| Agricultural returning to farmland is one of the preferred ways to deal with the wastewater of large-scale livestock and poultry farms.As the most important cash crop in Hainan province,rubber occupies for a significant proportion of tropical plants.Considering the potential impact of antibiotics and heavy metals in biogas slurry in food chain,the development of "hog-biogas liquid-rubber" ecological circulation agriculture model with biogas liquid as a link has a broad prospect in Hainan.However,the model of"hog-biogas liquid-rubber" encountered a major problem of returning livestock and poultry waste to the field,that is,the input of a large amount of biogas liquid led to an increase in the residual amount in the soil,which could easily lead to the degradation of soil structure and ecological function.While affecting the normal growth of rubber trees,it also increased the risk of pollution of ecological environment.Therefore,the study on the relationship between biogas liquid and appropriate amount of consumption of ecosystem of rubber tree and response relationship can not only make fill up for the gaps in related research,but also provide an important theoretical basis for agricultural practical production.In order to this study the effects of different application rates of biogas liquid on the growth and soil physical/chemical properties and fertility of rubber trees,through the combination of indoor pot experiment and field experiment,the rubber seedlings,10 years old and 30 years old rubber plantations were selected as experimental objects,and seven different application gradients of biogas liquid were set up.The annual fertilizer amount in per mu is 15 m3?T1??30 m3?T2??45 m3?T3??60 m3?T4??75 m3?T5?,90 m3?T6?and blank experiment?TO?.The effects of different application rates of biogas liquid on the growth and soil physical/chemical properties and fertility of rubber trees were studied.To investigate the optimal capacity of biogas liquid absorption,a soil quality index evaluation system was established to select the candidate factor parameter sets which containing most of soil quality information.Meanwhile,based on land fertilizer requirement and quality condition,the number of pig head and the area of rubber forest in large-scale pig farm were reasonably estimated and optimized.The main findings are as follows:1.Effects of biogas liquor application on rubber seedlings growth characteristics results showed that:Proper biogas liquid application could increase rubber seedling's height,ground diameter,dry matter accumulation and height to diameter ratio.Seedlings height increased with the application amount of biogas liquid,while the ground diameter,dry matter accumulation and the height to diameter ratio tended to be increase firstly and then decreased.Rubber trees in our experiments belong to annual growth type seedlings and in every growth period,biogas liquid application accelerated seedlings growth.In detail,July-September is the main height increment period,May to July is the main growth period of ground diameter.In biogas application gradient experiments,the height increment the most in T6 group?90 m3·hm-2?,which increased 97.5%compared with the T0.Root diameter increased most in T4 group?60 m·hm-2?,which increased 158.62%more than that of T0.The dry matter accumulation rate was the largest in T5?75 m3·hm-2?,which was 201.51%higher than that of the T0 group,and the dry matter accumulation of the aboveground part increased by 205.67%,while the underground part reached 197.77%.Minimum ratio of height to diameter ratio appeared in T4?60 m3·hm-2?,and maximum ratio appeared in T6?90 m3/hm2?.The order of the effect of the amount of biogas on seedling quality index was as follows:T4>T3>T5>T2>TO>T1>T6.2.The effects of biogas liquid application on the contents of nitrogen,phosphorus and potassium in rubber seedling leaves showed that:Compared with the control group,the total nitrogen content of leaves decreased after the application of biogas liquid.With the amount of biogas liquid application increase,the total nitrogen content of the leaves decreased firstly and then increased.The highest total nitrogen content of leaves was found in T1 test group which was 14.76 g·kg-1,while the lowest(13.54 g·kg-1)was found in T3 group.There was significant differences among groups?P<0.05?.The application of proper amount of biogas liquid contributed to the accumulation of total phosphorus in leaves.With the increase of the application amount of biogas liquor,the total phosphorus content increased firstly and then decreased.The highest total phosphorus content was found in T4 group,which was 2.17 g·kg-1 and the lowest was T6(1.81 g·kg-1).Different from total nitrogen and phosphorus,medium and high amount of biogas liquid application had a more obvious promoting effect on the total potassium content of leaves,and the low biogas liquid application amount could reduce the highest total potassium content of leaves.The maximum and minimum potassium content were found in T3(10.43 g·kg-1)and T2 group(7.69 g·kg-1)respectively.The results of Duncan multiple comparisons showed significant differences among the experimental groups.3.Effects of biogas liquid application on rubber plantation soil physical,chemical and biological properties were shown as follows.The application of biogas liquid can increase soil moisture retention and fertilizer retention function.Proper application of biogas liquid can help to maintain soil water content and increase the contents of organic matter,total nitrogen,total phosphorus,total potassium,alkali-hydrolyzed nitrogen,available phosphorus and available potassium.And the above effects were obvious“surface aggregation" in the vertical distribution.The response of various fertility factors to the amount of biogas liquor is different,but overall the effects of medium dose application of biogas liquid?45 m3·hm-2?60 m3·hm-2?is most significant in improving soil available nutrients.The application of biogas liquid can increase the activities of urease,catalase and acid phosphatase,and inhibit the activity of polyphenol oxidase.The effect of biogas liquid application on enzyme activity was obviously different in time scale and space scale,but in general,the promotion effect of biogas liquid application on urease,catalase and acid phosphatase activity was most significant in medium and high amount.4.The results of soil quality evaluation in test areas showed that the optimal uptake range of biogas was different in rubber forests of different forest ages.The optimal capacity of uptaking biogas liquid in 10 years old for rubber plantation is 30 m3 ·hm-?45 m3·hm-2,which was equal to nitrogen 18.72?37.04 kg·hm-2,Phosphorus?P2O5?4.77?7.33 kg.hm 2,Potassium?K2O?25.08?42.66 kg·hm-2;The optimal digestibility of biogas liquid in 30 years forest is 60 m3·hm-2?75 m3·hm-2.which was equal to nitrogen 37.44?61.73 kg hm-2,Phosphorus?P2O5?9.54?12.23 kg·hm-2,Potassium?K2O?50.16?71.10 kg·hm-2.5.According to the results of principal component analysis,the MDS of soil quality evaluation of rubber man-made forest of different ages were selected,among which the MDS of indoor potted rubber seedlings were organic matter,available phosphorus,catalase and polyphenol oxidase.The MDS of 10 years rubber plantation were organic matter,available phosphorus,total potassium and catalase.The MDS of 30 years rubber plantation was pH,total phosphorus,catalase and polyphenol oxidase.These soil factors can basically cover previous existed soil quality information,thus could effectively explain the soil quality situation in the study area.6.In this study,the optimum nitrogen,phosphorus and potassium content of rubber plantation ecosystem in biogas slurry experiments was used as a reference,and combing the soil structure and ecological function,and the energy ecological model of "hog-biogas slurry-rubber" was estimated and optimized.We suggested that the standard unit of the capacity of digesting biogas in 10 year old rubber forest per mu was 18 pigs,in 30 year old rubber forest per mu was 30 pigs based on the safe absorption of biogas slurry. |
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