Effects Of Long-term Fertilization Crop Yields And Soil Quality In A Semi-arid Area Of Northwest China

Improving and maintaining soil quality is of paramount importance to meet the food demands of increasing population in China. Fertilization is one of the soil and crop management practices which exert a considerable influence on soil quality. However, many previous studies demonstrated inconsistent results that the effects of fertilization on crop yields and soil quality. Moreover, such study has been conducted rarely on loess soils. Crop yields, total soil organic matter (SOM) and its sensitive fractions, and soil physical, chemical and biological properties have been proposed as indicators of soil quality. Therefore, we investigate the responses of fertilization to soil organic matter and its physically-separated fractions, and soil physical, chemical and biological properties through the long-term field experiment at a site of semiarid Loess Plateau, which is initiated in1981. Finally, principal component analysis and cluster analysis were used to evaluate soil quality in different fertilization treatments. The results were shown as following:1. Except for1982, application of fertilizers (N, NP and NPK) or manure markedly increased wheat yield compared to nil-fertilization, moreover, combination of manure and chemical fertilizers increased wheat grain production more than did manure or chemical fertilizers alone. Chemical fertilizations and manuring significantly enhanced wheat root biomass (0-20cm) and root density (0-60cm) on the flowering stage, and wheat root biomass was closely related to wheat yield. Wheat yield of all treatments and precipitation in wheat growing seasons gradually declined with the extension of the experiment continuous time, moreover, excluding nil-fertilization and alone manure treatments, there were significantly positive relationships between yields of the others treatments and precipitation in wheat growing seasons.2. Manuring significantly reduced soil density (0-20cm) and increased0.5-0.25mm water-stable aggregates concentration as compared with no manuring treatment. Combining application of chemical fertilizers (NP and NPK) markedly improved0.5-0.25mm water-stable aggregates concentration, but it had no notable effect on soil density compared with nil-fertilization. Organic C and N concentrations of all water-stable-aggregate fractions were generally affected by both organic and mineral fertilizations and magnitudes of increases were greater for1-0.5and0.5-0.25mm water-stable-aggregate fractions than for the other fractions. Soil OC, N concentrations and C:N ratios in the larger size water-stable aggregates were significantly higher than those in smaller size water stable aggregates.3. Application of nitrogen and farmyard manure significantly elevated soil (0-20cm) NO-3-N concentration in soil profile (0-100cm) compared with nil-fertilization, by contrast, combination of nitrogen fertilizer and farmyard manure (MN), phosphate (NP) or phosphate and potassium fertilizers (NPK) significantly reduced soil profile NO-3-N concentration compared with nitrogen fertilizer alone (N). Farmyard manure and phosphate fertilizer use significantly improved0-20cm and20-40cm soil Olsen-P concentration, long-term application of farmyard manure and nitrogen fertilizer significantly decreased soil PH compared with nil-fertilization. Simultaneity, long-term application of farmyard manure significantly increased soil available iron, manganese, copper and zinc concentrations in bulk soil compared with nil-fertilization.4. Application of farmyard manure and chemical fertilizers significantly increased soil microbial biomass carbon, biomass nitrogen concentrations and soil alkaline phosphatase,β-glucosidase, urease and acidic phosphatase activities compared with nil-fertilization. In different wheat growth stages, alkaline phosphatase, β-glucosidase, urease and acidic phosphatase activities decreased in the order of flowering stage>jointing stage>harvesting stage.5. Farmyard manure and chemical fertilizers (N, NP and NPK) significantly increased total soil OC and N concentrations compared with nil-fertilization. Compared with nil-fertilization, long-term application of manure significantly increased soil light OC (Density<1.8g/cm3) and coarse OC (Size>0.05mm) concentrations, while long-term application of chemical fertilizers significantly increased soil light OC and mineral-associated OC (Density>1.8g/cm3) concentrations, and its effect on coarse OC (Size>0.05mm) concentration in bulk soil was not observed. Light OC was more sensitive but smaller reservoir than coarse OC in bulk soil.6. Wheat yield correlated positively with total soil OC, N, phosphorus, soil coarse OC(Size>0.05mm), soil light OC(Density<1.8g/cm3), microbial biomass carbon concentrations and enzyme activities, moreover, the relationship between wheat yield and soil light OC concentration was stronger than that of wheat yield and soil coarse OC (Size>0.05mm) concentration on wheat harvesting stage. Wheat yield and root biomass correlated positively with soil average mass diameter. Wheat average root length density negatively correlated to soil moisture content on wheat flowering stage.7. With the extension of the experiment continuous time, soil OC and total nitrogen concentrations markedly increased in all fertilization treatments cmpared with the initial values of the experiment beginning, and the increased magnitude of soil OC and total nitrogen concentrations in combining chemical fertilizers with farmyard manure treatments were higher than the increased amount by either farmyard manure or chemical fertilizers alone. Without phosphorus input, Olsen-P concentration decreased in bulk soil, by contrast, soil Olsen-P concentration significantly increased if phosphorus fertilizer and manure were applied with the extension of the experiment continuous time.In general, long-term application of chemical fertilizers (NP and NPK) and farmyard manure significantly increased crop yields, enhanced total soil OC, labile OC and soil nutrient concentrations, increased soil microbial biomass activities compared to nil-fertilization. Moreover, application of chemical fertilizers (NP and NPK) or farmyard manure significantly increased soil OC, total nitrogen and Olsen-P concentrations compared to the initial values of the experiment beginning. Therefore, long-term application of chemical fertilizers (NP and NPK) and farmyard manure significantly improved soil quality and combination of manure and chemical fertilizers more efficient than by either farmyard manure or chemical fertilizers alone. Due to the changes of climate, precipitation gradually decreased in wheat growth seasons, which limited wheat yield and resulted in wheat yield declined gradually with time.