Abstract: The utilization of energy in agroecosystems of south subtropical Tongan county in Fujian province was investigated and analysed. Three subecosystems were included: crop, orchard and forest, and livestock subsystem. The results showed that: (1) The total amount of solar radiation in these ecosystems was 4.396?10¹⁶J, of which,5.07?10¹⁵Jwas in cultivated land and 3.62?10¹⁶Jin hilly region. (2) The utilization efficiency of solar energy was 2.86% for sugarcane and under 1% for other crops. (3) In total energy investment to cropland, the organic energy input took part of 81%, which was averagely 4.49 times as much as inorganic energy invested. (4) The relationship between output/input ratio and organic energy/inorganic energy ratio was that of a quadratic parabola.

Key words: Sewage sludge, Land utilization, Crop, Soil, Environmental impact