Effects Of Planting Alfalfa On Soil Quality In The Semi-arid Loess Plateau. China

We select four typical slope situation in north mountainous country area , namely upper land, middle land, foot land, flat, and we select two land use : alfalfa and crop .there are 10 samples in alfalfa land and 10 samples in crop land, for a purpose of restoration and construction on the Loess Plateau .The results as shown follows:In my study, crop species respective is : flax ,field pea ,spring wheat, potato, millet straw and sorghum. WUE of spring wheat is largest among these crops, and the second largest is sorghum. The smallest is field pea .If we compute WUE depend on 0-100cm,the result as shown follow: WUE of spring wheat is 23.2kgha^-1mm^-1,sorghum is 21.5 kgha^-1mm^-1,field pea is 5.6 kgha^-1mm^-1; If we compute WUE depend on 0-200cm,the result as shown follow: WUE of spring wheat is 25.2 kgha^-1mm^-1,sorghum is 20.0 kgha^-1mm^-1,field pea is 6.02 kgha^-1mm^-1; There is no disciplinarian between alfalfa land and crop land in various slope situation, the largest yield is sorghum, namely is 4144 kgha^-1, the second largest yield is spring wheat, namely is 3268 kgha^-1, the smallest yield is field pea, namely is 660.4kgha^-1, the deep_root crop and anti-arid crop can show its superiority in drought year.WUE of 4yr-alfalfa is especially larger than other crop , except spring wheat and sorghum ,and there are strong different in various slope situation. The rule of WUE is : foot land > flat > upper land > middle land. If we compute WUE depend on 0-500cm,the result is smaller than the result of WUE depend on 0-200cm, the main reason is that 4yr-alfalfa can absorb water deep into 2 meter.SMN of alfalfa is smaller than crop by 42.5%, but total nitrogen larger than crop by 26.7%,the main reason is that planting alfalfa can increase soil nitrogen pool .because crop is fertilized, NO₃^--N content of crop is 4.67 multiple for alfalfa., and NH4⁺-N content is not infected by land use and slope situation.We can get the conclusion: in various slope situation , the foot land is the best situation ,nutrient and moisture have been enriched in foot land. SOC , LFOC, MBC, TN, NO₃^--N, TP and AP have all been enriched in foot land. Since planting alfalfa, TN increased by 26.7%, LFOC increased by 50%, SMBC increased 41%.soil quality have been boost; soil water content of alfalfa is smaller than crop land ,the main reason is that alfalfa can absorb deep water. A good method is rotate shallow-root crop which can reform soil water.