渭北旱塬西部作物水肥产量耦合效应研究

通过在渭北旱塬西部长武塬区所进行的玉米水肥两因子五水平试验，就作物水肥产量耦合效应进行了研究。在给出玉米水－肥生产函数的基础上，推出了养分优化供应条件下玉米分生产函数，阐明了水肥供应坐标面上产量，耗水量与水分利用效率等值线分布特征，并应用水分生产弹性系数，以产量与水分利用效率为目标，探讨了作物水肥优化耦合区域及其几何特征。     

灌溉和尿素类型对玉米水分利用效率的影响

水分和氮素运筹是提高作物产量的重要措施。为了研究不同灌水条件下常规尿素和控释尿素用量对玉米各生育期土壤含水率、籽粒灌浆速率和水分利用效率的影响,该文选用了常规尿素和控释尿素2种类型,施N量各设75和 150 kg/hm2 2个水平,以不施氮为对照;水分设置全生育期不灌水、浇85 mm灌浆水2个水平,随机区组设计。结果表明：相同灌水条件和施氮水平下,与常规尿素相比,控释尿素处理0～140 cm土层土壤含水率在玉米小口期前较高,而收获期却较低,实现了土壤水分的“前贮后用”。相同灌水条件和施氮水平下,与常规尿素相比,控释尿素处理玉米籽粒灌浆速率、总水分利用效率和灌溉水增产效率均显著提高。增加施N量显著提高总水分利用效率和灌溉水增产效率。与不灌溉相比,灌溉降低了玉米的总水分利用效率,但提高了玉米籽粒灌浆速率和籽粒产量。与常规尿素相比,控释尿素与水分对总水分利用效率和灌溉水增产效率的耦合效应更显著,利于高产与水分高效利用的同步。进一步分析表明,土壤水分的“前贮后用”和较高的灌浆速率是控释尿素能提高玉米总水分利用效率和灌溉水增产效率的重要原因。这对半湿润地区玉米节水高产栽培有重要参考价值。     

栽培模式及施氮对冬小麦-夏玉米体系产量与水分利用效率的影响

通过位于陕西杨凌的为期6年的田间定位试验,研究了长期覆盖栽培(常规、垄沟、覆草及控水)及施氮量(N0、120、240 kg/hm2)对小麦-玉米轮作体系作物产量及水分利用效率的影响。结果表明,与常规模式相比,垄沟和覆草模式均显著增加了玉米子粒产量,对小麦子粒产量的影响未达显著水平,控水模式降低了玉米和小麦的产量。4种不同栽培模式对玉米-小麦6年总产量的贡献大小顺序为:垄沟覆草常规控水,差异达显著水平。垄沟模式显著提高了玉米和小麦的水分利用效率;覆草和控水模式显著提高了玉米的水分利用效率,对小麦水分利用效率的提高未达显著水平。不同栽培模式下,玉米和小麦的总水分利用效率的大小顺序为:垄沟覆草控水常规,差异达显著水平。与未施氮肥相比,施氮N 120和240 kg/hm2显著提高了玉米、小麦的产量和水分利用效率,但两施肥处理间产量和水分利用效率差异不显著。     

耕作方法对黄土高原旱作玉米产量和土壤水温特性的影响

全膜双垄沟播是黄土高原旱作玉米主要生产技术,但此技术的土壤耕作主要依赖传统耕作和旋耕,在形成犁底层的同时造成耕层变浅,影响玉米生长、产量形成以及土壤健康。本文以打破犁底层、改善土壤结构、提高黄土高原旱地玉米(Zea may L.)产量和有限降水资源利用效率为目标,布设大田定位试验,比较研究了深松耕、免耕、旋耕和传统耕作对旱地全膜双垄沟播玉米土壤水分、温度、土壤容重、产量以及水分利用效率的影响。结果表明:全膜双垄覆盖条件下,深松耕和免耕较旋耕和传统翻耕能有效增加0~30 cm土壤贮水量,其0~30 cm土层土壤含水量较翻耕、旋耕分别增加50.0%、43.7%和14.8%、10.3%;深松耕能有效降低5~30cm土层土壤容重,其5~10 cm和10~30 cm土层土壤容重,深松耕较传统耕作分别降低10.9%和12.9%,随着土层的加深,深松耕、免耕的土壤容重呈降低趋势,旋耕和传统翻耕呈增大趋势;深松耕在苗期、拔节—抽雄期较传统翻耕分别具有明显的增温和降温作用,有利于玉米生长和产量提高;2个平水年,深松耕处理的玉米生物产量、籽粒产量和水分利用效率分别较传统翻耕增加6.1%~5.6%、18.6%~28.8%和28.1%~32.9%,具有明显的增产和提高水分利用效率的作用。因此,在黄土高原半干旱区同等降雨条件下,深松耕能有效增加全膜双垄沟播玉米的土壤贮水量,改善土壤结构,协调水温关系,有利于增产和提高水分利用效率,是全膜双垄沟播玉米一项理想的土壤耕作方法。     

基于通量观测数据的玉米水碳交换量及水分利用效率分析

揭示玉米生长期内水分、二氧化碳交换量及水分利用效率的变化规律,对于认识玉米生长规律,指导农业灌溉具有重要意义。该文采用美洲通量网(Ameri Flux)3个农田通量站的数据,计算玉米生育期内的水分消耗量ET(evapotranspiration)、总初级生产力GPP(gross primary productivity)和生态系统净交换量NEE(net ecosystem exchange)及水分利用效率,并采用统计分析方法分析饱和水汽压差和光合有效辐射对水分利用效率的影响。结果表明,该区域玉米整个生育周期约为156~180 d,ET为440~520 mm,GPP为1 320~1 640 g/m2,以C计,NEE为-560~-620 g/m2,以C计;水分利用效率,NEE/ET为1.2~1.4 g/kg,GPP/ET为3.0~3.5 g/kg。水分利用效率与饱和水汽压差(VPD)成负指数关系,存在常数k使得GPP/ET正比于VPD-k,最优k值为0.42~0.63。水分利用效率与光合有效辐射无显著相关性。     

茬口和灌水对小麦产量及水分利用效率的影响

为高效利用水分资源以及不同茬口冬小麦栽培提供合理的灌水制度,在山西临汾采用小区试验设计方法研究了茬口和灌水对小麦产量及水分利用效率的影响.结果表明:各茬口3个灌水处理的小麦平均产量以玉米茬口＞油葵茬口＞休闲茬口＞大豆茬口,水分利用效率则为油葵茬口＞玉米茬口＞大豆茬口＞休闲茬口;各茬口均随灌水量的增加产量和水分利用效率提高,大豆茬口的灌浆水、其他3个茬口的拔节水分别较拔节水、灌浆水更有利于提高小麦产量和水分利用效率.同时明确了不同灌水处理条件下,各茬口在不同生育时段贮水和耗水的动态特征.     

不同水分条件和覆盖处理对夏玉米籽粒灌浆特性和产量的影响

采用二因素完全随机试验设计,研究了3种水分条件(75%、65%、55%田间持水量)下无覆盖(CK)、地膜覆盖(PM)和秸秆覆盖(SM)处理对夏玉米籽粒灌浆特性、产量、耗水量及水分利用效率的影响。结果表明,不同水分条件下,各处理夏玉米籽粒增重进程符合Logistic生长曲线。相对于无覆盖处理,地膜和秸秆覆盖处理提高了夏玉米的灌浆速率、产量和水分利用效率。其中,中水分(65%田间持水量)条件下地膜和秸秆覆盖处理夏玉米产量及水分利用效率(WUE)增幅最大,增产率分别为21.99%和35.86%,水分利用效率增加幅度分别为16.41%和16.79%;其次为低水分(55%田间持水量)处理,高水分(75%田间持水量)处理增幅最小。     

不同覆盖对夏玉米叶片光合和水分利用效率日变化的影响

在中国气象局农业气象试验基地,对留残茬和秸秆覆盖措施下夏玉米叶片光合作用和叶片水平上的水分利用效率进行了试验研究,以探索夏玉米在这两种方式下的节水抗旱高产的生理生态机制。试验结果表明:光合速率日变化差异主要表现在上午;下午虽不甚明显,但也是覆盖和残茬两个处理略高于对照,说明2种土表覆盖方式促进了该时段光合速率的提高。留残茬和覆盖能明显提高夏玉米叶片水平上的水分利用效率,尤其在下午表现更为明显,最终提高产量水平上的水分利用效率,使农田的光、温和水资源得以科学有效地利用。     

旱地玉米水分高效利用平衡施肥技术的试验研究

通过６年田间试验研究,探讨平衡施肥技术对旱地玉米水分利用的影响。结果表明,在晋东豫西半湿润偏旱区,采用适宜的肥料品种、适宜的肥料用量、适宜的施肥时期以及适宜的施肥培肥方式方法,即采用平衡施肥技术有利于旱地玉米水分利用效率的提高,同时,可培肥土壤、保蓄土壤水分,促进旱地玉米对水分的充分利用     

耕作与施肥对旱地玉米田土壤耗水量和水分利用效率的影响

为探究保护性耕作与施肥对渭北旱地春玉米田土壤耗水量和水分利用效率的影响,达到高效生产的目的。于2013—2015年在渭北旱塬实施了春玉米耕作与施肥田间试验,共设置6种耕作与施肥处理:翻耕+低肥(A1)、免耕+高肥(A2)、深松+平衡施肥(A3)、翻耕+无肥(B1)、免耕+无肥(B2)和深松+无肥(B3),测定了春玉米休闲期与生育时期0~200 cm土层土壤蓄水量和收获时籽粒产量。结果表明:1)保护性耕作能显著提高旱地玉米田土壤蓄水保墒能力。与传统翻耕处理B1相比,休闲期,B2和B3播前土壤蓄水量分别提高23.39 mm和27.73 mm(P0.05);耕作处理区,B2和B3全生育期土壤蓄水量平均提高13.41 mm和15.70 mm;耕作施肥处理区,A2、A3土壤蓄水量较A1分别提高13.15 mm、19.54 mm。2)平衡施肥能有效提高玉米全生育期平均土壤蓄水量,与不施肥处理相比,全生育期土壤蓄水量平均提高6.79 mm(P0.05)。3)保护性耕作与施肥能提高玉米籽粒产量与水分利用效率。耕作无肥处理区,与B1比较,B3处理产量提高212~576 kg×hm~(-2),水分利用效率提高0.83~2.21 kg×hm~(-2)×mm~(-1);耕作施肥处理区,A3产量与水分利用效率提高最为显著,产量较A1提高659~1 495 kg×hm~(-2),水分利用效率提高0.65~3.82 kg×hm~(-2)×mm~(-1)(P0.05)。3种施肥方式下以氮、磷、钾平衡施肥产量与水分利用效率提高幅度最大。4)对耗水量与产量进行相关性分析发现,抽雄—灌浆生育阶段土壤耗水量与产量呈显著正相关,保护性耕作提高玉米生长初期土壤蓄水保墒能力,提高春玉米抽雄—灌浆期土壤水分,增加作物生长关键时期对水分的利用效率,利于玉米籽粒产量的提高。因此在渭北旱地春玉米田,深松与平衡施肥组合能提高春玉米产量与水分利用效率,是该地区玉米高效生产较为适宜的种植模式。     

Effect of Moisture Content on the Viscoelastic Properties of Individual Wheat Kernels Evaluated by the Uniaxial Compression Test Under Small Strain

Wheat product quality is related to its physicochemical properties and to the viscoelastic properties of the kernel. The aim of this work was to evaluate the viscoelastic properties of individual wheat kernels using the uniaxial compression test under small strain (3%) to create experimental conditions that allow the use of the elasticity theory to explain the wheat kernel viscoelasticity and its relationships to physicochemical characteristics, such as weight tests, size, and ash and protein contents. The following viscoelastic properties of the kernels of hard and soft wheat cultivars at two different moisture contents (original and tempered at 15%) were evaluated: total work (W_t), elastic work (W_e), plastic work (W_p), and modulus of elasticity (E). There was a significant decrease in W_t as the moisture content increased. In the soft wheat Saturno, W_t decreased 80% (from 0.217 to 0.044 N·mm) as the moisture content increased. Individual wheat kernels at their original moisture content showed higher W_e than under the tempered condition. W_p increased as the moisture content increased. E decreased as the moisture content increased. The soft wheat Saturno showed the highest decline (54.9%) in E (from 14.18 to 6.39 MPa) as the moisture content increased. There were significant negative relationships between the viscoelastic properties and the 1,000‐kernel weight and kernel thickness. The uniaxial compression test under small strain can be applied to evaluate the viscoelastic properties of individual wheat kernels from different classes and cultivars.     

耕作方式和秸杆还田对纤维素降解细菌多样性的影响

免耕和秸秆还田是培肥地力的重要措施,明确其对土壤纤维素降解细菌群落的影响对于土壤质量提升具有重要意义。选择中国科学院封丘农业生态国家试验站耕作秸秆还田(WtS)、免耕秸秆还田(WntS)、耕作秸秆不还田(Wt)和免耕秸秆不还田(Wnt)4种处理小区并采集土壤样品,用CMC-Na刚果红培养基对纤维素降解细菌计数,采用PCR-RFLP技术研究保护性耕作和秸秆还田对纤维素降解细菌群落的影响。结果表明,秸秆还田与免耕处理均不同程度提高了纤维素降解细菌数量。WtS、WntS、Wt和Wnt4个纤维素降解细菌基因文库中,OTUs数量分别为23、26、20和19个,秸秆还田加免耕处理多样性指数最高。本文获得的纤维素降解细菌共属于11个属,秸秆还田土壤中Streptomycetaceae、Flavobacterium、Sphingobium相对丰度明显多于秸秆不还田处理土壤;免耕处理土壤中Pseudomonas、Phyllobacterium、Paenibacillus、Promicromonosporaceae、Sphingobacterium相对丰度明显高于耕作处理土壤。典范对应分析显示四种处理纤维素降解细菌群落结构发生了较大变化,p H、全磷、有机碳和全钾与免耕处理呈显著正相关性,全氮、碱解氮、速效钾、速效磷和有机碳与秸秆还田处理呈显著正相关性。免耕和秸秆还田能提高土壤中纤维素降解细菌数量及多样性,改变纤维素降解细菌群落结构。     

时空亏缺调控灌溉和施氮处理对番茄水氮利用的影响

为探索节水灌溉条件下蔬菜的水肥高效利用模式, 采用番茄盆栽试验, 以常规充分灌水为对照, 研究了时空亏缺调控灌溉和氮肥处理对番茄营养器官干物质累积、灌溉水分利用效率、氮素累积及土壤水氮分布的影响。在交替灌溉条件下, 设置控水时期、灌水水平和施氮水平3因素, 控水时期分别为开花座果期和结果期, 2个灌水水平分别为高水和低水, 3个施氮水平分别为高氮、低氮和无氮, 并以常规灌溉作为对照。结果表明: 与常规充分灌水处理相比, 交替灌溉持续高水处理、交替灌溉开花座果期低水处理、交替灌溉结果期低水处理及交替灌溉持续低水处理分别降低干物质累积总量4.52%、11.93%、17.76%和23.94%, 分别降低氮素累积总量1.74%、12.86%、15.50%和22.47%, 分别降低氮素干物质生产效率2.24%、3.93%、2.55%和0.89%, 而分别增加灌溉水分利用效率12.39%、8.99%、15.02%和12.96%。在交替灌溉条件下, 中氮处理的干物质累积、灌溉水分利用效率和氮素累积总量最大。与低氮处理相比, 中氮和高氮处理的氮素干物质生产效率分别降低6.87%~12.70%和17.81%~24.38%, 土壤硝态氮分别提高31.64%~159.58%和57.37%~297.37%。综合考虑干物质累积、水分利用及氮素累积等因素, 番茄适宜的水氮供给模式为交替灌溉持续高水中氮处理: 灌水定额为80%W₀(W₀为常规充分灌溉的灌水定额, 保持土壤含水量为田间持水量的70%~85%), 施氮量为0.30 g(N)·kg^-1(干土)。     

水磷耦合烤烟养分吸收分配规律研究

为探究烤烟适宜的水磷耦合模式及其对氮、磷、钾养分吸收积累的影响。采用田间小区试验,试验设置3种灌水水平和施磷水平,分别为低水(W_1:0.50 L/株)、中水(W_2:1.00 L/株)、高水(W_3:2.00 L/株)和低磷(P_1:32 kg/hm^2)、中磷(P_2:64 kg/hm^2)、高磷(P_3:96 kg/hm^2),研究了不同施磷量和灌水量条件下烤烟对氮磷钾养分吸收积累的影响。结果表明:施磷量相同时,灌水处理能够明显增加烟株对氮、磷、钾养分的吸收积累量,表现为:W_3P_i>W_2P_i>W_1P_i>CK_i(其中i=1或2或3);当灌水量相同时,增加施磷量也有利于烟株对氮磷钾养分的吸收积累,且在施磷水平为96 kg/hm^2时表现较好,表现为:W_iP_3>W_iP_2>W_iP_1;高磷水平下,灌水量为1.00,2.00 L/株时,W_3P_3和W_2P_3处理烟株对氮磷钾养分的吸收积累量差异不显著;烟株和根、茎、叶各器官对钾的吸收量高于氮和磷,氮、磷、钾在根、茎、叶器官中的分配顺序呈现叶>茎>根的变化规律;在烟株的不同生育期,对养分的吸收积累量和积累强度存在差异。烟株对养分的吸收积累主要在旺长期,烟叶是养分的主要吸收积累器官;施磷量为96 kg/hm^2,灌水量为1.00～2.00 L/株的水磷耦合处理在促进烟株对氮磷钾养分的吸收积累方面效果较好。烤烟施肥中要注意调整氮磷钾的施用比例和水磷耦合配比。     

成都平原两熟区水氮管理模式与磷钾肥配施对杂交稻冈优725产量及品质的影响

以杂交稻冈优725为材料,通过淹水灌溉+氮肥优化运筹（W1N1）、 控制性交替灌溉+氮肥优化运筹（W2N1）、 旱种+氮肥优化运筹（W3N2）3 种水氮管理模式及不同的磷钾肥配施处理,研究其对成都平原两熟区水稻产量、 养分分配及品质的影响。结果表明,水氮管理模式和磷钾肥配施对稻米品质、 稻株各营养器官养分分配及产量均存在显著影响;水氮管理模式对稻谷产量、 整精米率、 直链淀粉、 蛋白质及RVA谱影响明显高于磷钾配施处理,而磷钾肥配施对垩白度、 垩白粒率、 胶稠度的调控作用显著。W2N1相对于W1N1及W3N2水氮管理模式的水稻产量分别提高3.02%和28.21%,为本试验最优的水氮管理模式,且与施磷量P2O5 90 kg/hm2、 施钾量K2O 90~180 kg/hm2 配施组合能进一步提高结实率和千粒重,利于成熟期籽粒氮、 磷、 钾素及稻株总养分累积量的增加,达到水肥耦合促产的目的,而且能提高整精米率、 胶稠度、 蛋白质含量,降低垩白度、 垩白粒率、 直链淀粉及消减值,改善米质。W1N1模式与P90K90配施为宜;旱种相对于淹灌下的水氮优化管理模式,不利于产量及米质的提高,但与P90K180配合对稻谷的产出及米质的改善有一定的补偿作用,可为生产中在水资源不足的情况下提供参考。     

Effect of post‐methanation effluent on soil physical properties under a soybean‐wheat system in a Vertisol

Post‐methanation effluent (PME) generated through bio‐methanation of distillery effluent, a foul‐smelling, dark colored by‐product of distillery industries, is applied to arable land in some areas near the vicinity of the distillery industries as an amendment. The PME contains considerable amount of organic matter and salt besides its high plant‐nutrient content. The present investigation was conducted for three years during 1999–2002 on soybean‐wheat cropping sequence to evaluate the effect of graded levels of post‐methanation effluent (PME) on soil physical properties and crop productivity in a deep Vertisol of central India. Six application doses of PME viz. S_2.5+W₀: 2.5 cm PME applied to soybean and wheat on residual nutrition, S_2.5+W_1.25: 2.5 cm PME to soybean and 1.25 cm to wheat, S_5.0+W₀: 5 cm PME to soybean and wheat on residual nutrition, S_5.0+W_2.5: 5.0 cm PME to soybean and 2.5 cm to wheat, S_10.0+W₀: 10 cm PME to soybean and wheat on residual nutrition, and S_10.0+W_5.0: 10.0 cm PME to soybean and 5.0 cm to wheat, were compared with 100% recommended NPK+FYM ? 4 Mg ha^–1 and control (no fertilizer, manure or PME). The application of PME increased the organic carbon content and electrical conductivity of the soil compared to control and 100% NPK+FYM treatment. The organic C content was maximum in S_10.0+W_5.0 (11.2 g kg^–1) and minimum in control (5.2 g kg^–1). Electrical conductivity increased from 0.47 dS m^–1 in control to 1.58 dS m^–1 in highest dose of PME (S_10.0+W_5.0). The PME treatments have not affected the soil pH. The application of PME showed a significant improvement in the physical properties of the soil. The mean weight diameter (MWD), percent water‐stable aggregation (% WSA), saturated hydraulic conductivity (K_sat), and water retention (WR) at 0.033 MPa suction were significantly (P < 0.05) more while bulk density (BD) and penetration resistance was significantly less in PME‐treated plots than that of control. The MWD showed a linear and positive relationship (r = 0.89**) with the soil organic C. Soybean recorded significantly higher seed yield at all PME treatments than control. Highest average soybean yield (2.39 Mg ha^–1) was recorded in S_10.0+W₀ but yield decreased significantly in S_10.0+W_5.0 (2.08 Mg ha^–1). In wheat, all the PME‐treated plots except S_2.5+W₀ yielded significantly higher than control while the 100% NPK+FYM treatment yielded (3.46 Mg ha^–1) at par with the S_10.0+W_5.0 (4.0 Mg ha^–1) and S_5.0+W_2.5 (3.66 Mg ha^–1). Fresh application of PME to wheat resulted in significant improvement in grain yield over that grown on residual fertility. Thus, application of PME to arable land, as an amendment, could be considered as a viable option for the safe disposal of this industrial waste.     

Soil Respiration Characteristics in Three Shrublands along an Elevation Gradient in a Semiarid Loess Plateau Mountain Area

Shrub is one of the major vegetation types distributed mostly in the mountainous area in China, and its vegetation carbon storage is approximately one-third of both forests and grasslands. It is essential to investigate how soil temperature (T_s) and soil water content (W_s) affect soil respiration (R_s) in this ecosystem. The purpose of this study was to understand the correlations of R_s with T_s, W_s, and other factors in the shrubs. In the current study, R_s was characterized in three shrublands (hereafter, shrub 1, shrub 2, and shrub 3, respectively) located in different elevations over a 4-year period at a biweekly interval in the eastern Loess Plateau (Shanxi province) of China. Our results showed that the trend of seasonal change of R_s was controlled mainly by T_s and W_s. The measured mean R_s over 4 years was 3.64 ± 2.83 (mean ± S.D.), 2.69 ± 2.05, and 4.41 ± 3.28 μmol carbon dioxide (CO₂) m^?2 s^?1 for shrubs 1, 2, and 3, respectively, exhibiting an increase trend with elevation increment. Over the season, R_s illustrated a significant change depending on the variation of T_s and W_s, with larger values appearing in summer when both T_s and W_s were high, and smaller values in winter or in summer whenever W_s was low. An exponential model (R_s = a e ^bTs) fitted well the relation between R_s and T_s for shrub 3, whereas linear (R_s = a W_s + b) and power (R_s = a W_s ^b) models of R_s to W_s fitted well for shrub 1. This indicated that at a lower elevation, W_s had a greater effect on R_s than that at a higher elevation. The reverse trend was true between R_s and T_s, i.e., at a higher elevation T_s had a greater effect on R_s than that at a lower elevation. The calculated Q₁₀ values of 1.61, 3.03, and 3.73 for shrubs 1, 2, and 3 increased to 2.25, 3.63, and 4.07, respectively (when the data in low W_s conditions were excluded from the analysis), showing that Q₁₀ increased with elevation increment. Furthermore, three two-variable models, one linear (R_s = a (T_s W_s) + b), and two nonlinear (R_s = a T_s ^b W_s ^c and R_s = a e^bTs W_s ^c), were also well developed to predict the dependency of R_s on both T_s and W_s. Our research results might have important implications for the estimation of soil carbon emissions of the shrublands in this region.     

Response of cotton root growth and yield to root restriction under various water and nitrogen regimes

Water and nitrogen (N) are two major factors limiting cotton growth and yield. The ability of plants to absorb water and nutrients is closely related to the size of the root system and the rooting space. Better understanding of the physiological mechanisms by which cotton (Gossypium hirsutum L.) adapts to water and N supply when rooting volume is restricted would be useful for improving cotton yield. In this study, cotton was grown in soil columns to control rooting depth to either 60 cm (root‐restriction treatment) or 120 cm (no‐root‐restriction treatment). Four water–N combinations were applied to the plants: (1) deficit irrigation and no N fertilizer (W₀N₀), (2) deficit irrigation and moderate N fertilizer rate (W₀N₁), (3) moderate irrigation and no N fertilizer (W₁N₀), and (4) moderate irrigation and moderate N fertilizer rate (W₁N₁). Results revealed that root restriction reduced root length density (RLD), root volume density (RVD), root mass density (RMD), superoxide dismutase (SOD) activity, nitrate reductase (NR) activity, total plant biomass, and root : shoot ratio. In contrast, root restriction increased aboveground biomass and yield. The RLD, RVD, RMD, and root : shoot ratio decreased in the order W₀N₀ > W₁N₀ > W₀N₁ > W₁N₁ in both the root‐restriction and no‐root‐restriction treatments. However, the opposite order (i.e., W₁N₁ > W₀N₁ > W₁N₀ > W₀N₀) was observed for SOD activity, NR activity, aboveground biomass, and seed yield. Our results suggest that, when N and water supplies are adequate, root restriction increases both root activity and the availability of photosynthates to aboveground plant parts. This increases shoot growth, the shoot : root ratio, and yield.     

Einfluß von Bewässerung und Plazierung von markierten Stickstoff-Düngern auf Ertrag und Stickstoffentzug bei Weizen unter semiariden Klimabedingungen im Iran

Effect of Irrigation and Fertilizer Placement on the N-Uptake by Wheat under Semiarid Conditions of Karadj/Iran Field and greenhouse experiments were conducted under semiarid conditions of Karadj/Iran on a sandy to silty loam of alluvial soils (pH% 8,2) to study the effects of soil moisture regimes and N-fertilizer placement on yield, N-uptake and recovery of fertilizer N from ¹⁵NH₄ ¹⁵NO₃, (¹⁵NH₂)₂CO and (¹⁵NH₄)₂SO₄. There were two moisture regimes as main plots (W₁ = Irrigation at 50% and W₂ = Irrigation at 25% available water in 0–30 cm depth of soil), and two methods of fertilizer placement (broadcast and band application). Irrigation at (W₁) increased the grain and straw yield 11 and 19% but not total N-uptake in the field experiment. (W₁)-irrigation combined with band application resulted in the highest yield and total N-uptake. Utilization of applied N, however, was higher with (W₂)-irrigation in both fertilizer placements. This result was confirmed by the data of the greenhouse experiment. Band application was superior to broadcast application for fertilizer N-uptake with both water managements. Ammonium sulfate showed the highest and urea the lowest difference between the two fertilizer placements.     

Enhancement of Depleted Loam Soil as Well as Cucumber Productivity Utilizing Biochar Under Water Stress

Biochar has recently received increased attention because it improves poor soil fertility. However, its potentiality to enhance soil physical properties under water stress conditions not yet deeply investigated. Hence, extensive field investigations were carried out to study the effects of biochar addition (BA) with deficit irrigation (DI) on soil bulk density (BD), porosity percentage (P%), soil moisture content (SMC%), soil hydraulic conductivity (K), cucumber yield and water use efficiency (WUE) during two consecutive seasons (2016 and 2017). The biochar treatments were B₀ (0 ton ha^?1), B₁ (10 ton ha^?1and B₂ (20 ton ha^?1), while the DI treatments were 1.0 (W₁), 0.60 (W₂) and 0.40 (W₃) of the reference evapotranspiration (ET₀). The parameters were measured at soil depths of 0–10 (d₁), 10–20 (d₂) and 20–30 cm (d₃) for measurement periods of before sowing (P₁), mid-season (P₂) and after harvest (P₃). The results showed that the B₂W₁ combination gave the highest yield (57 and 45.2 t ha^?1), WUE (10.94 and 11.27 kg m^?3), SMC (39.2 and 40.1%) in both seasons, respectively. The B₂W₃ had the highest porosity (47.5 and 46.1%) values at the d₁. Meanwhile, the lowest soil BD values of 1.1 and 1.05 g cm^?3 were obtained by the B₂W₁ at d₁ for 2.16 and 2017, respectively. Statistically, most of the parameters studied under B₂W₂ and B₀W₁ had non-significant differences between them. Hence, the addition of biochar with DI could be an integrated approach to address the drought stress, while enhancing soil and plant properties.