Phosphorus Forms Characteristics Of Shanxi Typical Farmland Soils And Evaluation Of Agronomic And Environmental Significance After Fertilization

Since the second soil survey in China from 1979 to 1985,after 40 years,we are not clearly about the Shanxi typical farmland fertilizer status,P accumulation characteristics,P mineralization after organic fertilizer application and the risk of non-point source P loss.So this study collected Shanxi 28 typical farmland soil samples,by testing soil fertilizer,P forms and the bioavailability of P after applying organic manure,clarifying the mechanism of different organic fertilizers on the bioavailability of P in Shanxi typical farmland,revealing the regulation of soil agronomy and environmental P forms,establishing a model of agronomy and environmental P,and adopting the "change-point" predicts the loss of environmental P threshold.The research results are as follows:(1)Shanxi typical farmland soils’ basic fertility and P status are as follows: available P is in the range of 1.06~78.6mg/kg,total P 0.12~1.83g/kg,the coefficient of variation is 102% and 89%,respectively.Other fertility indicators are as follows: total potassium 26.68~371.896 mg/kg(coefficient of variation:36%),available potassium 26.68~371.896mg/kg(coefficient of variation: 45%),total nitrogen26.68~371.896mg/kg(coefficient of variation: 47%),alkaline nitrogen 3.5~72.33mg/kg(coefficient of variation: 50%),organic matter 4.2~30.5 mg/kg(coefficient of variation: 49%),p H 7.31~8.64(coefficient of variation: 4%).The fertility indicators are compared with the second national soil survey,the majority of organic matter content is at a medium level,accounting for 71.43% of the total samples;total nitrogen and alkali nitrogen are at a low level(at the fifth and sixth levels);available potassium is at a medium to high level;p H is at a middle and low level,low level is main;the available P content is unevenly distributed everywhere,with high,medium and low levels,mainly at medium levels.The total amount of inorganic P is in the range of 141.12~823.44mg/kg,and the content of each component is:Ca-P(115.23~747.52mg/kg)> Al-P(1.75~78.87mg/kg)> O-P(2.61~104.9mg/kg)> Fe-P(1.42~49.82mg/kg).And the invalid state Ca10-P has the largest proportion,reaching 80%~90.7%.According to the correlation analysis between the different inorganic P forms and Olsen-P,the results show: Ca2-P,Ca8-P,Al-P and Olsen-P were extremely significantly positively correlated,the correlation coefficients are 0.636**(P=0.000),0.594**(P=0.001),and 0.547**(P=0.003),respectivel,Fe-P and Olsen-P reaching significant correlation levels(r=0.436*,P=0.021),O-P and Ca10-P were not significantly correlated with available P(r values were:-0.015,-0.018;P values were: 0.559,0.527,respectively).(2)A pot experiment was conducted to study the P mineralization process in different incubation periods(2 weeks,4 weeks,8 weeks,16 weeks)by applying liquid chicken manure,liquid swine,liquid dairy manure and no fertilization in Shanxi typical farmland soils.The results show,at the same P level,compared with other treatments(liquid chicken manure,liquid swine,liquid dairy manure)ryegrass fresh weight,ryegrass dry weight and ryegrass P absorption were the highest,followed by liquid chicken manure and liquid dairy manure(except for individual).Correlation analysis between the amount of P absorbed by ryegrass and Mehlich-3 P,Olsen-P showed that,incubation 2 week,the correlation between the P uptake of ryegrass and Mehlich-3 P was best r=0.240**(P=0.011),and the correlation between the P uptake of ryegrass and Olsen-P at the 4th week was the best r=0.286**(P=0.002).(3)The effects of different fertilization treatments on soil agronomic phosphorus(Mehlich-3 P,Olsen P)and environmental phosphorus(water extracted phosphorus,CaCl2-P)in different soil types were as follows: the contents of Olsen-P,Mehlich-3 P,Water extractable P and CaCl2-P in the fluvo-aquic soil are much higher than other soil types;in the four periods of incubation,the increased content of Olsen-P,Mehlich-3 P,Water extractable P and CaCl2-P was the highest in the treatment of liquid swine compared with other fertilization treatments.After the soil culture was completed(16 weeks),the soil P holding saturation(DPS)analysis by different fertilization treatments showed that the order of influence of each treatment on DPS was: liquid swine > liquid chicken manure > liquid dairy manure > no fertilization,visibly,the holding ability of liquid swine is stronger than liquid chicken manure,liquid dairy manure and no fertilization treatment.The correlation analysis between agronomy and environmental P in four incubation periods showed that except for the 2th week,CaCl2-P had no significant correlation with water extractable P,and the other indexes reached a extremely significant level in the four incubation periods.This paper analyzes the relationship between agronomy P and environmental phosphorus,showing that environmental P(CaCl2-P and Water extractable P)and agronomy P(Olsen-P,Mehlich-3P)and soil P holding saturation DPSCa+Mg both have a linear relationship,and the correlation coefficient between CaCl2-P and Olsen-P,Mehlich-3P,DPS(Ca+Mg)is greater than Water extractable P.Therefore,CaCl2-P can be used as a threshold for monitoring the risk of soil environmental loss in Shanxi typical farmland,when Olsen-P>21.43mg/kg(CaCl2-P is 0.55 mg/kg)and Mehlich-3P>92.29mg/kg(CaCl2-P is 1.30mg/kg);DPS>16.67%(CaCl2-P is 1.15mg/kg),therefore,the above threshold value is initially set as the threshold value of P loss in Shanxi typical farmland soil.