| The special geographic environment and human activities led to the fragile ecological environment,serious soil erosion and the lower agricultural production in the semi-arid Loess Plateau.Newly-built terraces are a more effective way to reduce soil erosion.However,the soil fertility of newly-built terraces is low and crop yields are difficult to increase.This study takes the newly built terraces as the object,adopted three tillage treatments:flat plot without plastic film(Flat),double ridges and furrows without plastic film(No-mulching),double ridges and furrows with plastic film(Mulching)and four fertilization treatments:only inorganic fertilizer(NP),inorganic fertilizer with sheep manure(NPM),inorganic fertilizer with maize straw(NPS)and double inorganic fertilizer with maize straw(2NPS).Among them,the total nitrogen and phosphorus input of NP,NPM,NPS was the same,the total carbon input of NPM and NPS was the same,and 2NPS was twice that of NPS.So there were twelve treatments in total in the experiment:(1)F-NP:flat plot without plastic film+only inorganic fertilizer;(2)F-NPM:flat plot without plastic film+inorganic fertilizer with sheep manure;(3)F-NPS:flat plot without plastic film+inorganic fertilizer with maize straw;(4)F-2NPS:flat plot without plastic film+double inorganic fertilizer with maize straw;(5)N-NP:double ridges and furrows without plastic film+only inorganic fertilizer;(6)N-NPM:double ridges and furrows without plastic film+inorganic fertilizer with sheep manure;(7)N-NPS:double ridges and furrows without plastic film+inorganic fertilizer with maize straw;(8)N-2NPS:double ridges and furrows without plastic film+double inorganic fertilizer with maize straw;(9)M-NP:double ridges and furrows with plastic film+only inorganic fertilizer;(10)M-NPM:double ridges and furrows with plastic film+inorganic fertilizer with sheep manure;(11)M-NPS:double ridges and furrows with plastic film+inorganic fertilizer with maize straw;(12)M-2NPS:double ridges and furrows with plastic film+double inorganic fertilizer with maize straw.The dynamic change of soil water content of 0-200cm and 0-30 cm soil carbon,nitrogen,phosphorus and pH and crop yield in different treatments were continuously observed.The study began in April 2013.The main results of the 2013-2016 are as follows:(1)Soil moisture content.Compared with the beginning of the experiment(April 2013),0-200 cm soil profile water content increased in September 2013 and September 2014 in all treatments.Among them,0-200cm soil profile moisture content under flat plot without plastic film in September 2013 and September 2014 on average increased by 28.9%and 56.3%,double ridges and furrows without plastic film on average increased by 20.7%and 20.7%,double ridges and furrows with plastic film on average increased by 48.1%and 68.9%.The results show that 0-200 cm soil profile water content was the highest under double ridges and furrows with plastic film.It is more difficult to keep water in double ridges and furrows without plastic film than flat plot without plastic film,and its soil moisture content is the lowest.However,2015 and 2016 was less precipitation.After planting crops,0-200 cm soil profile water content in September 2015 and 2016 was not significant,although the double ridges and furrows with plastic film was higher than the other two tillage treatments in 0-60cm.In April 2013,0-60 cm soil water storage was 86.3 mm.From September 2013 to September2014,there was a significant increase,but decrease from April 2015 to September 2016,which was consistent with the annual precipitation change trend.The results showed that the 0-60 cm soil water storage was significantly higher under double ridges and furrows with plastic film than the other two tillage treatments by 10-38%from September 2013 to September 2016.In addition,in fallow month of October 2015-April 2016,0-60 cm soil water storage increased 6.7,7.8,22.2mm respectively under flat plot without plastic film,double ridges and furrows without plastic film and double ridges and furrows with plastic film.Double ridges and furrows with plastic film increasing amplitude is the largest.Double ridges and furrows with plastic film can effectively collect rainwater in leisure months,reduce evaporation,and increase 0-60cm soil water storage,which is conducive to planting in the coming year.In April 2013,60-200 cm soil water storage was 176.9 mm.The double ridges and furrows with plastic film are significantly higher than the others two by 6.7%-23.5%in September2013-September 2014 and April 2015 and April 2016.After planting crops,however,there was no significant difference between the three tillage treatments in September 2015 and September 2016.(2)Soil organic carbon and pHThe results showed that the 0-30 cm soil organic carbon content and soil pH were significantly affected by fertilization,but the difference between tillage treatments was not significant.Four years after the experiment was set up,soil organic carbon content of NP was 3.42 g/kg,and NPM,NPS and 2NPS is higher 20%,79%and 52%than NP respectively.Compared to only inorganic fertilizer,combined with organic fertilizer increased soil organic carbon significantly,and with the same organic carbon into soil,soil organic carbon content of NPS is significantly higher than NPM.However,the soil organic carbon content did not fold increase in 2NPS.The linear fitting between 0-30 cm soil organic carbon content and the study time was found that the 0-30 cm soil organic carbon content was gradually increased under the four fertilization treatments over the past four years.The rising speed is NPS(k=0.72096,R~2=0.78555*)>2NPS(k=0.59029,R~2=0.87423*)>NPM(k=0.37521,R~2=0.48906)>NP(k=0.17361,R~2=0.1123).In April 2013,the average soil pH was 8.67.Four years after the experiment was set up,all fertilization treatments reduced soil pH.soil pH of NP and NPM was 8.55 and 8.58.However,NPS and 2NPS were 8.44 and 8.35 respectively.Compared with the only inorganic fertilizer and with sheep manure,soil pH under maize straw decreased.(3)Soil nutrientThe results showed that the 0-30 cm soil total nitrogen,total phosphorus and available phosphorus were significantly affected by fertilization,but the difference between tillage treatments was not significant.The content of 0-30 cm soil total nitrogen,total phosphorus and available phosphorus of all treatments showed an increasing trend in four years after the experiment was set up.In April 2013,0-30 cm soil total nitrogen content with an average of 0.35 g/kg.Four years later,soil total nitrogen content of NP was 0.45 g/kg,and the NPM,NPS,2NPS were 1.2,1.6,and 1.5 times than NP respectively.Results show that,compared with only inorganic fertilizer,combined organic fertilizer increased soil total nitrogen content significantly,and with the same nitrogen into soil,soil total nitrogen content of NPS is significantly higher than NPM.However,the soil total nitrogen content did not fold increase in 2NPS.The 0-30 cm total nitrogen content gradually increased with the time,and the increase rate was NPS(k=0.09392,R~2=0.97883*)>2NPS(k=0.08043,R~2=0.82788*)>NPM(k=0.05451,R~2=0.76838*)>NP(k=0.02722,R~2=0.50218).In April 2013,0-30 cm soil total phosphorus and available phosphorus content with an average of 0.60 g/kg and 1.48 mg/kg.And soil total phosphorus content 2NPS was 0.83 g/kg,available phosphorus content was 21.24 mg/kg respectively four years later,0-30 cm soil total phosphorus content of 2NPS higher than NP,NPM and NPS 0.12,0.12,0.08 g/kg respectively,and soil available phosphorus content were higher than 10.09,6.38,7.95 mg/kg respectively,soil total phosphorus and available phosphorus content increases with applying phosphate fertilizer quantity.The 0-30 cm total phosphorus content gradually increased with the time,and the increase rate was 2NPS(k=0.06288,R~2=0.9164*)>NPS(k=0.03935,R~2=0.24814)>NP(k=0.03235,R~2=81748*)>NPM(k=0.03008,R~2=0.41267).Four years after the experiment was set up,the content of 0-30 cm soil organic carbon,total nitrogen and total phosphorus has been gradually approaching or even exceeding the soil parameters level of the old local farmland in this study.Up to September 2016,the 0-30cm organic carbon content reached 46.9%of the local old farmland,and the soil total nitrogen content reached 60.6%under NP.The soil organic carbon content reached 59.1%and the soil total nitrogen content reached 72.9%under NPM.The soil organic carbon content has reached 81.1%of the local old farmland,and the soil total nitrogen content reached 99.1%under NPS.The soil organic carbon content has reached 71.5%of the local old farmland,and the soil total nitrogen content reached 90.7%under 2NPS.However,the soil total phosphorus content is greatly affected by the amount of phosphate fertilizer applied,and the 2NPS treatment has reached 109.4%,which means that it has already exceeded the local old farmland level and NP,NPM and NPS all reached over 90%.(4)Crop yieldTillage and fertilization have significant effects on the yield of broad bean,and there were considerable interactions between them.Under the three tillage treatments,the yield of broad bean was double ridges and furrows with plastic film(3114 kg/ha)>flat plot without plastic film(2411kg/ha)>double ridges and furrows without plastic film(2204 kg/ha).Under the four fertilization treatments,the yield of broad bean was NPS(2806kg/ha)>2NPS(2740kg/ha)>NPM(2474kg/ha)>NP(2285 kg/ha).Among them,the yield of broad bean was the highest under MNPS,which was 88%higher than that of FNP.However,tillage and fertilization have no significant influence on the water utilization efficiency of broad bean and no interaction.Tillage has a significant effect on potato yield and water utilization efficiency,and the difference between fertilization treatments is not significant.Under the three tillage treatments,the yield of potato and the water utilization efficiency were was significantly higher under double ridges and furrows with plastic film than flat plot without plastic film and double ridges and furrows without plastic film,and potato yield was raised 66%and 79%,the water utilization efficiency was raised 65%and 47%respectively.The path analysis results showed that the yield of broad beans was influenced by the 0-30 cm soil mineralization nitrogen content and the 0-200 cm soil water storage,and the determination coefficient was 66%.The potato yield was mainly affected by the content of 0-30 cm soil total nitrogen and mineralized nitrogen,available phosphorus and 0-60 cm soil water storage,and the determination coefficient was 75%.So combined with tillage and fertilization to improve soil moisture content and nutrient status is an effective way to enhance crop yield in newly-built terraces.In conclusion,The present research suggest that double ridges and furrows mulching with plastic film significantly increased soil moisture content,and application of the inorganic fertilizer combined with organic fertilizer can improve soil quality,especially the maize straw,and increased crop yields in newly-built terraces. |
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