Mechanism Of Characteristics In Soil Respiration Under Typical Intercropping Systems On Oasis Arid Land

Intercropping systems have been shown to boost crop productivity and provide potentialfor biodiversity in development of sustainable agriculture. Main concern is that higher yieldingsystems usually are associated with higher soil respiration while soil respiratory responses tocropping systems are limited to know on arid land. Field experiments were conducted atWuwei Experimental Station of Gansu Agricultural University, China （37o96′N,102o64′E）in2009,2010, and2011. Four intercropping systems, including maize （Zea mays）–wheat（Triticum aestivum）, maize–rape （Brassia campestris）, maize–pea （Pisum sativum） andsoybean （Glycine max）–wheat intercropping, along with the respective five sole crops, weredesigned in a randomized, complete block design with three replicates to investigate the effectof intercropping systems on yield–and environment–related factors, and the contributions ofcontrolling factors to those related factors. Main results are summarized as follows:（1） Crop growth （dry matter accumulation） is a major factor controlling soil respirationfarmland. With the increase of dry matter accumulation, soil respiration rate increased,reached a peak at the early flowering stage for earlier sown crops and at the silking stage formaize, and then declined. A quadratic function for dry matter accumulation combined with anexponential function for soil temperature was fit the measured results, showing thecombination of dry matter and soil temperature accounted for38%to58%of variances insoil respiration. Maize based intercropping such as maize–wheat (0.52g CO^-22mhr^-1),maize–rape (0.44g CO₂m^-2hr^-1) and maize–pea (0.51g CO₂m^-2hr^-1) intercropping systemssignificantly reduced seasonal maximal soil respiration as compared to sole maize (0.74g CO₂m^-2hr^-1). Sole maize emitted the highest carbon (4,233kg C ha^-1) in each year, whereas solerape released the least amount (1,260kg C ha^-1). Intercropping (1,701to3108kg C ha^-1)significantly reduced carbon emission compared to sole maize or sole wheat. Maize was thegreatest emitter of carbon per unit of water, followed by pea and wheat, whereas rape andsoybean were the least. Maize based intercropping emitted42%,52%, and45%less carbonper unit of water in2009,2010, and2011, respectively, compared to sole maize.（2） Maize produced the greatest grain yield at11,724kg ha^-1, followed by wheataveraging at6,467kg ha^-1, and pea the lowest at2,830kg ha^-1. Sole maize had the grain yielddecreased from12,677kg ha^-1in2009to10,624kg ha^-1in2011, or by19%, whereas themaize in the maize–wheat intercropping had its grain yields increased from7,404kg ha^-1in 2009to8,123kg ha^-1in2011, or by10%. Although, intercropping consumes more watercompared to sole cropping, maize based intercropping systems had greatest water useefficiency with a land equivalent ratio of1.16to1.48, showing significant advantages in wateruse and yield over the rest of the cropping systems.（3） Pea showed least soil water competition with the intercropped maize in the maize–peaintercropping during the co–growth period. Wheat was the greatest competitor for soil water,and competed for11to20mm soil water from neighboring maize or soybean strips inmaize–wheat or soybean–wheat intercropping systems. Pea was a least competitive crop withshallow rooting system. Wheat recharged greatest amount of soil water from wheat harvestthrough maize harvest, having a potential to compensate19to21mm soil water to the maizestrips, which is favorable to the recovery of maize growth in maize–wheat intercropping.Maize based intercropping, especially maize–pea intercropping, is a promising croppingoption in arid areas, as soil water extraction of two species in intercropping can be temporallystratified.（4） Intercropping had a co–growth period of50–80d, allowing the two intercroppedspecies to complete their life cycles. Maximum dry matter rate for the earlier sown crops in themaize based intercropping systems was significantly greater than that for sole earlier sowncrops (57vs.51g m^-2d^-1) which occurred at around72to77days after sowing （DAS）,whereas the maximum dry matter rate for the later sown crops in the maize basedintercropping systems was between31.6to44.9g m^-2d^-1, or30to43%lower than that ofsole later sown crops. The time to reach maximum dry matter was80–96DAS for sole maize,and the corresponding time for the intercropped maize was delayed by6to10days. Amongmaize based intercropping, maximum accumulation rate of maize in maize–pea intercroppingsystem was43g m^-2d^-1, or15%,21%and40%higher than those of sole maize, maize inmaize–rape and maize in maize–wheat intercropping systems, respectively.