| The consumption of freshwater for non-agricultural purposes is increasing due rapidindustrial and urban development. This has caused declines both in the consumption of waterfor agricultural purposes and in the proportion of freshwater used for agriculture. Riceproduction must increase to meet the demands of the world’s growing population. A majorchallenge in rice production is to save water while maintaining or even increasing grain yield.The rice production in arid region faces a great challenge because rice plants consume hugeamounts of water. In the regions, such as in Xinjiang province of China, annual precipitationaverages170mm and evaporation averages1200mm. Rice plants consume3000mm ofirrigation water during the growing season (May to October). The water use efficiency is only0.2~0.3kg m-3. If a water-saving technology with high grain yield could be successfullyapplied in arid region, it could provide some important information help to alleviatefreshwater crisis and food security and maintain agricultural sustainability in the future.Plastic film mulch with drip irrigation is a new water-saving rice cultivation technologyfor rice production. Little is known the effect of this method on rice yield and water-use. Weassumed that plastic film mulch with drip irrigation was a superior non-flooded irrigationsystem for rice production in arid areas. Plot experiments incorporation into fieldinvestigations were conducted across three years. The objectives of the present study were tocharacterize and compare rice productivity, growth, development, and adaptation mechanismto current ecological area among plastic mulching with drip irrigation system (DI), plasticmulching with furrow irrigation system/ground cover rice production systems (GCRPSs)(FIM), and no mulching with furrow irrigation system/aerobic rice (FIN). Meanwhile, Plotexperiments with different water regimes were also conducted in plastic mulching with dripirrigation in2012and2013to indentify the demand for the irrigation water at differentphenological phases and the characteristics of population structure for achieving high grainyield and high water use efficiency. The main results were as follows:(1) Population uniformity was most uniform when each sheet of plastic film (1.6m wide)had four drip tapes and eight rows of rice (R1). The second most uniform canopy wasobserved when each sheet of plastic film had two drip tapes and eight rows of rice (R2). Theleast uniform canopy in our study was observed when one sheet of plastic film had one driptape with eight rows rice (R3). In the R2treatment, the rapid growth of rice plants in the rownext to the drip tape made up for the slower growth of rice plants in the second row from thedrip tape. There were no significant differences in grain yield, water use efficiency, and economic return between the R1and R2treatments. However, in the R3treatment, ricegrowth and development was seriously reduced throughout the entire growing season in thetwo rows farthest from the drip tape (i.e., the third and fourth rows). As a result, grain yield,water use efficiency, and economic return were significantly lower in the R3treatment than inthe R1and R2treatments. In conclusion, the distance between drip tapes should be kept in therange of40~80cm (or the horizontal wetting distance of one drip tape should be20~40cm)to obtain high grain yield under DI in silty loam soil.(2) At flowering in the R2treatment, the root distribution of rice in the first row (i.e. rownearest the drip tape) was different from the root distribution of rice in the second row.Generally, root length density (RLD) and root weight density (RWD) of plants in the first rowwere greater than those of plants in the second row. The differences between the rowsdeclined as the irrigation amount increased. The RLD and the RWD were both significantlylower in the DI treatment than in the flood irrigation treatment. The main reason is that bothRLD and RWD at the0~20cm depth were lower in the DI treatment than in the floodtreatment. Correlation analysis showed that increasing root development in a10cm diameterarea around the hill at flowering could be a key factor for obtaining high grain yield and goodagronomic performance under DI.(3) Compared with the CF treatment, grain yields were31.76~52.19%lower in the DItreatment,57.16~61.02%lower in the FIM treatment, and74.40~75.73%lower in the FINtreatment, which were mainly from source limitation, especially a low dry matteraccumulation restricted by photosynthetic productivity during post-anthesis, in the non-floodirrigation treatments. Water use efficiency (WUE) was the highest in the DI treatment, being1.35~1.89times higher than that in the FIM treatment,1.52~2.12times higher than that in theCF treatment, and2.37~3.78times higher than that in the FIN treatment. The yieldcontribution from tillers (YCFTs) was50.65~62.47%in the CF treatment and12.07~20.62%in the non-flooded irrigation treatments. These low YCFTs values were attributed to the poorperformance in tiller panicles rather than the total tiller number. Under non-flooded irrigation,the DI treatment created a relative optimal micro-ecosystem (i.e., soil temperature, canopytemperature and relatively humidity) for rice growth, as a result, the DI treatment has greaterwater saving capacity and lower yield and economic return gaps than the FIM and FINtreatments compared with the CF treatment.(4) Photosynthesis was limited by metabolic processes in the non-flooded irrigationtreatments. The underlying reason for these limitations was that leaf N concentrations werelower in the non-flooded irrigation treatments than in the CF treatment.. Flag leaves in thenon-flooded irrigation treaments suffered from both water stress and photo-inhibition atgrain-filling stage under unsaturated soil moisture content. The effects of stress and inhibition factors on photosynthetic apparatus increased as soil water content decreased. The restricteddegree in the DI treatment was smaller than that in the FIM and FIN treatments whencompared with the CF treatment. Photo-inhibition occurred at lower soil water potential in theDI treatment than in the FIM and FIN treatments. The negative effects of water stress andphotoinhibition in the non-flooded irrigation treatments were completely eliminated when soilwater content reached saturated soil moisture content following supplementary irrigation inthe DI and FIM treatments, but not in the FIN treatment. The DI treatment had a higherphotosynthetic productivity than either the FIM treatment or the FIN treatment throughout theentire observation period. Thermal dissipation pathways play important roles inphoto-protective mechanisms in rice plants growing in the non-flooded irrigation conditions.(5) The growth and development of all plant organs (including aboveground andunderground parts) were limited after jointing in the non-flooded irrigation treatments, whichthe DI treatment, especially for cultivar Ninggeng28, was experienced slight limitationcompared with the CF treatment. In contrast, the growth of all plant organs was much lowerin the FIN treatment than in the CF treatment. The RLD and leaf dry weight were moresensitive to the non-flooded irrigation treatments than sheath and root dry weight in the FIMand FIN treatments. However, in the DI treatment, the RLD and sheath dry weight were moresensitive to the non-flooded irrigation treatments than leaf and root dry weight. Increasing theroot/shoot ratio and RLD in the20~40cm depth (RLD40) and decreasing specific root lengthat0~20cm soil layer were important mechanisms for helping the rice plants to adapt to thenon-flooded environmental stresses when the growth and development of all organs wererestricted. Cultivar Ninggeng28was more suitable for the non-flooed irrigation cultivationthan cultivar Xindao17in current ecotope.(6) The RLD clearly dominated the growth and development of leaf dry weight and sheathdry weight in the non-flooded irrigation treatments before flowering. However, after floweing,only RLD at the depth of0~20cm (RLD20) directly affected leaf senescence process andpanicle dry weight. Root activity at all growth stages, RLD at mid-tillering, RLD20at jointing,RLD20at flowering, leaf dry weight at jointing and grain-filling were all significantly andpositively correlated with the grain yield in the non-flooded irrigation treatments. Rootactivity at all growth stages, RLD20at flowering, leaf dry weight at jointing and grain-fillingwere dominant factors affecting yield formation in the non-flooded irrigation treatments. Inconclusion, the RLD20and root activity, especially from flowering to maturity, play importantroles in the regulation of plant growth, development, and yield formation.(7) Under the non-flooded irrigation treatments, a lower seed setting rate was mainlyrelevant to a great amount of empty grain than under the CF treatment. Meanwhile, the gradeof the filled grain was significantly reduced under the non-flooded irrigation treatments compared with the CF treatment. This was mainly caused by a reduction in photosyntheticproductivity during grain-filling and/or by an insufficient dry matter supply capacity fromsheath organ after15th days after anthesis to grain in the non-flooded irrigation treatments.The duration of grain filling was longer in the non-flooded irrigation treatments than in theCF treatment. However, the rate of grain filling was more rapid in the non-flood irrigationtreatments than in the CF treatments. Further analysis showed that relatively low grain weightand the relatively slow seed setting rate in the non-flooded irrigation treatments were mainlyattributed to a longer grain filling period and a reduction in the rate of grain filling in thesuperior spikelet. The grain filling process in the DI treatment was only slightly different fromthat in the CF treatment. The main reason was that in the DI treatment, increasing the mattertranslocation from sheath to grain compemsated for the decrease in photosynthesis duringgrain filling stage when suitable varieties and water regime were conducted (i.e. cultivarNinggeng28interact the DI treatments).(8) To improve grain yield and WUE in plastic film mulch with drip irrigation, thecritical supplementary irrigation threshold with-30KPa soil water potential was moreconducive for root, sheath, and leaf organs growth, tillering, and the effective panicles per unitarea than that with-10KPa and the CF treatment before panicle initiation. However, thecritical supplementary irrigation threshold should be held at a soil water potential of-10KPa.This condition can keep the number of spikelets per panicle, the seed setting rate, and thegrain weight at levels nears to those observed in the CF treatment and much higher than thosein the-30KPa treatments. Finally, the DI treatement in the water regime mentioned above hasslightly less than or sometimes greater grain-yield than the CF treatment, and WUE can be asmuch as2.5times higher in the DI treatment than in the CF treatment when suitable varietiesare used. Increasing the number of effective panicles per unit area in the DI treatment couldbalance the slight reductions in the number of spikelets per panicle, the seed setting rate, andthe grain weight in the DI treatement with the mentioned water regimes compared with theCF treatment.(9) In the DI treatment, rice was more sensitive to soil temperature than to soil watercontent before panicle initiation. However, after panicle initiation, rice was more sensitive tosoil water content than to soil temperature. The following plant characteristics were closelyrelated to high yield and high WUE in the DI treatment:1. high RLD0~20and root activity;2.the ratio of floret number to maximum leaf area (leaf area at anthesis) ratio per unit area(Floret/LAMax) and the ratio of filled-grain number to maximum leaf area ratio per unit area(FG/LAMax) were approximately0.9, and the ratio of grain weight to maximum leaf area perunit area (GW/LAMax) was approximately0.02;3. The number of effective tillering paniclesand the harvest index of tillering panicles were both high. These results showed that in this study area, the effects of the DI treatment were betterthan those of either the FIM or the FIN treatments. The grain yield in the DI treatmentreached9000Kg ha-1, which was more2%than that in the CF treatment. In addition, wateruse efficiency in the DI treatment was2.5times that in the CF treatment. In conclusion, theDI system provides an important reference for the cultivation of rice using non-floodirrigation methods in arid region. |
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