| With the progress of the society,continuous improvement of people’s living standards as well as the increasing awareness of environment protection,organic agriculture presents a huge market potential and development space.Ningxia province,with unique regional advantages and environmental conditions,becomes a production base for multiple-crop-ayear organic crops that long-term cultivated.The main fertilizer applied in organic agriculture production is organic fertilizer,in which the organic nitrogen is the main nitrogen that needs to be mineralized into inorganic nitrogen before it can be absorbed and utilized by crops.Therefore,Nitrogen nutrient has become a key factor restricting the development of organic agriculture.In order to maintain the high yield of crops,farmers constantly increase the amount of organic fertilizer in production,which not only fails to improve crop yield,on the contrary,causes waste of fertilizer,increase production cost and leads to environment pollution.This paper first studied the effects of manure combined with biochar on the yield of organic crops and manure nitrogen utilization,and provided a new technical approach for organic farmland nitrogen management.Second,this article,based on the test results of manure combined with biochar,set up experiments with different manure dosage,and explore the appropriate amount of low-cost manure without biochar application.Third,through the analysis of the soil nitrogen mineralization characteristics,the law of soil water and nitrogen migration,the distribution characteristics of organic fertilizer nitrogen,and the key microbial changes in nitrogen conversion under different manure dosage,it was clarified that manure increased organic crop yield and nitrogen fertilizer utilization mechanism,provided theoretical basis and reference for improving the utilization efficiency of manure nitrogen in organic cultivation soil,reducing application costs and tapping the potential of soil manure.This study carried out a one-year field application of biochar test,a one-year field net bag in-situ cultivation test and two-year field plot test containing 15N micro-area test in Ningxia,of which the field test used organic Chinese Flowering Cabbage as the test Materials,field application of biochar test was carried out in 2016,the treatments included:110 t·hm-2 manure(OF),combination of OF+8.5 t·hm-2 biochar(OF+B8.5),combination of OF+17 t·hm-2 biochar(OF+B17),no OF and biochar as control,each treatment was repeated for 3 times.The field plot test containing 15N micro-area test was carried out in 2016 and 2017,respectively,and three crops were planted each year,with a total of 5 organic fertilizer addition levels.They were 0 kgN·hm-2(M0),300 kgN·hm-2(M300),600 kgN·hm-2(M600),900 kgN·hm-2(M900)and 1200 kgN·hm-2(M1200),respectively.Each treatment was repeated for 3 times,with a total of 15 cells.Within the cells,a 15N micro zone with a diameter of 50 cm and a length of 110 cm was covered.In situ culture experiment of net bags in the field,five treatments were set,which were no organic fertilizer(ON0),soil-to-manure ratio 100:1.03(ON300),soil-to-manure ratio 100:2.06(ON600),soil-to-manure ratio 100:3.09(ON900),soilto-manure ratio 100:4.12(ON1200),each treatment was repeated for 3 times.The main results are as follows:1.Clarified the better and best manure nitrogen management plan for three-crop-a-year in dry-lands of NingxiaIn organic farmland,manure combined with low-level biochar could significantly increase the nitrate nitrogen content in the topsoil(0-20 cm),inhibit the leaching down,promote crop growth,increase yield,improve the quality of vegetable sprouts,and increase manure’s N utilization efficiency and economic benefits,which was a better plan of manure N management.Compared with the OF treatment,the average content of NO3--N of the topsoil of OF+B8.5 and OF+B17 was increased by 2.3%and 7.5%,respectively,while the content of NO3--N of the subsoil(20-40 cm)reduced by 20.3%and 9.2%,respectively(P<0.05).The results showed that biochar had a certain ability to hold NO3--N in organic cultivated soil,which could effectively inhibit its leaching into the subsoil and increased the available nitrogen content in 0-20 cm soil layer.As a result,highest vegetable growth,vegetable sprouts long,vegetable sprouts crude,yield and N-uptake were observed under OF+B8.5.Compared with OF,the annual total yield and nitrogen absorption of OF+B8.5 increased by 47.6%and 43.5%,respectively(P<0.05).Meanwhile,NAE increased by 52.2%(P<0.05),and the net income increased by 42.3%(P<0.05).However,the crop yield,nitrogen absorption and net income of OF+B17 were significantly lower than those of OF+B8.5.The results showed that low level biochar application was more beneficial to the production of organic crops in dry-lands of Ningxia.M900 could promotes the growth of OFCC,increases the yield,improves the quality of cabbage stalks,and increases the manure’s N utilization efficiency,and the greater the increased in yield with the extension of the cultivation period.M900 applied less manure than OF+B8.5 and had has better effect,so it can be used as an alternative fertilization mode OF OF+B8.5.The plant height,number of leaves,stalk length,stalk thickness and biomass of M900 were the highest among all treatments during the test period.The yield,nitrogen uptake,manure N recovery efficiency(NRE)and manure N agronomic efficiency(NAE)of OFCC were also highest in M900.The total annual yield and NAE in 2016 were increased by 6.5%and 128.0%,respectively,compared with M1200 treatment(P<0.05),compared with OF+B8.5,and by 28.8%and 39.5%,respectively,compared with OF+B8.5(P<0.05).The results showed that M900 could uptake and utilize manure N to a greater extent to achieve a higher yield under the experimental conditions,which was better than the conventional fertilizer with low amount of biochar.The content of vitamin C(Vc)and reducing sugars in vegetable sprouts was significantly increased after fertilization and the quality of vegetable sprouts was improved.The growth index,biomass and yield of all fertilization treatment in 2017 were slightly higher than that in 2016,and the yield of manure increased with the extension of fertilization period.2.Revealed the mechanism of manure increased the OFCC yield and the manure N utilization efficiency under different manure dosageNitrogen mineralization in organic cultivated soil showed obvious mineralization characteristics of "first fast,then slow".Increasing manure increased the nitrogen mineralization potentia,and it was affected by soil moisture and temperature.The amount of mineralization within 0-60 days of each treatment has accounted for 49.1%-57.3%of the total nitrogen mineralization during the incubation period,and the average daily mineralization was 1.85-5.64 mg·kg-1,while the average daily mineralization after 60 days was only 0.19-0.44 mg·kg-1 indicating that soil nitrogen mineralization was rapid within 060 days and stabilized after 60 days.Soil cumulative net nitrogen mineralization,net nitrogen mineralization rate,mineralization potential(N0)and mineralization rate constant(k)were significantly positively correlated with the amount of manure applied(P<0.001).The regression analysis showed that nitrogen mineralization potential under M0 was 183.91 mg·kg-1,and increaseing 1 kgN·hm-2 would increase the soil nitrogen mineralization potential by 0.053 mg·kg-1 indicating that application of manure could promote soil nitrogen mineralization.Incubation period 0-60 and after 300 days,the temperature increased,and the nitrate nitrogen content also also increased,60-300 days temperature reduced,and the nitrate nitrogen content also reduced,the average moisture content of each treatment continued to increase with the amount of manure,and was significantly positively correlated with the average nitrate nitrogen content,cumulative net nitrogen mineralization and mineralization potential during the cultivation period(P<0.05).The results showed that temperature and moisture were important environmental factors affecting nitrogen mineralization in organic cultivation soil.Compared with M0,the water content of the topsoil(0-20 cm)under M900 increased by 15.8%while the variation range was reduced.Since the irrigation amount in each treatment was the same,there was no significant difference in the water storage of 0-100 cm before and after harvest,and 0-40cm soil water storage increased significantly while 40-100cm soil water storage decreased with the increased of manure.Therefore,M900 has the effect of increasing the topsoil moisture content,reducing the range of change,inhibiting the infiltration of irrigation.The average NO3--N content of topsoil and subsoil(20-40 cm)did not increased continuously with the increased of manure dosage.There was no significant difference between M900 and M1200,but them was significantly higher than M0,M300 and M600 treatments.Compared with all treatments with lower amounts of manure,M900 showed no significant difference in NO3--N content in 40-100 cm soil.The results showed that M900 could improve the NO3--N content in 0-40 cm soil layer and had no significant influence on the NO3--N content in 40-100 cm soil layer.0-20 cm soil electrical conductivity,organic carbon,total nitrogen,available phosphorus,and available potassium were all positively correlated with the manure dosage(P<0.05),soil bulk density decreased significantly after fertilization,organic carbon and total nitrogen content in 2017 were higher than in 2016 under the same manure dosage,indicating that manure could improve the soil nutrient status,and the longer the fertilizer application time increases.The bulk density of M900 in two years was 1.23 and 1.21 g·cm-3,respectively,which were suitable for root growth of the straight plant.Research results based on the 15N microzone showed that the applied manure N could be absorbed by crops very little,most of which remain in the soil or loss.The absorption and utilization of manure N in M900 had reached the maximum with less loss,and the nitrogen absorption would no longer increase if the manure N dosage was increased.With the increase in the manure N dosage,the 15N absorption of organic Chinese Flowering Cabbage did not gradually increase,but showed a "low-high-low" trend.The highest 15N absorption amount and absorption rate both appeared in the M900.M900 was 1/4 lower than that of M1200,but the total annual 15N absorption was 64.3%higher(P<0.05).The ratio of manure N absorbed by OFCC in M300 treatment was higher than that of soil N,while the ratio of manure N absorbed by M900 increased significantly,exceeding soil N by 76.16%.After three cropping cycles,only 10.2%-24.0%of the manure N could be absorbed by the crops,and 39.0%-54.3%of the manure N remained in the 0-100 cm soil layer,and 35.5%-48.5%were loss by various ways.The 15N residual in the soil profile was mainly distributed in the 0-40 cm soil layer,and the residual amount was 127.65-390.32 kg·hm-2,accounting for 78.1%-81.3%of the total residual amount.The 15N residues in the soil under M900 and all lower fertilization treatments were greater than the loss,and there was no significant difference in the loss rate between the treatments.The NO3--15N in 40-100 cm soil layer showed the same change characteristics,indicating that the manure N loss was less under that of M900.Ammonia-oxidizing bacteria(AOB)in cultivated soils play a leading role in the key step of nitrification.High throughput sequencing found that the richness and diversity of AOB(Ace and Shannon)in all samples were higher than that of ammonia oxidizing archaea(AOA).Among them,Ace and Shannon indices of AOB treated with M900 were 53.2%and 57.7%higher than AOA,respectively(P<0.01),soil nitrification potential(PNR)was significantly positively correlated with AOB amoA gene abundance,but not significantly correlated with AOA.Principal co-ordinates analysis(PCoA)showed that the smaller the difference in manure dosage between treatments,the more similar the structure of ammoniaoxidizing microorganisms(AOMs)was,and the larger the difference in manure dosage was,the larger the difference in microbial community structure was,indicating that the manure dosage significantly changed the structure of AOMs.Pearson correlation analysis showed that soil AOB amoA abundance and AOB/AOA amoA abundance ratio and soil electrical conductivity,total carbon,total nitrogen,nitrate,effective phosphorus,available potassium and total organic carbon was positively related(P<0.05),indicating that these physical and chemical parameters were important cause for changes of AOMs community structure.Nitrosomonas belonging to AOA and Nitrososphaera belonging to AOB can growth better under M900 and higher manure dosage,while Nitrosopilus and Nitrosopira can growth better under M600 and lower manure dosage. |
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