Determining The Upper Limit Of Phosphorus Content In Livestock And Poultry Excrement Used As Fertilizers

In recent years, domestic livestock and poultry cultivation has developed rapidly in China and got a great achievement that attracts worldwide attention. However, the management of excrement has been neglected in the process of livestock and poultry development. The massive livestock and poultry sewage has not been reasonably treated and utilized, which caused the serious pollution to the environment. Livestock and poultry excrement pollution has been the main factor puzzles many big to media-sized cities, as well as sustainable development in national agriculture. At present the annual production of livestock and poultry excrement is much higher than that of industrial waste, and becomes an important source of non-point pollution in countryside. Application of livestock and poultry excrement in farmland based on the amount of nitrogen by soil test may have left excessive accumulation of phosphorus in the soil and thus caused environmental problem.This paper elaborated the general situation of development and the characteristic of the livestock and poultry breeding in our country, the production and nutrient content of livestock and poultry excrement; It summarized the maim harm of excrement from livestock and poultry breeding, including water, soil and air contamination , as well as occupancy and pollution of farmland in our country; Furthermore, in this paper we introduced the forms and transformation, fixation and release of phosphorus in the soil, phosphorus migration in the soil environment, the evaluating index of soil phosphorus loss potential, and international research tendency on the mechanism of phosphorus loss.The experimental designs in this paper include: 1) There types of soil, that is, red soil, yellow fluvo-aquic soil and yellow-brown soil, were used for the expriment. Chicken manure, cow dung and pig excrement were applied at dosages of 0, 30, 40, 60, 90, 130, 180, 240, 310 mg/kg P to the soils. After alternation of wet and dry cultivation, the contents of rapid available phosphorus (Olsen-P), total phosphorus and CaCl₂-P in soil were determined. The change-Point of phosphorus leaking was studied based on the relation between CaCl₂-P content and rapid available phosphorus (Olsen-P) content. The critical index of upper limit of phosphorus was determined for safe manure application in different soils. 2)Simulating cultivation with soil column was carried out to study phosphorus migration patterns in soil treated with manure. The same dosage of manure as used in the first experiment were used. After wet and dry cultivation, the soils were dried and Olsen-P and total phosphorus contents in soil samples were determined from layer 0⁵, 5¹0 and 10²0 cm. 3)During the process of simulated soil column cultivation, leakage fluid was sampled by stages and total phosphorus content of each sample was determined, in order to study the influence of manure application on soil phosphorus leakage. 4)Pot experiment was carried out to study the effect of plant growth on reducing the manure leakage. Calatheazebrina and Nageia were planted in there types of soils amended with 130, 180, 240 and 310 mg/kg P individually. Those treated with 130 mg/kg P with no plant were taken as controls for each soil type. Leakage fluid from each pot was sampled 3 times to determine total phosphorus content. The main results obtained were as follows:1) Soil available P (Olsen-P) and CaCl₂-P increased gradually when raising the amount of manure applied. The increase of Soil CaCl₂-P content was positively related to that of Olsen-P. This increase would reach to a so called Change-point, which was the threshold (upper limit) of soil phosphorous leaking loss. Different manures had different thresholds of phosphorous (Olsen-P) loss in various soils. For chicken feces this value varied from 61.02 to 64.08mg/kg, for cow dung 23.46-40.12mg/kg, and for pig excrement 66.4-71.25mg/kg. The average change-point about chicken feces and pig excrement were around 61.02-71.25mg/kg.But the average change-point about cow dung was very low. 2) With the increase in depth, available phosphorous decreased gradually in flushed soils. It increased in the layer of 10-20 cm but not significantly. Soil available P could not be readily transferred by water. For example, only small portion of P was transferred further than 20 cm by one year precipitation. Application of different types of manure increased soil available P dramatically in the layer of 0-5 cm. In yellow-brown soil >in yellow fluvo-aquic soil> in red soil. When deeper than 5 cm, there was no big difference among the manures or soils.3) When pig manure was applied, total P in leakage loss was significantly higher in red soil than in yellow fluvo-aquic soil, which showed much higher affinity to P in pig manure. On the contrary, red soil had higher affinity to P in cow dung.4) After manure treatment, P contents in soil leakage from the pots with plants were much lower than those of the control, namely without plants. Plants played an important role in fixing P. Vegetation type differed in their abilities in absorption and fixation of phosphorous.