沟灌水氮耦合对毛白杨林木生长及水氮吸收利用的影响

为探索沟灌水氮耦合对幼年生毛白杨林木生长及水氮吸收利用的影响,以4年生砂地三倍体毛白杨为对象,研究3个灌溉水平(W20、W33、W45,即沟渠正下方40 cm土壤水势分别达到-20、-33和-45 kPa时灌溉),4个施N水平(N120、N190、N260、N0,即施肥量为120、190、260和0 kg·hm^-2·a-1)和自然条件(对照,CK)下幼年生毛白杨林木生长和水氮吸收利用规律,并结合林木生长状况,分析4年生三倍体毛白杨的最佳沟灌水氮耦合策略。结果表明:W20N120(高水低肥;土壤水势-20 kPa,施N量120 kg·hm^-2·a-1)处理对三倍体毛白杨的林地生产力提升最为显著,其林地生产力最高可达33.37 m3·hm^-2·a-1,仅有树高和总株生物量受到水氮耦合交互作用的显著影响。增加灌溉量或施N量都会提高林木吸氮量,但吸氮量主要受施N量影响;W20N260处理总株吸氮量最高,达112.17 kg·hm^-2·a-1,较CK增加74.0%。各处理中,W20N120氮吸收效率和氮肥偏生产力最高,且显著高于其他处理,其总株、地上部、地下部氮吸收效率可达36.8%、28.5%、6.4%,总株氮肥偏生产力可达221.4 kg·kg^-1。不同水氮耦合处理灌水量对灌溉水的利用效率影响显著,其中,W45N260灌溉水利用效率最高,达13.66 g·kg^-1;而W20N120吸水量和水吸收效率最高,分别为13268.28 t·hm^-2和129.4%。为达到较大的收益,在三倍体毛白杨的幼年生长期间,应保持充足的水分灌溉(-20 kPa)和相对偏低的施氮量(120 kg·hm^-2·a-1)促进幼年生毛白杨的生长发育。

优质樱桃番茄高效水氮耦合管理

【目的】水分和氮素是限制作物产量和品质的最重要因素,合理的水肥管理是农业生产高产高效的关键。结合同位素技术研究最优水氮耦合模式,为樱桃番茄生产中合理灌水和施氮,提高番茄果实品质及水分利用效率(WUE)提供科学依据。【方法】以樱桃番茄品种‘千禧’为试验材料,结合稳定同位素技术进行水肥耦合盆栽试验。试验设置3个灌溉水平(W)和3个氮素水平(N),灌溉水平包括90%土壤持水量(充分供水,WH),70%土壤持水量(中度水分胁迫,WM)和50%土壤持水量(重度水分胁迫,WL);氮素水平包括高氮(0.23 g/kg,NH),中氮(0.16 g/kg,NM)和低氮(0.08 g/kg,NL)。试验采用完全随机设计,共9个处理。在灌溉施肥处理60天后收获,分析测定了植株不同部位的生物量及碳、氮、氧同位素含量。【结果】在WH和WM条件下,增加氮素用量使番茄地上部干物质量和叶面积显著增加,增幅分别为19.8%~45.4%和29.4%~106.8%;相同氮素水平下,WH和WM的地上部干物质量和叶面积比WL分别增加24.7%~83.4%和17.6%~90.4%。WHNH处理干物质量和叶面积最高,WMNH处理次之,但后者耗水量低,具有最高的WUE。在WH和WM下,随着氮素用量的增加番茄植株的WUE和氮素含量同步增加。土壤水分水平下降提高了植株的WUE以及δ13C和δ18O,而WUE提高的主要原因是由于叶片气孔的优化调控,植株叶片的δ13C和δ18O可以用于表示灌溉施肥条件下长时间尺度上的WUE信息。WLNM处理提高番茄的糖分含量,而WHNM处理能降低番茄的有机酸含量,从而使番茄口感更好,提高番茄品质。【结论】中度水分胁迫和高氮处理(WMNH)能在促进番茄生长和提高氮素吸收和利用效率的同时减少水分用量,提高番茄的水分利用效率,为本试验的最优水氮耦合处理。

水肥耦合对杨树根区水、氮运移及吸收的影响研究进展

随着我国木材需求量不断增加,速生丰产林提质增产迫在眉睫,急需探求合理高效的水肥集约经营策略。文中对灌溉施肥条件下植物根区水和氮(N)运移分布、吸收根形态与分布,以及水和N吸收相关研究进行综述,结论如下:1)水、N分布与施肥灌水量、土壤质地、降水、地下水位等条件有关。主要研究方法有室内、大田试验以及数值模拟法。由不同时刻水、N运移分布情况发现,改善水肥耦合措施,可降低N淋失对地下水的污染,同时提高植物的水、N利用效率。2)杨树吸收根主要分布于土壤表层,呈"倒金字塔"型分布,随远离树干方向,分布趋于浅层化,垂直根呈"S"形,整体表现为"二态性";从根系分布规律发现,少量多次随水施肥有利于吸收根及林分生长。3)杨树品种、生育阶段、施肥水平以及土壤条件等不同,其水、N吸收情况及后期分配均存在差异。但恰当的水肥比例和灌施频率均有利于水、N吸收。以往研究只关注根区水和N运移、根系分布、吸收利用过程中的某一环节,而对各环节间动态联系以及整体调控机制知之甚少。因此,应设置不同水、N耦合方式,对各环节进行关联分析,明确调控机制,以期实现水、N效率最大化,有效提升林木产量。

Effect of Transplanting Density on Rice Yield,Nitrogen Uptake and ^(15)N-fertilizer Fate

[Objective] The aim of this study was investigated the rice yield, nitrogen uptake and ^15-fertilizer fate at different transplanting density to provide scientific ba- sis for improving the yield of rice and applying reasonably fertilizer. [Method] A field experiment was carried out to study the effect of different transplanting density on rice yield, nitrogen （N） absorption, sources of N uptake by rice and the N balance in the plant-soil systems by using ^15-labelled urea. [Result] There were no significant differences in rice yields and total N uptakes by rice between treatments 30 cm × 30 cm and 40 cm × 40 cm, but the yield of rice and total N absorption in the two treatments were remarkably higher than those in 50 cm × 50 cm treatment. The amounts of total N uptake by rice were in the range of 112.3-162.7 kg/hm2 in the three transplanting densities. The result showed that about 1/3 of the total N uptake by rice was supplied by application fertilizer and the other 2/3 was obtained from the soil N pool. The ^15N-labelled urea absorbed by rice, residual in soil and lost accounted for 16.3%-26.1%, 17.0%-20.9% and 53.0%-66.7% of the total fertilizer, respectively. A great deal of ^15N-labelled urea was lost during the rice growing season. [Conclusion] Considering the rice yield and environmental protection, the transplanting density of 30 cm×30 cm was recommended in the hilly area of Sichuan basin in the southwest China.

Effects of Atmospheric CO_2 Enrichment, Applied Nitrogen and Soil Moisture on Dry Matter Accumulation and Nitrogen Uptake in Spring Wheat

Spring wheat (Triticum aestivum L. cv. Dingxi No. 8654) was treated with twoconcentrations of atmospheric CO_2 (350 and 700 μmol mol^(-1)), two levels of soil moisture(well-watered and drought) and five rates of nitrogen fertilizer (0, 50, 100, 150, and 200 mgkg^(-1) soil) to study the atmospheric CO_2 concentration effect on dry matter accumulation and Nuptake of spring wheat. The effects of CO_2 enrichment on the shoot and total mass depended largelyon soil nitrogen level, and the shoot and total mass increased significantly in the moderate to highN treatments but did not increase significantly in the low N treatment. Enriched CO_2 concentrationdid not increase more shoot and total mass in the drought treatment than in the well-wateredtreatment. Thus, elevated CO_2 did not ameliorate the depressive effects of drought and nitrogenstress. In addition, root mass decreased slightly and root/shoot ratio decreased significantly dueto CO_2 enrichment in no N treatment under well-watered condition. Enriched CO_2 decreased shoot Ncontent and shoot and total N uptake; but it reduced root N content and uptake slightly. Shootcritical N concentration was lower for spring wheat grown at 700 μmol mol^(-1) CO_2 than at 350μmol mol^(-1) CO_2 in both well-watered and drought treatments. The critical N concentrations were16 and 19 g kg^(-1) for the well-watered treatment and drought treatment at elevated CO_2 and 21 and26 g kg^(-1) at ambient CO_2, respectively. The reductions in the movement of nutrients to theplant roots through mass flow due to the enhancement in WUE (water use efficiency) and the increasein N use efficiency at elevated CO_2 could elucidate the reduction of shoot and root Nconcentrations.

Growth and Phosphorus Uptake of Oat (Avena nuda L.) as Affected by Mineral Nitrogen Forms Supplied in Hydroponics and Soil Culture

Plants show different growth responses to N sources supplied with either NH4^＋ or NO3^-. The uptake of different N sources also affects the rhizosphere pH and therefore the bioavallability of soil phosphorus, particularly in alkaline soils. The plant growth, P uptake, and P availability in the rhizosphere of oat （Arena nuda L.） grown in hydroponics and in soil culture were investigated under supply with sole NH4^＋-N, sole NO3-N, or a combination. Sole NO^- -fed oat plants accumulated more biomass than sole NH4^＋ -fed ones. The highest biomass accumulation was observed when N was supplied with both NH^＋ -N and NO3^- -N. Growth of the plant root increased with the proportion of NO3^- in the cultural medium. Better root growth and higher root/shoot ratio were consistently observed in NO3^- fed plants. However, root vigor was the highest when N was supplied with NO3^- ＋NH4^＋. NH4^＋ supply reduced the rhizosphere pH but did not affect P uptake by plants grown in soils with CaHPO4 added as P source. No P deficiency was observed, and plant P concentrations were generally above 2 g kg^-1. P uptake was increased when N was supplied partly or solely as NO3^--N, similarly as biomass accumulation. The results suggested that oat was an NO3-preferring plant, and NO3^- -N was essential for plant growth and the maintenance of root absorption capacity. N supply with NH4^＋ -N did not improve P nutrition, which was most likely due to the absence of P deficiency.

Relationships Between Yield, Quality and Nitrogen Uptake and Utilization of Organically Grown Rice Varieties

Due to the relatively late start of organic rice(Oryza sativa L.) research in China,there is a still lack of systematic research on rice varieties,organic fertilizer management practices,and especially the mechanisms of nitrogen(N) uptake and utilization.Three rice varieties,Nanjing 5055,Nanjing 9108,and Nanjing 46,were grown under organic farming(OF) at three organic fertilizer levels(103.2,160.8,and 218.4 kg N ha^(-1)) and conventional farming(CF) with regular chemical fertilizers.Rice grain yields,yield components,and quality,dry matter accumulation,and plant N were measured at different growth stages during the 2012 and 2013 growing seasons.Compared with CF,OF had a significantly reduced yield.Nanjing 9108 showed significant reductions in number of panicles per unit area and percentage of filled grains,and had the lowest yield.The effects of fertilizer type and application rate on dry matter accumulation during the main growth periods were significant for all varieties.The N content and uptake in organically grown rice were lower compared with those of rice under CF.The N recovery efficiency and N agronomic efficiency were significantly lower,whereas N physiological efficiency and N partial factor productivity were greater under OF than under CF.Under OF,the processing quality showed a slight but insignificant decline,protein content and gel consistency increased,and amylose content decreased compared with those under CF.Correlation analysis showed that under OF,grain yield was significantly correlated with N uptake.The medium organic fertilizer level(160.8 kg N ha^(-1)) was found to be the optimum fertilizer treatment,and Nanjing 46 appeared to be the best variety for organic rice cultivation.To increase rice grain yields and reduce the potential risk of non-point source pollution in organic agriculture,further research is needed to improve the N use efficiency in organic rice cultivation.