition of soil. 3. Soils from central and southern Taiwan: These four soils all gavo higher rice yield in the first than in the second crop, and the specific conductance, NH4+, K+ content of the soil solution were also higher in the first crop season. It was found that rice yield was positivey correlated with the NH4+ content in the soil soulation, especially in the second crop. Rice yield of the second crop was best predicted by the combination of NH4+ content in the soil solution at 0, 2, 6 and 8 weeks after transplanting (R=0.91**). These results showed that rice yield of the second crop might be increased by increasing the NH4+ content in the soil solution of these soils.