Effect Of Alfaifa Planting Years On The Productivity And Soil Quality

The test carried out from the trial of long term located fertilization different planting years of Alfalfa in Helan mountain, studied different growth years of alfalfa forage yield and agronomic characteristics, photosynthetic characteristics, nutritional quality and soil physicochemical properties, biological properties under water and fertilizer conditions, in order to explore the mechanism of degradation of Alfalfa, to provide technical support and determination of the length and high yield cultivation for our area under irrigation condition. The main results are as follows:1. After4years raw alfalfa has the highest annual production, then began to be markedly decrease. Correlation analysis indicate that, Alfalfa forage yield and plant height, number of unit area trees has the extremely significant correlation, and significantly correlated with the number of branches per plant.2. Each planting years alfalfa leaf photosynthetic rate, transpiration rate, stomatal conductance, leaf temperature with the passage of the seasons overall downward trend, intercellular CO2concentration, photosynthetic active radiation was first decreased and then increased, leaf temperature decreased.4year alfalfa average photosynthetic was the highest, and the strongest production capacity. Correlation analysis indicate that, the biggest influence factor of photosynthetic rate is photosynthetically active radiation, followed is stomatal transpiration rate; the most influential factor of transpiration rate is photosynthetically active radiation and stomatal conductance, followed is leaf temperature.3. Alfalfa planting2years its crude protein, crude fat, crude ash, digestibility were the highest,6year alfalfa crude fiber content was the highest. Correlation analysis indicate that, Crude protein and crude fiber, nitrogen free extract showed a negative correlation, and crude fat, crude ash, digestibility were positively correlated; Crude fiber and crude fat, crude ash, digestibility significantly negative correlation.4. The years alfalfa soil water content as the season progresses goes on irregular distribution; with the increase of soil depth, a trend of first increase and then decrease,20～40cm soil water content in the highest.6year alfalfa soil bulk density, soil porosity minimum, saturated water content was the highest,3year alfalfa with just the opposite.5. With the extended length of alfalfa, the soil organic matter, total nitrogen, alkali solution nitrogen content were significantly increased, the content of available phosphorus and available potassium decreased. With the increase of soil depth, soil nutrient all showed a trend of decline.6.4year alfalfa to microbial total maximum, minimum6years. The planting alfalfa soil microbial flora in the bacteria accounted for more than60%of the total, is the main soil microorganism, followed by actinomycetes, fungi the least number. Increase the proportion of soil bacteria and fungi with the planting years increasing, actinomyces decreased than column.7. The TOPSIS method to get the comprehensive analysis,4years for the best years of planting alfalfa, more than4years, the decrease of the indicators, grassland deterioration.