| To solve the problems of low water and fertilizer utilization rate,no optimal combination scheme of water and fertilizer regulation,stock density of crab and feed quantity in rice-fishing mode in Helan County,Ningxia,orthogonal test and random block design were adopted.The effects of different paddy water depth,application amount of marsh and nitrogen fertilizer,crab density and feed amount on the growth,yield and quality of rice and river crab under rice-fishing mode were systematically studied,which has important guiding role and practical significance for improving the quality and efficiency of rice-fishing mode and constructing modern ecological irrigation area in Ningxia.The main research results are as follows:(1)Four-factor three-level randomized block test was used to study the effects of different depth of water layer(H),fertilization(F),stock density of crab(D)and daily feed quantity(S)on growth,photosynthesis,yield and quality of rice,and body shape indicators,nutrient composition,mineral elements and contents of crab’s amino acid.The experiment concluded the primary and secondary factors of different factors on growth index,yield and quality of rice and crab,single factor variation rule and optimal combination scheme of factors.The results showed that:the rice photosynthesis(Pn,Gs,Tr,SPAD)increased with the increase of H and F,and increased first and then decreased with the increase of D and S.According tothe range and variance analysis,H and F has significant effects on Pn,but D and S is not significant,the order of four factors was F>H>D>S.The yield of both rice and crab increased with the increase of water layer depth and fertilization,the yield of rice first increased and then decreased with the increase of D and feed quantity;The yield of crab significantly increased with the increase of D,and first increased and then decreased with the increase of S.The range and variance analysis of yield were conducted.And the order of the four factors affecting the rice yield of rice and crap was F>H>D>S and D>H>F>S.The four factors had significant effects on the yield of rice and crab.The rice sensory evalution increased with the increase of H and S,and first increased and then decreased with the increase of F,and decreased with the increase of S.The range and variance analysis showed that H,F and S had significant effects,but D had no significant effects,and the order of factors was H>F>S>D.The contents of crude protein,ash,total amino acid(TAA)and Ca in crab muscle increased with the increase of H and F.Except that the contents of Ca decreased with the increase of S,the others increased first and then decreased with the increase of D and S.The range and variance analysis showed that H and F had significant effects on the above indexes,but D and S had no significant effects.The order of each factor on the contents of TAA and Ca was H>F>D>S.Compared with the initial soil of paddy,the soil nutrients of paddy’s soil in the later stage of rice maturation were increased to different degrees,among which the alkali-hydrolysed nitrogen,available phosphorus,available potassium and organic matter were increased respectively by 32.1%～86.5%,2.8%～109.1%,61.9%～91.5%and 5.1%～72%.PH and water soluble salt content decreased by 0.9%～4.3%and 33.5%～47.3%respectively.The content of soil organic matter increased with the increase of the four factors.The range and variance analysis showed that H and F had significant effects,but D and S had no significant effects.The order of factors was H>F>S>D.Considering the primary and secondary factors,significance,the comprehensive cost and economic benefit of rice-crab model,the optimal level combination was determined as H3F3D2S1,that is,the H was 11cm,the F was 6+300+400kg/667m~2(urea+biogas residue+biogas slurry),and the D was 6kg/667m~2,the S was 480g/667m~2,the yield of rice and crab was the highest,which respectively were 685.32kg/667m~2 and 29.64kg/667m~2.At the same time,the quality of rice and crab muscle was also better,the rice sensory evalution was 83.7 points,the total amino acid of crab meat was 15.85g/100g,and soil nutrient content was relatively high.The soil organic matter content was 14.53g/kg,which had the best improvement effect on saline-alkali rice field.(2)Two-factor three-level randomized block experiment was used to study the effects of different water depth(H)and nitrogen application(F)on growth,photosynthesis,yield and quality of rice,and body index,nutrient composition,mineral elements,amino acid of crab Research shows that:In terms of rice,the growth,photosynthesis,yield and quality of rice under low fertilizer(H1F1)in shallow water layer were better than those under medium water-fertilizer(H2F2)control and the other 7 treatments.Compared with H2F2,plant height of rice,net photosynthetic rate and yield of rice under H1F1 treatment were increased by 8.92%,30.72%and 11.41%.Gel consistency and sensory evalution of rice were respectively increased by 5.5%and 2.9%.In terms of crab,the growth,yield and quality of crabs of low fertilizerin and deep water layer(H3F1)were better than those of H2F2 and the other 7 treatments.Compared with H2F2,the body weight and length of crab of H1F1 increased by 14.8%and 30.7%,and the yield of crab increased by 9%.Crude protein content and total amino acid content of crab muscle increased by 18.9%and 14.2%.Considering the economic benefit and the cost of rice and crab,under the premise that the local rice is the main body,the rice and crab mode with "10+20" cm shallow water layer and "4+10" kg/667m~2 nitrogen application has the best effect on the improvement of quality and efficiency of rice and crab,and yield of rice and crab were 597.25 kg/667m~2 and 28.12 kg/667m~2 respectively.The rice sensory evalution was 76.8 points,and TAA of crab muscle was 14.31%.(3)By contrast tests,paddies with low application rate of biogas slurry(B1)and biogas slurry with high application rate of biogas slurry(B2)and ring ditch were set as treatment,and conventional topdressing urea paddies and ring ditch were taken as control(CK)in both the rice-grass crap and rice-crab modes.The effects of biogas slurry on body index,general nutrients,some mineral elements and amino acid contents of grass carp and crab were studied.The results showed that the body indexes of grass craps and crabs treated with biogas slurry were better than those of the control treated with chemical fertilizer.The body indexes of grass craps and crabs under B1 were better than those of B2,The order of fish and crabs yield was B2>B1>CK.In addition,proper application of biogas slurry could improve the water holding capacity of grass carp,but excessive application of biogas slurry was not conducive to the storage and processing of grass carp.The drip loss of B1 and B2 was significantly reduced by 17.4%and 12.4%compared with CK.The muscle moisture content of both grass crap and crab was decreased with the increase of biogas slurry application rate,but the differences were not significant(P>0.05).The order of muscle pH was as follows:B2>B1>CK,and there were significant differences(P<0.05).Compared with CK,the pH of B1 and B2 male crab muscle was significantly increased by 5.8%and 12.1%,and that of fish muscle was significantly increased by 10.4%and 17.9%.In terms of nutritional quality,the contents of crude protein,phosphorus,iron and calcium in muscle were all in the order of B1>B2>CK,and there were significant differences among different treatments,and there were also significant differences between different sexes of crab.In terms of amino acids,17 kinds of amino acids were detected in both grass crap and crab,and the total amino acids(TAA)of grass crap and crab treated by biogas slurry were significantly higher than that of chemical fertilizer control.Compared with CK,the increments of B1 and B2 in crab were 24%and 17.7%,and that in grass carp was 16.7%and 12.6%,but there was no significant difference between B1 and B2.TAA of crab roe was significantly higher than that of crab ointment.The order of essential amino acid index(EAAI)was B1>B2>CK.In conclusion,proper application of biogas slurry in rice field can improve the growth and development of grass carp and crab,and contribute to the accumulation of nutrient components and the enhancement of muscle flavor of grass carp and crab,but excessive application of biogas slurry has a negative effect.Finally,under the premise of 723.3mm and 709.3mm evaporation of water surface and 123.7mm rainfall during the rice growth period,it was determined that the growth and quality of grass carps and crabs treated by B1 were better.And the optimal combination of water and fertilizer was as follows:Irrigation was performed for 13 times,and the depth of water layer in the rice field was kept at 25 cm in the rice-grass carp mode and 15 cm in the rice-crab mode.Biogas slurry was applied for 6 times,the first three times being 200kg/667m~2,and the last three times being 100kg/667m~2.The total amount of biogas slurry was 900 kg/667m~2.The yield of grass carp and crab were 153.62 kg/667m~2 and 31.58 kg/667m~2,and the yield of rice in the two modes were 575.37kg/667m~2 and 592.31kg/667m~2 respectively.The water demand were 692m~3/667m~2 and 656m~3/667M2,and the water production efficiency of rice is 0.84kg/m~3 and 0.9kg/m~3 respectively. |
