| Organic manure application has been neglected in recent years, reflecting the rapid replacementof this compound with synthetic fertilizer. Furthermore, massive chemical fertilizer input, plastic film wide application and high planting density have caused soil degradation and crop yield stagnation, particularly in semiarid region of China. The yield potential under organic manure combined with chemical fertilizer and planting density still has promotion space. Therefore, the exploration of the positive and restorative effect of organicmanure on the soil water-nutrient status, maize physiological-ecological growing traits and stable-sustainable productivity is urgently needed.Three field experiments were conducted at semi-arid region of Northwest China(on the Loess Plateau) for three aims as follow:(Ⅰ) A two-year field experiment of two maize(Zea mays L.) cultivars planted alone or mixed planting with two different densities to determine the difference of morphological traits and competitiveness between the two mixed maize cultivars, and its effects on grain yield and water use efficiency(WUE).(Ⅱ)Aimed for explanation the effect of organic manure and planting density on soil water-nutrients status, maize root growth, shoot development and plants water eco-physiological properties, finally on the maize stable and sustainable yield production. Field experiment was conducted at three plant densities combined with organic manure application from 2011 to 2014.(Ⅲ)Field studies were conducted in five consecutive seasons(2011-2015) based on the main conclusions from above two experiments, the impact of optimized chemical fertilization strategies and extra organic manure input on the sustainable production in maize, water cycle in SPAC(Soil-Plant-Atmosphere continumum) and the soil properties was determined. Seven treatments were arranged under four stand densities, correspondingly different fertilizer managements and extra organic manure input, finally, to verify our hypothesis that extra organic manure input combined with suitable planting density and optimaized-chemical fertilization strategies could improve soil water and nutrients use by maize plants, which able to be a assistance for single-plant biomass distribution, then for stable and sustainable maize yield and water use efficiency, the main results showed as:(1). Kr of both maize cultivars in a mixture increased and contributed more to soil water uptake compared to that in monoculture, which directly associated with the increase of RLD in 0-30 cm soil layer. Low root biomass with high shoot biomass, i.e., lower root-to-shoot ratio in the mixed system indicated that root redundant growth and inefficient resource utilization was decreased. Importantly, the fluctuant increase of yield(10-16%) and WUE(5-14%) in a mixture attributed to the mixed planting density and the improvement in maize plants growth and grains development.(2). Increasing mixed planting density resulted in interactive intensity aggravated with the significant increase in CR and A, showed as S16 > Z958. Population AYL was increased mainly because of AYL of S16 increase, especially at high mixed density, furthermore, when S16 mixed with Z958 at 75,000 plants ha-1, LER and AYL in population-level were increased and indicated a mixed advantage of land use and grains production. Finally, the interaction between two maize cultivars caused that the yields of Z958 and S16 increased by 6.5% and WUE by 12% averagely over two years. Z958 showed more flexible and adaptable root system and weaker competitiveness which could provide a solid ecological foundation for stable and sustainable yield production in high planting density.(3). When organic manure appliedinfour continuous years, soil structure and deeper SWC(50-150cm) uptake was improved in a semi-arid of China. The topsoil nutrient content at maturity stage as N, P and SOM were significantly increased by 25.1%, 198.3% and 41.0% over three years, respectively. The surplus of soil nutrients after maize harvested was efficiently saved and this played an important role for high yield production in the following season.(4). Based on the soil water-nutrient status was improved, soil environment was better for root growth as the significant increase of RLD in 0-40 cm soil layer which supported the increase of Kr and soil water uptake improving under extra organic manure input, correspondingly, stem sap flow rate(SFR) increased which predicted an efficient canopy transpiration and leaf water use. After that, the maize growth and biomass allocation into shoot and grains increased and supported by decrease in RSR and increase of HI. In conclusion, the WUE increased by 5-16%, and this increase was positively associated with continuous increase by 11-24% in grain yield, which reflected the improvement of soil water-nutrients status under organic manure, and guaranteed the sustainability of crop production.(5). Cultivation practices as SY-O and EY-O improved topsoil envirenment which ensured SOM, N and P increased sustainably, accompanying, soil water use in 100-150 cm depth increased significantly, meanwhile the stability and balance of soil water in 0-100 and below-150 cm soil layer were maintained efficiently in SY-O and EY-O.(6). Higher planting density, optimized chemical fertilization technologies combined with extra organic manure input in EY-O and SY-O, obtained RLD in 0-40 cm soil profile and total RSA increase with single-plant Kr increased during grain filling stage, however, RW in 0-100 cm soil layer was suppressed. Combined with the improvement of stem flow rate(SFR) in single-plant, we concluded that extra organic manure application increased water uptake by root and efficient transferring in shoot, which guaranteed the canopy requirement of water and nutrient. Consequently, LA and shoot biomass of single-plant in SY-O and EY-O increased which established a solid foundation for photosynthetic product and grains filling rate, and then adjusted biomass allocation into above- and belowground part, i.e. RSR decreased significantly in SY-O and EY-O. When the organic manure applied in consecutive years, RSR decreased in EY-O year to year, because of soil water-nutrients environment improved which allowed small root system and great shoot development.(7). Basic on the improvement of shoot growth, number of ears and grain number per m2 increased significantly in SY-O and EY-O, mean of grain yield and WUE increased by 75% and 71% averagely over five years compared with that in only chemical fertilizer use and lower planting density. Extra organic manure application mitigated unnecessary yield loss in high planting density and supplied a sustainable productivity in single-plant level and population-level, then provided a friend way for dry land farm management. Finally, organic manure increased grain yield stably among tested years in SY-O and EY-O. Finally, the systematic expression of EY-O can be a valuable reference for the stable increase in yield and WUE at semi-arid farming region, and then realizing a win-win event of grain yield increase with soil environment improving. |
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