Abstract: The structure and economic effect of agroecosystem models of the flatlands at Qiaotou,Dongguan,Guang dong,were studied,while typical ag roecosystem models of the flatlands in its vicinity were al so analyzed.It was found that the major models of the flatlands in Q iaotou included the integ rated growing_raising model and monocultural v egetable_g rowing model.The results show ed that the inte g rated grow ing_raising model had a perfect functio n and high w ork day value.Accor ding to eco_engi neering principles it w as sug gested that,essential components such as pond fish and livestock should be added to the monocultural vegetable_grow ing model in order to obtain a sustainable effect.

Key words: paddy soil chronosequence, cultivation age, organic carbon, particle size distribution.