Vegetables production is an important component of suburb agriculture. Therefore, it plays important roles in the sustainable development of suburb agriculture and economy, and stability of society. In 1995, the cultivation area of vegetables was 9.5 million ha, increasing by over two times as compared with 1985 in China. In 1995, total output of vegetables was 25.73 million t, increasing by 106.3% over 1985; the average amount of vegetables per capita was 217 kg and 120 kg in the corresponding period. In 2001, the cultivation area of vegetables was 16 million ha, increasing 0.86 million ha as compared with the last year, and the total output of vegetables was 30 million t, the average amount of vegetables per capita was 230 kg/year (estimated by1.3 billion population of China), which are three times as the average level of the world. However, vegetable products with low quality not only affect human life quality and human health, but also affect output of vegetable products of China. On the other hand, it will further reduce the vegetable quality because of environmental pollution due to improper use of fertilizers and pesticides. Thus, it is important to reduce environmental pollution in the vegetable production and meet the consumer’s and output’s demands for sensory, nutritional and safety quality of vegetable.
Vegetable crops have higher nutritional requirement and economic benefits from fertilization than those of other crops. Thus, in order to get higher yield of vegetables, producers may apply chemical fertilizer and organic manure excessively in many cases. According to an investigation in Yan’an of China in 2003, one problems involved in fertilization is excessive use of N and P fertilizers. The long-term excessive use of chemical fertilizer and organic manure have resulted in nitrate and P accumulation in protected vegetable fields. The results obtained from Nanjing showed that the application ratios of N, P₂O₅, K₂O in Chinese cabbage and tomato were 1: 0.39: 0.25 and 1: 0.34: 0.17, respectively; whereas proper ratios suggested were 1: 0.55: 1.25 and 1: 0.39: 1.20, respectively. K deficiency was occurred in most of vegetable soils in China. P was accumulation in most vegetable soils because of long-term application of P fertilizers. Similar results were obtained in Hangzhou. Of 60 soils distributed in new and old vegetable garden in Hangzhou suburb, most of the soils were sufficient in P and 93% of the soils were deficient in K. Recently, we determined the nutrient contents of 154 vegetable soils collected from vegetable fields of the suburb of Hangzhou. The results showed that P contents in 154 soils were higher than that of critical level of ASI, which their contents ranged from 71.6-428.06mg/L, and its average content was 202.6mg/L. Soil K contents varied from 22.8 mg/L to 177.3 mg/L, and its average was 58.5 mg/L only. According to critical level of ASI for K is 78 mg/L, K deficient soils accounted for above 83.8%. It is very common for P accumulation and K deficiency in vegetable soils. Thus, over application of N and P fertilizers induced N and P accumulation in vegetable soils not only resulted in saline accumulation and nutrient imbalance, but also reduces yield and quality of vegetables and increases the risk of P and nitrate release to and groundwater.
People have paid widespread attention to pesticide contamination of vegetables. However, Heavy metal pollution to soils and vegetables is getting a serious question, which gains a special interest at present. There is considerable evidence in the literature to suggest that vegetable soils and vegetables have been subject to heavy metal contamination to a great degree that affects human health. Vegetables are the staple foods in China. Therefore more attention should be paid to minimizing metal contamination in the processes of vegetable production.
The major routes of heavy metal inputs to agricultural soils include atmospheric deposition, sewage sludge, animal manures, agro-chemicals and inorganic fertilizers. Losses occur through off take in crops or livestock products, leaching and soil erosion. Whilst some researchers have considered in some detail metal inputs to soils via sewage sludge, inorganic fertilizers and atmospheric deposition, there has to date been little information available on heavy metal pollution to soils and vegetables via animal manures. In the process of animal production, some micro-nutrients have been used as additives in the animal diets. Diets of poultry and livestock include metals and metalloids (As, Co, Cu, Fe, Mn, Se, Zn) to prevent diseases, improve weight gains, and increase egg production. However, in pig farming, the amount of copper eliminated through the animal faeces corresponds to 72-80% of the amount ingested, whereas for zinc this can be as high as 92-96%. It is estimated that the amount of micronutrients as additives reached 150,000 t, however, about 100,000 t micronutrients did not absorbed and released to environment in the form of faeces. In a study by Nicholson, 183 livestock feeds and animal manures samples were collected from commercial farms in England and Wales and analyzed to determine their heavy metal. It was found that Zinc and copper concentrations ranged from 150-2,920 mg Zn/kg DM and 18-217 mg Cu/kg DM in pig feed, depending on the age of the pigs. In poultry feeds, concentrations ranged from 28-4,030 mg Zn/kg DM and 5-234 mg Cu/kg DM, with laying hen feeds generally having higher heavy metal contents than broiler feeds. Pig manures typically contained c. 500 mg Zn/kg DM and c. 360 mg Cu/kg DM, reflecting metal concentrations in the feeds. Typical concentrations in poultry manures were c. 400 mg Zn/kg DM and c. 80 mg Cu/kg DM, and in cattle manures C. 180 mg Zn/kg DM and c. 50 mg Cu/kg DM. Mcbride and Spiers (2001) reported that pig manures contained 500-1,000 mg Cu/kg DM. Other study has also reported that mean total Cu, Ni, Zn, and As concentrations in poultry litter (PL) were 479, 11, 373, and 16 mg/kg, respectively. An inventory of heavy metal inputs to agricultural soils in England and Wales in 2000 was made by Nicholson. It was found that livestock manures and sewage sludge were important sources inputs to agricultural soils, responsible for an estimated 37-40 and 8-17% of total Zn and Cu inputs, respectively. Some authors reported that heavy metals can accumulate in agricultural soils due to the application of liquid and solid manure in some cases. However, the accumulation of heavy metals in soils must increase the potential risk of groundwater contamination via leaching. It is generally accepted that soils are subject to heavy metal pollution which is toxic to plant when available Cu and Zn contents reach 100-200 and 100 mg/kg, respectively. If As has been used as additive for 15 years in a farm of 100,000 chickens, it will result in As content of plant foods cultivated in the soils near the farm higher than the critical level of national standard (Kong Yuan and Han Lujia, 2002). Therefore, overapplication and improper use of organic manures has been becoming an important factor affecting safety quality of vegetables and environment security, it is urgent to investigate the ecological and environmental security of application of organic manures in vegetable soils. However, there is a little information available in the literature on the effect of application of organic manure on manure-borne heavy metal transformation, accumulation, and transportation in vegetable soils, and the risk of heavy metal contamination of vegetable. There are also relatively few studies of potassium effects on both heavy metal transfer and accumulation in vegetable soil and uptake of vegetable crops under potassium deficiency in the vegetable soils.
The overall objective of the study is to study the beneficial effects and risks of organic manure application in vegetable soils. Specific objectives of the present study are: 1) to investigate situation of animal manure application in vegetable soils in Hangzhou; 2) to evaluation the nutrient and heavy metal contents of typical animal manures in Hangzhou; 3) to monitor the heavy metal content in the soils and vegetables in Hangzhou; 4) to study the influence of animal manure on nitrogen, phosphorus and heavy metal transformation, accumulation and leach ability in a sandy loam vegetable soil after manure application; 5) to investigate the uptake and accumulation of nitrate and heavy metal accumulation in vegetables from manure amended vegetable soil and to quantify the amount of nitrate, phosphorus, and heavy metals in leachates from the soils, and its effect of potassium; 6) to establish sound strategies of animal manure application in order to protect ecological and environmental security and produce nutritional and safety vegetables.