Based on typical black soil in northeast of China

the proportion of soil solid-liquid-gaseous phase and the concentration of soil available nitrogen

phosphorus

potassium were measured after machinery harvesting and subsoiling.The effect of heavy machinery operation on soil three phases and available nutrient were revealed

it could provide scientific basis for guiding machinery activities and sustainable utilization of black soil resources.The results showed that:(1)It was a new and effective analysis method for soil structure to put soil solid-liquid-gaseous phase in a two-dimensional-three-phase diagram.The variety of three phases and trend to optimal structure would be shown intuitively.(2)The field operated by heavy machinery inclined to the ideal structure intensely.Heavy machinery operation ameliorated soil three phases more distinctly than medium machinery in topsoil.There is an contrary action in subsoil.The soil three phases were far from the optimal structure point because of various soil compaction.(3)Heavy machinery operation could increased the available phosphorus content significantly

especially after subsoiling in topsoil

and the improvement scope was 20.07%~380.91%.The concentration of soil available potassium both heightened after heavy and medium machinery operation

with different increase scope: 10.04%~20.61% and 17.05%~27.52% respectively.Soil available nitrogen was not sensitive to machinery operation

T test showed that the differences were insignificant except for medium machinery in subsoil.