Effect Of Stubble And Tillage Management On Soil Carbon And Nitrate Under Wheat/maize Intercropping In Oases Of The Shiyanghe River Basin

High soil CO2emissions and nitrate leaching can lead to decline in soil fertility, whichcause crop yield decline and environmental pollution. Suitable cropping system and standingmode can enhance soil C sequestration, reduce soil CO2emissions, improve nitrogen (N)uptake efficiency, reduce nitrate leaching, which result in crop yield increase. A fieldexperiment was conducted to investigate the effect of tillage and crop treatments on soil CO2emissions, carbon and nitrogen balance, soil physical properties, and crop yield and growthdevelopment in Gansu Agricultural University Experimental Station in Wuwei city in the theHexi Oasis irrigation, Gansu province during2010to2011. The experiment consisted of threetypes of standing mode: sole wheat, sole corn and wheat/corn intercropping, and four types oftillage pattern: tillage with stubble incorporated, no tillage with stubble standing and tillagewith stubble burning only conducted in2010, no tillage with stubble burning only conductedin2011. The main results are as follows:1. N content in crop seeds was affected by cropping pattern in three standing mode, thebasic law of which was crop seed N content under NTSS was at the first place, crop seed Ncontent under no tillage with stubble burning was at the second place; plant total N uptakediffered among crop species, previous crops and tillage method. In sole wheat, plant total Nuptake did not differ significantly from T and TIS, but higher under TIS and NTSS than underNT; In intercropped wheat, plant total N was not affected by tillage methods; In sole andintercropped corn, when previous crop is wheat, plant total N was higher under NTSS and TISthan under T; when previous crops is corn, plant total N was higher under NTSS and NT thanunder T; results from Comparison of standing modes, plant total N under sole wheat waslower than under sole corn and wheat/corn intercropping for11.47and10.47%, respectively.There were no significant differences existed between sole corn and wheat/corn intercropping.2. Soil nitrate distribution was higher under NTSS and TIS than under other tillagemethod at020cm. when previous crops were wheat, it is significantly higher than corn. Formtwo years experiment results, we found surface soil soil nitrate content of sole wheat underNTSS and TIS was higher than under other tillage method, which can decrease the leaching loss of nitrate from soil; the risk of soil nitrate losses through leaching after stubble return waslower when compared with stubble burning in tillage and no tillage treatment; soil nitrate wasnot changed significantly by tillage at060cm depth layers for sole corn when previous cropsis wheat, but significantly different was found at020cm depth layers when previous crops iscorn. The same trend was found in intercropped corn.3. NTSS can reduce the soil nitrate leaching; T treatment had the highest risk of soilnitrate leaching. The risk of soil nitrate losses through leaching after stubble return was lowerwhen compared with stubble burning for sole wheat in tillage treatment, there was nodifference existed between TIS and T; sole con under NTSS and NT had lower soil nitrateleaching than other tillage method; NTSS and TIS for intercropping system could reduce thesoil nitrate leaching when previous crop is wheat (2010), and this effect is found in no tillagesystem when previous crop is corn (2011). The soil nitrate leaching, in NTSS┚T and TIS,were35.61,49.49and39.67kg hm2in2010, and were38.7┚27.77and21.07kg hm2in2011.Compared with the T treatment, the decreases of soil leaching in the NTSS and TIS were28.04%and10.23%respectively in2010, Compared with the TIS treatment, the decreases ofsoil leaching in the NTSS and NT, were17.63and10.93kg hm2respectively in2011.4. The different treatment of soil respiration rate growth period showed a single peakcurve, the peak appears in the most productive period of crop growth, but the specific peaktimes vary. Soil respiration was significantly lower under no tillage than tillage, the order ofdifferent standing mode was sole wheat> wheat/corn> sole corn. No tillage had moresignificant impacts on soil respiration than residue; different treatment of the diurnal variationof soil respiration showed a single peak curve, diurnal variation of wheat/maize intercropping<monoculture wheat <monoculture corn, the highest soil respiration in daytime under NTSS(14:00) was later than tillage treatment (12:00) for sole wheat, but this was not found in solecorn and wheat/corn.NEP was highest under NTSS in the same standing mode, NTSS for sole wheatincreased NEP compared to TIS and T by1671and1276kg C hm2(2010), and compared toTIS and T by1822and4124kg C hm2, respectively. NTSS for sole corn increased NEPcompared to TIS and T by2248and4231kg C hm2while previous crop is wheat (2010), and compared to TIS and T by1969and1219kg C hm2while previous crop is corn (2011),respectively. NTSS for wheat/corn increased NEP compared to TIS and T by2150and3293kg C hm2(2010), and compared to TIS and T by974and1663kg C hm2(2011), respectively.The NEP, in sole wheat┚sole corn and wheat/corn intercropping, were3186┚4060and4161kg C hm2. Compared with the sole wheat treatment, the increase of NEP in the sole cornand wheat/corn intercropping, were874and975kg C hm2, respectively, carbon sequencewas highest under wheat/corn, and was lowest under sole wheat.5. The grain yield was higher under NTSS than NT; there were no differences underother tillage. NTSS and TIS for sole wheat increased grain yield compared to NT by12.13%and8.80%, respectively. But there were no differences under intercropped wheat, sole corn;NTSS for intercropped corn increased grain yield compared to TIS and T by3.34%and7.24%, respectively. But there were no differences under three tillage methods in2011. Grainyield for wheat/corn intercropping was not impacted by tillage method.6. The NTSS treatments for sole wheat had16.13and20.37C hm2higher WUE thanTIS and T (2010), and9.01%and17.41%higher WUE than TIS and NT (2011). The similartrend were found in intercropped wheat, The NTSS treatments for sole wheat had14.53%and14.87%C hm2higher WUE than TIS and T (2010), and8.66%and12.51%higherWUE than TIS and NT (2011); The NTSS treatments for sole corn had14.53%and14.87%C hm2higher WUE than TIS and T, and for intercropped had8.66%and12.51%higherWUE than TIS and T. There was no difference under tillage while previous crop is corn; TheNTSS treatments for wheat/corn intercropping had12.87%and17.55%C hm2higher WUEthan TIS and T (2010), and7.54%and9.61%higher WUE than TIS and NT (2011).7. Under different tillage method and standing mode, soil respiration was significantlyaffected by soil temperature and crop growth, while soil water content was not a significantaffect factor. Soil temperature was highly correlated with soil respiration rate in05cm soillayer. sole wheat and corn under NTSS showed the lowest regression coefficients betweensoil respiration and temperature, There were no differences existed under different tillage inwheat/corn intercropping when previous crops is wheat/corn. Soil respiration wassignificantly correlated to soil water content in010cm soil depth; soil respiration rate and dry matter accumulation rate showed a significant positive correlation. Under the differentstanding mode, the order of R2was sole wheat> wheat/corn intercropping> sole corn.In summary, from the view of reducing soil carbon emission, reducing nitrate leachingand increasing crop yield and WUE, the most appropriate tillage method and standing modewas wheat/maize intercropping under no tillage with stubble standing in the Hexi OasisIrrigation, nitrate leaching is mainly affected by nitrate distribution and plant nitrate N uptakefrom soil. Soil respiration is mainly affected by both soil temperature and crop growth,wheras soil moisture was not significantly correlated with soil respiration, the impact wasdecreased under intercropping system.