| Rapeseed is the world's important oil crop.China has the largest rape growing area and rapeseed production in the world,but faces with the problem of low rapeseed yield.Yangtze River is the most important rapeseed production base in China and southwest China is the main producing area of rapeseed in the upper reaches of the Yangtze River.As a typical dryland crop,the challenges of rapeseed industry in the southwest dryland were not only that the common problems of water shortage and soil impoverishment in dryland agriculture should be dealt with,but also that environmental pollution caused by excessive fertilization should be considered.With the change of precipitation pattern caused by global climate change,seasonal drought and rainy season became another obstacle to high yield of rapeseed in the dry land of southwest China.Characterized by hills,mountains and backward productive forces,rain-fed agricultural areas in southwest China are difficult to develop the technology of water and fertilizer integration.It is urgent to develop the rapeseed efficient production integration technology suitable for abnormal climate.Water-saving technology with straw mulching and furrow and ridge mulching as the effective measures could reduce the evaporation of dry land,increase the soil water content and improve the utilization efficiency of water and fertilizer.As an efficient fertilizer saving technology,slow-release fertilizer has the advantages of one-time application,long cycle of nutrient supply and improvement of utilization efficiency of crop fertilizers.The integration of water-saving and fertilizer technology and its application to rapeseed production in different climate in southwest dryland are of great practical significance to the efficient utilization of water and fertilizer in dryland rapeseed and the sustainable development of agriculture.In this paper,field experiments for 2 production years were carried out in Baoping town,Yunyang country,Chongqing,China.Three farming patterns were applied:(1)a ridge-furrow rainfall harvesting system(RFRH);(2)straw mulching(SM)and(3)conventional flat planting(CP).Three levels of fertilization(i.e.,100%,80%,60%and 0%)combined with two types of fertilizer(i.e.,Conventional fertilizer(CF)and slow-release fertilizer(SR))were used.The effects of water and fertilizer integration technology on the rapeseed growth and soil microenvironment of rapeseed in dry land were compared.In order to select suitable and efficient planting patterns of southwest dryland rapeseed industry,we studied the effects of water-saving and fertilizer technology on the growth,yield,quality,water and fertilizer utilization efficiency of rapeseed under different precipitation conditions,as well as the spatial and temporal change characteristics and change mechanism of soil nutrients and soil microbial characteristics.The main research conclusions were as follows:1.Fertilization and cultivation patterns had significant effects on plant height,dry matter accumulation and root shoot ratio of rapeseed.Plant height and dry matter accumulation slowed down with the rapid increase of rapeseed growth period,but the root-shoot ratio increased first and then decreased.Under rainy climate,comparing under seasonal drought climate,plant height,dry matter accumulation and root-shoot ratio decreased significantly.In rainy years(2016-2017),the reduced-fertilization I(80%SR)treatment was better to maintain soil nutrient than the conventional fertilizer(100%CF).Under the seasonal drought type(2017-2018),single slow-release fertilizer technology(CP+80%SR,P80)couldn't increase yield,compared to the local habit cultivation(CP+100%CF,PC).Water-fertilizer saving technology(SM+80%SR,J80;RFRH+80%SR,M80)has more advantages.Reduced-fertilization II(60%SR)couldn't fully meet the nutrient needs of rape growth period,which is not conducive to crop growth.2.Fertilization and cultivation patterns could significantly affect rapeseed yield and quality.The number of the effective pod number was the main factor that caused the yield difference of rapeseed.There was no significantly difference in 1000-grain weight and seeds number per pod between different treatments.Compared with the seasonal drought,raininess in growth period was more unfavorable to rapeseed yield,and the yield of rapeseed in the rainy year(2016-2017)decreased by22.81%on average compared with the seasonal drought(2017-2018).J80&M80 increased the yield by 29.46%in rainy year and 3.47%in seasonal drought year.In rainy years,reduced-fertilization I could reduce the nitrogen fertilizer leaching loss and was better than the CF.In seasonal dry years,water-saving technology(SM/RFRH)could provide more water for crop growth and is better than conventional flat planting(CP).The single water-saving/water-saving fertilizer technology could not adapt to different climates,and the reduced-fertilization II could not obtain high yield of rapeseed due to the low fertilization level,and the J80/M80 had more potential for yield increase.Seasonal drought and precipitation anomalies can aggravate the change of quality and main fatty acid content of rapeseed.Rainy years reduced oil content and some fatty acids,while drought years had a greater impact on the composition of fatty acids.In rainy years,the oil content and unsaturated fatty acid content were increased by 7.5%and 2.85%respectively.Under the seasonal drought,the oil content increased by 13.26%and the unsaturated fatty acid content increased by 3.05%.J80&M80 were more beneficial to the stability of rapeseed quality under precipitation anomaly.3.Both fertilization and cultivation mode could affect water consumption,total water consumption and water use efficiency of rapeseed.There was no significant difference in water consumption between different treatments in the period of rapeseed late growth stage(Anthesis&Maturity).J80/M80 in the growth period of two different precipitation years decreased by 29.37%on average,and the water use efficiency(WUE)increased by 6.98%.The negative effect of rainy years(2016-2017)on fertilizer utilization efficiency was greater than that of seasonal drought(2017-2018).In different climates,J80&M80 could improve the apparent utilization rate,agronomic efficiency and physiological utilization rate of nitrogen,phosphorus and potassium fertilizer,and all the increase rate were higher than that of the single water/fertilizer-saving technique.Reduced-fertilization II treatment is not conducive to heighten crop yield due to low fertilization level.The more abnormal rainfall than the seasonal drought had a greater negative effect on the economic benefits of rapeseed production.In different climate,J80&M80 could improve the net output value of rapeseed by 841.48?1695.44 RMB yuan2ha-1 compared with the PC.Compared with M80,J80could further improve the input-output ratio,and was not only better to increase yield but also have advantages of environmental protection4.Fertilization could significantly affect soil organic matter,p H value,total and available nutrients.Under the same cultivation method,the soil p H value decreased with the increase of fertilizer level.At the same fertilization level,there was no significant difference between different cultivation measures.In rainy years(2016-2017),the conventional fertilizer(CF)and reduced-fertilization I increased the soil organic matter by 21.26%and 35.25%respectively compared with that with no fertilizer(CK).They also increased total nitrogen 16.83%and 17.52%,total phosphorus63.23%and 52.17%,and total potassium 16.21%and 28.17%.Under seasonal drought(2017-2018),the CF and reduced-fertilization I increased the soil organic matter by 25.14%and 23.32%respectively on average compared with that without fertilization(CK).Increase total nitrogen 21.83%and 17.52%,total phosphorus 57.23%and 50.43%and total potassium 17.64%and 15.45%.Reduced-fertilization I could be more efficient than the CF in different precipitation conditions.The release of available nitrogen and potassium increased first and then decreased with the rapeseed growth period.The characteristics of soil potassium and nitrogen were similar,and the available potassium was greatly affected by precipitation.Soil phosphorus was less affected by soil water and the available phosphorus changed gently during the growth period of rapeseed.Treatment with slow-release fertilizer(SR)can significantly reduce nitrogen leaching loss in growth period,especially in rainy season.However,the effect of SR was affected by environmental factors,and a large amount of rainfall will shorten the effect of sustained release agent,while single fertilizer technology(CP+80%SR,P80)is not conducive to the release of fertilizer effect in dry climate.J80/M80 could improve soil fertility more than PC under different precipitation conditions.5.Fertilization can significantly affect soil microbial biomass carbon and nitrogen content and soil enzyme activity.The peak of soil microbial content changes could follow the change of precipitation conditions and soil fertility.The release speed of soil fertility in rainy years(2016-2017)was more quickly than the seasonal drought years(2017-2018).So the releasing peak of carbon and nitrogen of soil microbial biomass was also earlier in rainy year than drought.J80/M80 could maintain soil fertility in rainy years and soil water in seasonal drought years,and is more conducive to improving soil microbial carbon and nitrogen than conventional cultivation(PC).In seasonal dry years,the straw mulching(SM)was better than RFRH and CP.Under the rainy years,the main enzyme activity performed like this J80&M80>single water-saving technology(JC/MC)>single fertilizer technology(P80)>reduced fertilizationII>CK.The activity of urease and alkaline phosphatase in soil treated with slow-release fertilizer(low in the early stage of growth)was higher than that of conventional fertilizer(CF).Except the anthesis,the change trend of cellulase activity in soil was similar to urease and alkaline phosphatase.With the development of the growth period,the activity of urease and alkaline phosphatase of all treatments in the mature period tend to have no significant differences.The change trend of sucrase activity in each treatment was the same in two experiment year.The soil enzyme activity fluctuates more slightly in seasonal drought than in rainy climate.The change of enzyme activity of slow release fertilizer(SR)was gentler than that of conventional fertilizer(CF).The soil enzyme activity in rainy years had a tendency to be released much earlier than that in seasonal dry years.J80&M80 were beneficial to maintain the stability of soil enzyme activity under different precipitation conditions.6.Fertilization could significantly affect soil microbial diversity.In rainy years(2016-2017),the total amount of PLFA increased first and then decreased in growth stage,while which first decreased and then increased in the seasonal drought years(2017-2018).Fertilization could significantly increase the PLFA content of soil bacteria,fungi and actinomycetes.Except actinomycetes,the contents of soil bacteria and fungi in seasonal dry years were higher than that in rainy years.The straight chain monounsaturated fatty acid/cyclopropane acid(A/B)ratio characterizing nutrient stress reflects the risk of nutrient loss in rainy years.The bacteria/fungi and gram-positive bacteria/gram-negative bacteria(G+/G-)that characterized the stability of soil microenvironment reflected that the reduced-fertilization I was more benefit to the stability of soil nutrients than conventional fertilizer(CF).In summary,the combined use of straw mulching,furrow and ridge rain water harvesting and slow-release fertilizer technologies benefited rapeseed production both in wet and dry years,and reduced negative environmental effects of cropping,so as to achieve the win-win outcome of simultaneously increasing crop yield and environmental protection. |
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