Responses Of Wheat Yield,Quality And Heavy Metals To Longterm Straw Returning And Manure Compost Application

Crop straw and livestock manure are the most important organic fertilizer that contains organic nutrients such as amino acids, nucleic acids, sugars, and vitamins, but it is also a valuable source of organic matter, nitrogen, phosphorus, potassium, and some micronutrients.The North China Plain is one of the world’s most important agricultural regions, where 35 million ha of croplands produce about 61%, 39% of the wheat and maize used in China, as well as supplying 25%, 45%, and 33% of the meat, eggs, and milk, respectively, used in the country. Therefore, the production of livestock and poultry manure amounted to almost 4.8 billion tons in 2010, which was 25% of the total in China. However, over the past three decades, due to the rapid development of the economy, extra labor demands, and high cost inefficiencies, the traditional cropping practice with organic manure application has almost disappeared, where chemical fertilizers are now used widely in crop production as the main sources of crop nutrients. Thus, the input of nutrients with organic fertilizer into farmland had gradually decreased. Obviously, this nutrient imbalance is a growing threat to food security on the North China Plain, where most of the regions are dependent on agriculture. Therefore, using different cultivation methods in the crop production area, especially straw returning and compost manure are the efficient options to resolve the agriculture and environment problems on the North China Plain.A long-term experiment was established in 2005, and this study based on an two-year long stationary field experiment in a typical cereal crop production area of the North China Plain to investigate the effects of different amounts of straw returning and compost manure application rates on wheat yield and the macro-/micro-nutrients and heavy metals contents of soil and wheat, as well as on nutrient balance and safety in the soil-plant system.The main objective of this study was to evaluate the effects of different cultivation methods, and provide theoretical supports and practical experience for high quality, high efficiency, high yielding, low cost and minimum impacts on environment. The main results were as follows:(1) Based on a location-fixed field experiment was conducted to investigate the effects of different amounts of straw returning on the macro-/micro-nutrients and heavy metals contents of soil. Results showed that 50% and 100% straw returning significantly increased the soil total N, the available P, K, Fe, and Zn concentrations, whereas the available Cu decreased, and the available Mn concentrations in soil exhibited different trends. Compared with the 100% straw returning, the 50% straw returning treatments increased the soil total N by 10.4% and 5.2%, soil available P by 20.8% and 7.5%, soil available K by 3.6% and 3.3%, soil available Fe by 1.9% and 3.4%, and soil available Zn by 24.9% and 17.8%, respectively, over the two years.We also compared the mean concentrations of Cd,Cr and Pb with the thresholds for elements in the natural background soil in China, where all of the results obtained for heavy metals were much lower than the corresponding threshold values, which indicates that the concentrations of the heavy metals were within the safe levels, so the soils in the present study can be considered “clean.”(2) A field experiment was conducted to investigate the effects of different amounts of straw returning on wheat yield and the macro-/micro-nutrients and heavy metals contents of wheat. Results showed that 50% and 100% straw returning increased the grain yield and biomass of wheat. Compared with the control, 50% and 100% straw returning treatments increased the grain yield by 5.4% and 5.7%, and biomass by 4.9% and 5.9%, respectively, over the two years.Compared with the 100% straw returning, the treatment of 50% straw returning increased the grain N concentration by 4.2% and 4.5%,and the grain P concentration by 7.8% and 4%, respectively, over the two years. The K concentration in grain tended to increase with the 50% straw returning treatments, i.e., 2% and 10.7% increases compared with the 100% straw returning treatments during both years, respectively. Compared with the control, the treatment of 50% straw returning increased the straw Fe concentration by 12.6% and 26.9%, and increased the straw Zn concentration by 16.9% and 14.5%, respectively, over the two years. Compared with the control, 100% straw returning treatments increased the straw Fe concentration by 15.9% and 40.4%, and increased the straw Zn concentration by 15.1% and 18%, respectively, over the two years.Compared with the100% straw returning, the 50% straw returning treatments decreased the grain Fe by 0.6% and 10.3%, grain Zn by 11.2% and 9.2%, grain Cu by 9.1% and 4.7%, and grain Mn by 7.5% and 4.1%, respectively, over the two years.The average Cr concentrations in wheat straw and grain ranged from 0.1 to 0.17 mg kg-1 and 0.04 to 0.09 mg kg-1 over the two years, respectively. The concentrations of Cd and Pb in wheat straw and grain were too low to be determined.The Cr concentrations in the edible parts of wheat, which was still much lower than the limit, which indicates that the concentrations of the heavy metals were within the safe levels.(3) Based on a stationary field experiment was conducted to determine the effects of compost manure application rates on the macro-/micro-nutrients and heavy metals contents of soil, as well as on nutrient balance and safety in the soil-plant system. Results showed that the application of compost did not affect the soil total N at low rates, whereas it significantly enhanced the total N at high rates. Compared with the control, the total N concentration increased significantly by 17% and 10% over the two years, respectively. The soil available P concentration did not increase significantly with the compost inclusion rate. At higher compost application rates(22500 and 30000 kg ha–1), the soil available K concentration increased by 35% and 43% respectively, over the two years,compared with the control. The application of compost decreased the concentration of soil available Cu, whereas the concentrations of Fe, Zn, and Mn increased. At higher compost application rates(22500 and 30000 kg ha–1), the soil available Fe concentration increased by 26% and 11%, and the soil available Zn concentration increased by 42% and 43% respectively, over the two years, compared with the control.Under different compost application rates, the soil available Mn concentration increased by 2% and 11% respectively, over the two years, compared with the control. The average available Cu concentrations in the soil under compost application over the two years, which were 14% and 11% lower than that with the control, respectively. Under different compost application rates, the concentration of Cd in the soil ranged from 0.09 to 0.18 mg kg-1, the soil Cr ranged from 51.6 to 56.8 mg kg-1, the soil Pb ranged from 3.2 to 7.1 mg kg-1 over the two years, respectively.We also compared the mean concentrations of Cd,Cr and Pb with the thresholds for elements in the natural background soil in China, where all of the results obtained for heavy metals were much lower than the corresponding threshold values, which indicates that the concentrations of the heavy metals were within the safe levels. The balances of the macro-and micro-nutrients indicated that the removal of nutrients by wheat was compensated for by the addition of compost, whereas the level of N decreased without the application of compost.(4) Based on a location-fixed field experiment in a typical cereal crop production area of the North China Plain to investigate the effects of compost manure application rates on wheat yield and the macro-/micro-nutrients and heavy metals contents of wheat, as well as on health risks related to micronutrients and heavy metals in wheat grain. Results showed that the grain yield and biomass of winter wheat did not increase significantly with the compost inclusion rate.However, the straw N concentration decreased by 9% and 18%, and grain N concentration decreased by 16% and 12%, respectively, over the two years. At lower compost application rates(7500kg ha–1), where the maximum level of the grain P was 5.0 g kg–1and 4.7 g kg–1, which was 40% and 13% higher than that with the control. Compared with the control, the application of manure compost significantly increased the K concentration in wheat grain by17% in the second year. Compared with the corresponding controls, the compost treatment increased the Fe concentrations in wheat straw and grain by 46% and 53%, respectively, over the two years, as well as enhancing the Zn concentration by 12% in the second year. By contrast, the application of compost decreased the Mn concentration in wheat straw and grain by 9% and 18%, respectively, and reduced the grain Cu concentration by 14% over the two-year period. The concentrations of Cd and Pb in wheat straw and grain were too low to be determined. The average Cr concentrations in wheat grain ranged from 0.07 to 0.68 mg kg-1 over the two years.The Cr concentrations in the edible parts of wheat, which was still much lower than the limit,which indicates that the concentrations of the heavy metals were within the safe levels. The daily intake levels of micronutrients via the consumption of wheat grain were still lower than the recommended levels when sheep manure compost was applied, except for that of Mn.