Study On The Carbon Properties Of Soil And Benefits Of Different Rice-Crab Production Modes

Concurrent rice and crab farming is an important ecological agricultural process inChina’s northern rice growing area. The popularization and application of rice-crab mode mayhave significant ecological, economic and social benefits. Recently, organic rice-crabproduction mode is quietly rising with the development of organic agriculture, but thetechnology of the organic rice-crab production is still not very mature. In this studyconsequently, effects of the organic rice-crab(M1～M4)(M1, M2, M3and M4mean nochemical fertilizer, and pig manure applied at the rate of48000,42000,36000,30000kg·hm-2,respectively), conventional rice-crab(MNP) and rice monoculture(CK) production modes onthe carbon properties of soil, the rice yield and rice grain quality were investigated throughfield experiments and laboratory analysis in2009and2010, which combining with practicalcondition of the northern rice production and the development of organic rice-crab production;The differences of energy flow, material flow and value flow of different modes werecompared; At the same time, environmental impacts of rice with organic rice-crab (M1),conventional rice-crab(MNP) and rice monoculture (CK)modes were assessed using lifecycle assessment(LCA) methodology in order to supply advices for choosing appropriate riceproduction mode, soil fertilizer system and strengthening the agricultural environmentmanagement of this region. The main conclusions are as follows:1. The organic rice-crab modes can significantly improve the organic-inorganic complexstatus and the combining forms of humus in soil. In2009and2010, after applying the organicrice-crab modes, the content of organic carbon and heavy fraction organic carbon in soils andthe quantity of organo-mineral complex can remarkably increased and the degree oforgano-mineral complex decreased with the increasing of the quantity of additionalorgano-mineral complex and the degree of additional organo-mineral complex of soils;Meanwhile, the content of loose, stable and tight combined humus were also significantlyincreased, especially loose combined humus, and the proportion of loose combined humus toheavy humus and ratio of loose to tight combined were also increased, which activated thecombined soil humus; The effect of the high organic manure rice-crab mode (M1) was the best in organic rice-crab modes. A similar trend was also observed in conventional rice-crabproduction modes,but all the index were obviously lower than that of the organic rice-crabmode. The quantities of organic-inorganic complex and the combined forms of humus aretended to decline by the negative effect of aforementioned indices of the CK mode.2. The applying of organic rice-crab modes can significantly increase the quantity andimprove quality of soil humus. In2009and2010, the soil humic substance extractedcarbon(HEC), humic acid carbon(HAC) and fulvic acid carbon(FAC), Hu min carbon(HMC),loose combined HAC, FAC, the ratio of HAC/HEC and the proportion of loose combinedHAC to loose combined humus carbon were significantly higher in the organic rice-crabmodes, while the ratio of FAC/HEC and the proportion of loose combined FAC to loosecombined humus carbon was decreased, the ratio of HA/FA were also significantly increased.And the most significant increase in organic rice-crab modes were observed in the highorganic manure rice-crab modes (M1, M2). The ratio of FAC/HEC was higher in MNP andCK modes than in the organic rice-crab modes, while the ratio of HA/FA was decreased. Thevalue of HAC and loose HAC E4/E6,△log k in three modes were expressed the samegeneral trend as organic rice-crab＞conventional rice-crab＞rice monoculture.3. The organic rice-crab modes can significantly increase the content of labile organiccarbon fractions. The total organic carbon (TOC), labile organic carbon (LOC), moderatelylabile organic carbon (MLOC), highly labile organic carbon (HLOC) and carbonmanagement index (CMI) were significant or dramatically higher in the organic rice-crabmodes than in the before disposal, and this increase was greater with the increasing amountsof organic manure. A similar but less significant trend was also observed between the organicand conventional rice-crab production modes. The MLOC and CMI were increased slightly inrice monoculture mode, but the other indexes were lower.4. The organic rice-crab modes can significantly enhance the rice yield and improve therice grain quality. In2009and2010, the grain number per panicle, seed setting rate and1000grain weight were higher in the organic rice-crab modes than in the conventional rice-craband rice monoculture modes, and this increase was greater with increasing amounts oforganic manure, especially the most significant increases in the grain number per panicle,seed setting rate and1000grain weight are11.90%,8.42%and3.94%, respectively, which were observed in the high organic manure rice-crab mode (M1), and ultimately improve therice yield. In addition, the crab yield in2009and2010had the same general trend as M1＞M2＞M3＞MNP＞M4. The rice quality was also improved, such as the organic rice-crabmodes significantly decreased chalky rice rate, chalky degree and amylose content decreased,and increased the contents of rice protein, essential amino acid and Fe, Zn. No significantimpacts were observed on the milling quality. However, the Cd, Pb of brown rice are tendedto increase in the high organic manure rice-crab mode (M1) when compared with theconventional rice-crab and rice monoculture modes.5. The structure of energy and material flow in organic rice-crab modes is morereasonable and with higher economic benefits. The ratio between organic energy and manualsupplementary energy were97.67%,97.37%,96.96%and96.49%, respectively in theorganic rice-crab (M1～M4)modes, with respectively11.12%,10.83%,10.41%and9.84%higher than in MNP mode, and95times of the CK mode; The organic rice-crab modes had ahigher energy circulation index than MNP and CK modes, but had slightly lower lightutilization efficiency and energy translation efficiency than in MNP and CK modes.According to the surplus of nutrition system, the N, P2O5and K2O surplus amount and thenutrition flux in organic rice-crab modes were significantly higher than that in MNP and CKmodes. In view of the economic benefit produced, the organic rice-crab (M1～M4) modescould obtain an additional income of7087.50,6649.65,5910.30and4752.00Yuan·hm-2when calculating the organic product as30%higher price of normal product.6. In2010, the highest increase in the TOC(15.15%), HOC(11.96%), HEC(10.79%),HAC(19.34%), Ⅰ C(20.78%), ⅠC/HOC(7.89%), the value of HAC E4/E6(5.62%) and△logk(5.48%) compared to2009was found in the high organic manure rice-crab mode (M1);However, the highest increase in LOC(10.11%)、MLOC (5.14%) and CMI(14.79%) wereobtained in the moderate organic manure rice-crab mode (M3); Similarly, the most significantincreases in the ⅡC, ⅡC/HOCand Ⅰ C/Ⅲ Cwere23.09%,15.26%and12.83%,respectively, which were observed in the low organic manure rice-crab mode (M4).7. The CK mode showed the greatest life cycle environmental impact for rice production,the second was MNP mode and followed by M1mode. In the above results, the life cycle environmental impacts in sequence of rice in organic rice-crab(M1) mode is aquaticeutrophication>environment acidification> energy depletion> global warming, with theimpact indices of0.60、0.07、0.000029and-0.03respectively; the life cycle environmentalimpacts in sequence of rice in conventional rice-crab(MNP) mode is aquatic eutrophication>environment acidification> energy depletion> global warming, with the impact indices of0.58、0.099、0.000036and-0.01respectively; the life cycle environmental impacts insequence of rice in rice monoculture(CK) mode is aquatic eutrophication>environmentacidification> global warming> energy depletion, with the impact indices of0.628、0.124、0.012and0.00004respectively.