Abstract:

The aim of this study was to devise a planting system conducive to maintaining good physical and chemical properties of farmland soil in the arid area of Northwest China. Therefore， a field experiment was conducted to determine the effects of different planting patterns of flax （Linum usitatissimum） alone or with other crops， wheat （W， Triticum aestivum） and potato （P， Solanum tuberosum）， on soil properties. The experimental treatments consisted of 100% flax， 50% flax （Ⅰ）， 50% flax （Ⅱ） and 25% flax， with a fallow treatment as the control. Under the four flax planting frequencies， 100% flax （Cont F） consisted of flax only， 50% flax （Ⅰ） consisted of flax alongside W and P， planted with the following pattern： WFPF， FPFW， PFWF， FWFP； 50% flax （Ⅱ） consisted of flax alongside W and P planted with the following pattern： FWPF， WPFF， PFFW， FFWP； and 25% flax consisted of flax alongside W and P planted with the following pattern： WPWF， PWFW， WFWP， FWPW. The stability of farmland soil aggregates and the distribution of nitrogen under these 13 crop rotation systems were determined. We detected very significant negative correlations between soil aggregate mean weight diameter （MWD） and geometric mean diameter （GMD）， fractal dimension （D）， and percentage of aggregate destruction （PAD）. There were significant positive correlations between MWD and NH₄⁺-N content in the 0.5-1.0 mm particle size fraction and NO₃^--N content in the >2 mm particle size fraction. The nitrate ammonium nitrogen content increased with increasing soil aggregate stability. The planting frequency of 50% flax （Ⅰ） and potato stubble significantly increased the amount of soil aggregates in the >0.25 mm size class and macroaggregate MWD and GMD， and significantly reduced soil D， PAD， and soil erodibility. The FWFP treatment increased the amount of soil aggregates in the 0.25-2.00 mm size class， significantly increased soil aggregate MWD and GMD and erosion resistance， reduced soil D and PAD， and made the soil aggregate structure more stable. These results show that the FWFP rotation can significantly improve soil water content and soil stability and increase the contents of soil aggregates and their stability. This information is important for the sustainable development of flax cultivation in Northern China.

Key words: flax, soil aggregate, aggregate stability, nitrogen distribution