Water use and water use efficiency of sweet corn under different weather conditions and soil moisture regimes

Plant growth and development are influenced by weather conditions that also affect water use (WU) and water use efficiency (WUE) and ultimately, yield. The overall goal of this study was to determine the impact of weather and soil moisture conditions on WU and WUE of sweet corn (Zea mays L. var rugosa). An experiment consisting on three planting dates was conducted in 2006 at The University of Georgia, USA. A sweet corn genotype sh2 was planted on March 27 under irrigated and rainfed conditions and on April 10 and 25 under irrigated conditions only. Soil moisture was monitored using PR2 probes. Rainfall and irrigation were recorded with rain gauges installed in the experimental area while other weather variables were recorded with an automatic weather station located nearby. A water balance was used to obtain the crop's daily evapotranspiration (ETc). WUE was calculated as the ratio of fresh and dry matter ear yield and cumulative ETc. The potential soil moisture deficit (Dp) approach was used to determine the crop's moisture stress. Results were analyzed using a single degree freedom contrast, linear regression, and the least significant difference. WU and WUE of sweet corn were both markedly affected by the intra-seasonal weather variability and Dp. For both variables, significant (p < 0.05) differences were found between planting dates under irrigated conditions and between the irrigated and rainfed treatments. WU was as high as 268 mm for the April 10 planting date under irrigated conditions and as low as 122 mm for the March 27 planting date under rainfed conditions. The maximum soil moisture deficit was reached at the milky kernel stage and was as high as 343 mm for the March 27 planting date under rainfed conditions and as low as 260 mm for the April 10 planting date under irrigated conditions. Further work should focus on the impact of the intra-seasonal weather variability and soil moisture conditions during different crop stages to determine critical periods that affect yield.     

Effects of irrigation regimes on the yield and water use of strawberry

Summary Strawberry plants (Fragaria x annanasa D. cv Chandler) were grown in field plots and in drainage lysimeters under controlled soil moisture regimes. Four irrigation treatments were established by watering the plants when soil water potential reached -0.01, -0.03,-0.05 and -0.07 MPa. The maximum yield was attained at -0.01 MPa soil water potential. Differences in yield were caused by both changes in the number of fruits per plant and in the fresh weight per fruit. Yield reductions were associated with reductions in total assimilation rate resulting from the decreased assimilatory surface area in plants irrigated at lower soil water potentials. The crop water production function calculated on a fruit fresh weight basis resulted in a yield response factor (K _y) of 1.01.     

Effect of soil matric potential on tomato yield and water use under drip irrigation condition

Field experiment was carried out to investigate the effect of soil matric potential (SMP) on tomato yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) under drip irrigation condition in North China Plain. The experiment included five treatments, which controlled SMP at 0.2 m depth immediately under drip emitter higher than −10 (S1), −20 (S2), −30 (S3), −40 (S4) and −50 kPa (S5), respectively, after tomato plant establishment. The results showed that different SMP affected irrigation amount and tomato ET. Irrigation amount decreased from 185 mm (S1) to 83.6 mm (S5) in 2004, and from 165 mm (S1) to 109 mm (S5) in 2005, respectively. The ET decreased from 270 mm (S1) to 202 mm (S5) in both years. However, it was found that SMP did not affect the tomato yield significantly, for the range of SMP investigated. Both WUE and IWUE increased as SMP decreased. The maximum WUE (253 and 217 kg/ha mm) and IWUE (620 and 406 kg/ha mm) were for S5 in 2 years, whereas the minimum WUE (178 and 155 kg/ha mm) and IWUE 261 and 259 kg/ha mm) were for S1 in 2004 and 2005. Based on the above results, therefore, it is recommended that if the tomatoes are well irrigated (SMP is higher than −20 kPa) during establishment, controlling SMP higher than −50 kPa at 0.2 m depth immediately under drip emitter can be used as an indicator for drip irrigation scheduling during following period of tomato growth in North China Plain.     

Effect of irrigation methods,management and salinity of irrigation water on tomato yield,soil moisture and salinity distribution

The increasing demand for irrigation water to secure food for growing populations with limited water supply suggests re-thinking the use of non-conventional water resources. The latter includes saline drainage water, brackish groundwater and treated waste water. The effects of using saline drainage water (electrical conductivity of 4.2–4.8 dS m⁻¹) to irrigate field-grown tomato (Lycopersicon esculentum Mill cv Floradade) using drip and furrow irrigation systems were evaluated, together with the distribution of soil moisture and salt. The saline water was either diluted to different salinity levels using fresh water (blended) or used cyclically with fresh water. The results of two seasons of study (2001 and 2002) showed that increasing salinity resulted in decreased leaf area index, plant dry weight, fruit total yield and individual fruit weight. In all cases, the growth parameters and yield as well as the water use efficiency were greater for drip irrigated tomato plants than furrow-irrigated plants. However, furrow irrigation produced higher individual fruit weight. The electrical conductivity of the soil solution (extracted 48 h after irrigation) showed greater fluctuations when cyclic water management was used compared to those plots irrigated with blended water. In both drip and furrow irrigation, measurements of soil moisture one day after irrigation, showed that soil moisture was higher at the top 20 cm layer and at the location of the irrigation water source; soil moisture was at a minimum in the root zone (20–40 cm layer), but showed a gradual increase at 40–60 and 60–90 cm and was stable at 90–120 cm depth. Soil water content decreased gradually as the distance from the irrigation water source increased. In addition, a few days after irrigation, the soil moisture content decreased, but the deficit was most pronounced in the surface layer. Soil salinity at the irrigation source was lower at a depth of 15 cm (surface layer) than that at 30 and 60 cm, and was minimal in deeper layers (i.e. 90 cm). Salinity increased as the distance from the irrigation source increased particularly in the surface layer. The results indicated that the salinity followed the water front. We concluded that the careful and efficient management of irrigation with saline water can leave the groundwater salinity levels unaffected and recommended the use of drip irrigation as the fruit yield per unit of water used was on average one-third higher than when using furrow irrigation.     

Grain yield and water use efficiency of two types of winter wheat cultivars under different water regimes

To improve grain yields of winter wheat and water-use efficiency in the water-shortage region of the North China Plain (NCP), field experiments involving three irrigation levels and two types of winter-wheat cultivars (Shijiazhuang 8 and Xifeng 20, with moderate and strongly drought tolerance, respectively) were conducted over three growing seasons with different levels of precipitation. The results showed that irrigation significantly improved the grain yield of both wheat cultivars. The response of grain yield was largest in the dry year, followed by the normal and wet years. Shijiazhuang 8 responded more strongly than Xifeng 20. Compared to aboveground biomass under no irrigation treatment, the aboveground biomass of Shijiazhuang 8 and Xifeng 20 improved by 87.0% and 57.8%, respectively, in a dry year, by 27.2% and 18.3%, respectively, in a normal year, and by 13.7% and 11.7%, respectively, in a humid year when irrigation were applied twice. The total water use (TWU) of the two cultivars also increased upon irrigation. The increase was more pronounced in the dry year than in the normal or humid years. However, there were no significant differences in the TWUs of the two cultivars. The water-use efficiency at grain-yield level (WUE_y) of Shijiazhuang 8 increased significantly upon irrigation in the dry year, did not change in the normal year, and showed a clear decline in the humid year, while the WUE_y of Xifeng 20 was reduced by irrigation in each of the three growing seasons. The harvest index (HI) was not altered by irrigation but it did vary by growing season. The HI of Shijiazhuang 8 was always higher than that of Xifeng 20. A positive correlation was found between both the WUE_y and the water-use efficiency at the aboveground-biomass level (WUE_bm) and the HI. This suggests that the changes in WUE_y as a result of irrigation are mainly due to changes in the WUE_bm and that the differences in WUE_y between the two cultivars were due to differences in WUE_bm and HI. These results suggest the following. (1) The TWUs in the two cultivars were roughly equal, although their levels of drought tolerance differed. (2) A wheat cultivar with moderate drought tolerance is expected to be more suitable for the semi-arid region of the NCP. The variety with strongly drought tolerance was able to keep its biomass high and to maintain grain yield under serious drought stress. (3) In order to both increase grain yield and WUE_y, two irrigations in a dry year, one irrigation in a normal year, and no irrigation in a humid year will give optimal results in the studied region.     

Effects of different water supply regimes on water use and yield performance of spring wheat in a simulated semi-arid environment

This research explores the limited irrigation strategies based on root-to-shoot communication that exists in spring wheat, and examines the effects of root-sourced signals on water use and yield performance of three genotypes of spring wheat (Triticum aestivum) under three different irrigation regimes. Four treatments, CT (well-watered management), DIu (supplying water to the upper layer to maintain soil moisture in the entire pot at 50–60% of field water capacity (FWC)), and DId (supplying water to the lower layer to maintain soil moisture in the entire pot at 50–60% FWC), were employed. The treatment DIu was used to simulate frequent post-sowing irrigation with small amount of water in each time, and DId was used to simulate pre-sowing irrigation with the same amount of water. Plants were grown in cylinder pots outdoors. A non-hydraulic root signal was induced from seedling to tillering stage in the treatment DId. But after the jointing stage, the signal resulted in a reduction in root biomass and root length in the upper layer and an increase in root biomass and root length in the middle layer as compared with the treatment DIu. The water use efficiencies of the three genotypes were the highest in the treatment DId and the lowest in the treatment DIu for the genotypes A and C. This suggests that under the conditions of the same amount of water supply frequent post-sowing irrigation to the upper soil layer had lower water use efficiency and grain yield, whereas pre-sowing irrigation to the lower soil layer tended to have higher grain yield and higher water use efficiency.     

灌溉水矿化度对土壤盐分及冬小麦产量的影响

为合理高效利用河北低平原区浅层地下咸水资源,采用田间试验的方法,系统研究了不同矿化度(1,2,4,6,8 g/L)灌溉水对土壤盐分分布与冬小麦产量的影响.结果表明,随灌溉水中矿化度的增加,0～20 cm厚度的土层土壤容重增加,同时土壤孔隙率逐渐降低.与淡水处理(1 g/L)相比,矿化度为2 g/L的灌溉水浇灌的麦田0～100 cm土层土壤平均盐分含量未出现明显增加;冬小麦拔节期、孕穗期和抽穗期的叶面积指数、株高以及单位面积穗数、穗粒数、千粒质量和籽粒产量未呈现明显差异.然而,当灌溉水矿化度增加到4 g/L以上时,0～100 cm土层土壤平均盐分含量大幅增加,植株生长受到明显抑制,籽粒产量出现显著下降,减产主要因素为咸水灌溉导致的冬小麦穗数减少.在该灌溉模式下,推荐冬小麦咸水灌溉的适宜矿化度低于2 g/L.     

Effect of different drip irrigation regimes on sugar beet (Beta vulgaris L.) yield, quality and water use efficiency in Middle Anatolian, Turkey

Agricultural production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant plant varieties or water management for arid and semi-arid areas under water shortage conditions. A field study was conducted to determine effects of seasonal deficit irrigation on plant root yield, quality and water use efficiency (WUE) of sugar beet for a 2-year period in the semi-arid region. Irrigations were applied when approximately 50–55% of the usable soil moisture was consumed in the effective rooting depth at the full irrigation (FI) treatment. In deficit irrigation treatments, irrigations were applied at the rates of 75, 50 and 25% of full irrigation treatment on the same day. Irrigation water was applied by a drip irrigation system. Increasing water deficits resulted in a relatively lower root and white sugar yields. The linear relationship between evapotranspiration and root yield was obtained. Similarly, WUE was the highest in DI25 irrigation conditions and the lowest in full irrigation conditions. According to the averaged values of 2 years, yield response factor (k _y ) was 0.93 for sugar beet. Sugar beet root quality parameters were influenced by drip irrigation levels in both years. The results revealed that irrigation of sugar beet with drip irrigation method at 75% level (DI25) had significant benefits in terms of saved irrigation water and large WUE, indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25% saving of irrigation water (DI25) caused 6.1% reduction in the net income.     

微咸水灌溉下土壤水盐动态及对作物产量的影响

华北平原农业灌溉用水非常紧缺,水资源日益缺乏与粮食需求日益增多之间的矛盾尖锐。充分利用微咸水资源是缓解这一矛盾的重要途径之一。该文以中国农业大学曲周试验站1997－2005年冬小麦和夏玉米微咸水灌溉田间长期定位试验为基础,研究了充分淡水、充分淡咸水、关键期淡水、关键期淡咸水和不灌溉等5个处理下土壤饱和电导率和含盐量的动态变化,探讨了微咸水灌溉对冬小麦和夏玉米产量的影响。结果表明：土壤水盐动态呈受灌溉和降雨影响的短期波动和受季节更替影响的长期波动;在正常降雨年份,使用微咸水进行灌溉是可行的,不会导致土壤的次生盐渍化;微咸水灌溉虽然导致冬小麦和夏玉米产量降低10%～15%,但节约淡水资源60%～75%。如果降雨量达到多年平均水平以及微咸水灌溉制度制订合理,微咸水用于冬小麦/玉米田间灌溉前景广阔。     

不同覆盖方式对土壤水热及猕猴桃产量的影响

针对南方季节性干旱和夏季土壤高温胁迫所造成的猕猴桃产量与品质下降等问题,探索合理有效的覆盖措施来改善果园的土壤水热环境,从而实现南方猕猴桃产业的可持续发展.通过大田观测试验,研究黑膜(H)、白膜(B)、防草布(F)、防草布+白膜(F+B)、秸秆(J)、不覆盖(CK)6种不同覆盖处理下土壤水分、温度的变化规律,并比较相应处理的猕猴桃产量与品质差异.相比处理CK,覆盖处理保水效果较好,处理H,B,F,F+B,J在0～50 cm土壤含水率分别提高了1.1%,1.3%,2.2%,2.9%,1.6%,随土层深度的增加,土壤含水率明显提升.相比处理CK,夏季单一覆盖处理使0～25 cm土壤温度降低了0.8～2.5℃,而F+B组合覆盖处理土壤温度升高了0.9℃,同时覆盖处理缩小了温度日变化0.9～2.1℃,处理F尤为显著.各覆盖处理使猕猴桃单果质量提高了0.1%～7.7%,同时可提高糖酸比3.8%～33.6%.防草布覆盖既可改善猕猴桃土壤的水热环境,又能提高猕猴桃的产量与品质,是该区果园管理较适宜的覆盖方式.     

不同水分处理下液膜覆盖对夏玉米生长及产量的影响

针对塑料地膜对农业生产造成的严重污染问题,运用对照处理方法,探讨了液体地膜覆盖对夏玉米生长发育及产量等方面的影响。结果表明,液膜覆盖使夏玉米株高和茎粗均比对照偏大,其中,低水分处理下差异最为显著。夏玉米叶面积指数低水分处理时液膜覆盖在生育前期较对照偏大,生育后期偏小;而中、高水分下液膜覆盖叶面积指数在整个生育期内均比对照偏大。液膜覆盖使夏玉米光合速率和蒸腾速率显著增大,有利于光合产物的形成。低水分处理下液膜覆盖增产效果最好,增产率达到56.97%,产投比为1.695,高水分下液膜覆盖增产效果最差,增产率仅为15.57%,液膜覆盖产投比小于对照。研究认为,夏玉米液膜覆盖能有效抵抗干旱逆境从而达到节水增产的显著效果。     

水、氮和保水剂对小粒咖啡水氮利用的影响

为探求小粒咖啡幼树的最佳水氮管理及高效利用模式,通过2种灌水水平（中水（WM,65%～80%FC）和低水（WL,50%～65%FC））、3种施氮水平（高氮（NH,0.40g/kg）,低氮（NL,0.20g/kg）和无氮（Nz,0））和2种保水剂水平（有保（SH,1kg/m^3）和无保（SZ,0））的完全处理组合,研究灌水、氮素营养及保水剂对小粒咖啡幼树根区土壤水氮累积、干物质生产和水氮吸收利用的影响.研究表明：和WL相比,WM提高总干物质量、水分利用率、氮素吸收总量和氮素干物质生产效率分别为86.0%,36.4%,73.1%和5.3%.和NZ相比,NL和NH提高水分利用率和氮素吸收总量的效果基本相同.和SZ相比,SH提高土壤硝态氮质量比、总干物质量、水分利用率和氮素吸收总量分别为21.9%～43.0%,78.3%,68.9%和91.2%,而降低氮素干物质生产效率10.0%.在中等供水（65%～80%FC）和低氮（NL,0.20g/kg）条件下,配施保水剂能有效调控土壤水氮供给状况,促进干物质生产和提高水氮利用效率.因此,在本试验条件下,有利于小粒咖啡水氮高效利用的最优试验组合为WM NL SH.     

保水剂对冬小麦不同生育阶段土壤水分及利用的影响

为探明保水剂施用后对冬小麦不同生育阶段水分利用的作用机理,在豫西丘陵旱作区,通过大田试验,研究了保水剂对冬小麦不同生育阶段的保水、作物的耗水特征、水分利用效率等的影响。结果表明：保水剂提高了冬小麦不同生育阶段0～100 cm土层的土壤含水量、促进了生物量的积累、降低了小麦耗水量、提高了小麦产量和水分利用效率。各处理中,60和90 kg/hm2处理的土壤含水量及储水量均较其他处理高,而耗水量最低。播种-拔节期,保水剂用量越高干物质积累越显著;拔节-孕穗期及灌浆-收获期,60 kg/hm2处理较对照增加的干物质量最高;而孕穗-灌浆期,30 kg/hm2干物质量增加最为显著。各生育阶段,除孕穗-灌浆期外,60 kg/hm2处理的水分利用效率均较高。最终,60 kg/hm2处理的产量和水分利用效率均最高,较对照增产47.4%,水分利用效率增加10.6 kg/(mm·hm2)。     

Application of time-domain reflectometry (TDR) soil moisture miniprobe for the determination of unsaturated soil water characteristics from undisturbed soil cores

Summary Construction and operating characteristics of a TDR soil moisture miniprobe, that can be inserted through the wall of a metal cylinder, are shown. A laboratory stand for monitoring unsaturated water flow in undisturbed soil cores, involving a set of TDR miniprobes in combination with a set of minitensiometers, is described. This stand was used for frequent readings of instantaneous profiles of moisture and matric potential during transition from saturated to air dry state, in order to compute the unsaturated soil water characteristics. Some methodical aspects of the applied data processing algorithm are outlined.     

Different drip irrigation regimes affect cotton yield, water use efficiency and fiber quality in western Turkey

Decreasing in water availability for cotton production has forced researchers to focus on increasing water use efficiency by improving either new drought-tolerant cotton varieties or water management. A field trial was conducted to observe the effects of different drip irrigation regimes on water use efficiencies (WUE) and fiber quality parameters produced from N-84 cotton variety in the Aegean region of Turkey during 2004 and 2005. Treatments were designated as full irrigation (T₁₀₀, which received 100% of the soil water depletion) and those that received 75, 50 and 25% of the amount received by treatment T₁₀₀ on the same day (treatments T₇₅; T₅₀ and T₂₅, respectively). The average seasonal water use values ranged from 265 to 753 mm and the average seed cotton yield varied from 2550 to 5760 kg ha⁻¹. Largest average cotton yield was obtained from the full irrigation treatment (T₁₀₀). WUE ranged from 0.77 kg m⁻³ in the T₁₀₀ to 0.98 kg m⁻³ in the T₂₅ in 2004 growing season and ranged from 0.76 kg m⁻³ in the T₁₀₀ to 0.94 kg m⁻³ in the T₂₅ in 2005 growing season. The largest irrigation water use efficiency (IWUE) was observed in the T₂₅ (1.46 kg m⁻³), and the smallest IWUE was in the T₁₀₀ treatment (0.81 kg m⁻³) in the experimental years. A yield response factor (k_y) value of 0.78 was determined based on averages of two years. Leaf area index (LAI) and dry matter yields (DM) increased with increasing water use for treatments. Fiber qualities were influenced by drip irrigation levels in both years. The results revealed that well-irrigated treatments (T₁₀₀) could be used for the semi-arid climatic conditions under no water shortage. Moreover, the results also demonstrated that irrigation of cotton with drip irrigation method at 75% level (T₇₅) had significant benefits in terms of saved irrigation water and large WUE indicating a definitive advantage of deficit irrigation under limited water supply conditions. In an economic viewpoint, 25.0% saving in irrigation water (T₇₅) resulted in 34.0% reduction in the net income. However, the net income of the T₁₀₀ treatment is found to be reasonable in areas with no water shortage.     

Effect of initial soil salinity and subirrigation water salinity on potato tuber yield and size

A field lysimeter study was conducted to investigate the effect of initial soil salinity and salinity level of brackish subirrigation water on tuber weight and tuber size of three potato (Solanum tuberosum L.) cultivars (Kennebec, Norland and Russet Burbank) under simulated arid conditions. Both saline and non-saline initial soil conditions were simulated in a total of 36 lysimeters. Eighteen lysimeters were flushed with fresh water (0.2 dS/m), while the remaining 18 lysimeters were flushed with brackish water (2 dS/m). For each soil condition, two subirrigation water concentrations, 1 and 9 dS/m, were used in nine lysimeters each. For each subirrigation water treatment, three potato cultivars were grown. In all lysimeters, water table was maintained at 0.4 m from the soil surface. Arid conditions were simulated by covering the lysimeter top with plastic mulch, allowing the potato shoots to grow through a cut in the mulch. The average root zone salinities (EC_w) were found to be 1.2 and 1.5 dS/m in non-saline lysimeters subirrigated with 1 and 9 dS/m waters, respectively. The corresponding salinities were 3.2 and 3.7 dS/m in the saline lysimeters. Across cultivars, there was no significant effect of either initial soil salinity or subirrigation water salinity on total tuber weight. However, the weight of Grade A tubers was higher in non-saline soil than in saline soil. Kennebec and Russet Burbank Grade A tuber weights were not affected by the initial soil salinity. On the contrary, a significant reduction in Grade A and total tuber weight under initially saline soil was evident for the Norland cultivar.     

Effect of irrigation and nitrogen on yield,yield components and water use efficiency of barley in Saudi Arabia

Water use efficiency and yield of barley were determined in a field experiment using different irrigation waters with and without nitrogen fertilizer on a sandy to loamy sand soil during 1994–1995 and 1995–1996. Depending upon different fertilizer treatments, the overall mean crop yield ranges for two crop seasons were: greenmatter from 19.48–55.0 Mg ha⁻¹ (well water) and 21.92–66.5 Mg ha⁻¹ (aquaculture effluent); drymatter from 6.86–20.69 Mg ha⁻¹ (well water) and 7.87–20.90 Mg ha⁻¹ (aquaculture effluent); biomass from 4.12–21.31 Mg ha⁻¹ (well water) and 8.10–19.94 Mg ha⁻¹ (aquaculture effluent) and grain yield from 2.12–5.50 Mg ha⁻¹ (well water) and 3.25–7.25 Mg ha⁻¹ (aquaculture effluent). The WUE for grain yield was 3.37–8.74 kg ha⁻¹ mm⁻¹ (well water) and 5.17–11.53 kg ha⁻¹ mm⁻¹ (aquaculture effluent). The WUE for total biomass ranged between 6.55–33.88 kg⁻¹ ha⁻¹ mm⁻¹ (well water) and 12.88–31.70 kg ha⁻¹ mm⁻¹ (aquaculture effluent). The WUE for drymatter was 10.91–32.90 kg ha⁻¹ mm⁻¹ (well water) and 12.51–33.22 kg ha⁻¹ mm⁻¹ (aquaculture effluent). It was found that grain yield and WUE obtained in T-4 and T-5 irrigated with well water and receiving 75 and 100% nitrogen requirements were comparable with T-4 and T-5 irrigated with aquaculture effluent and receiving 0 and 25% nitrogen requirements. In conclusion, application of 100 to 150 kg N ha⁻¹ for well water and up to 50 kg N ha⁻¹ for aquaculture effluent irrigation containing 40 Mg N l⁻¹ would be sufficient to obtain optimum grain yield and higher WUE of barley in Saudi Arabia.     

Effect of residual sodium carbonate in irrigation water on the soil sodication and yield of palmarosa (Cymbopogon martinni) and lemongrass (Cymbopogon flexuosus)

The effects of residual sodium carbonate (RSC) in irrigation water on soil sodication and yield and cation composition of palmarosa (Cymbopogon martinii Roxb. Wats) and lemongrass (Cymbopogon flexuosus Steud Wats) were studied in the open bottom reinforced concrete cemented (RCC) cylindrical barrels embedded in the field and filled with sandy loam soils. The results indicated that the increasing RSC in irrigation water significantly increased the pH, electrolyte conductivity (ECe) and SARe of the soil and, hence, considerably decreased the herb and oil yield of both the palmarosa and lemongrass. The reduction in total herb yield was 14.5, 18.3, 28.8 and 32.0% in palmarosa and 38.6, 46.0, 57.7 and 62.6% in the lemongrass over control at 4.0, 8.0, 12.0 and 16.0 meq/l of RSC, respectively. The total oil yield of palmarosa increased by 22.6% with the increase in RSC from 2.0 (control) to 4.0 meq/l and further increase in RSC decreased the oil yield by 13.0, 22.4 and 22.9% over control at 8,12 and 16 meq/l of RSC, respectively. The total oil yield of lemongrass was decreased by 27.0, 39.4, 47.7 and 50.8% over control at 4, 8, 12 and 16 meq/l, respectively. The concentration of Na increased significantly and K and Ca decreased with increase in RSC of irrigation water in vegetative tissues of both species. The lemongrass accumulates significantly greater amount of Na in shoot tissues as compared to palmarosa and it failed to survive at high RSC after 21 months of transplanting. The results suggests that palmarosa is more tolerant to irrigation water sodicity than the lemongrass.     

Effects of elevated CO2 concentration on growth and water use efficiency of winter wheat under two soil water regimes

Winter wheat (Triticum aestivum L. cv. Kenong9204) was grown in open top chambers with either ambient or elevated CO₂ concentrations (358 ± 19 μmol mol⁻¹ or 712 ± 22 μmol mol⁻¹, respectively) in well-watered or drought conditions. Although elevated CO₂ did not significantly affect the height of the plants at harvest, it significantly increased the aboveground biomass by 10.1% and the root/shoot ratio by 16.0%. Elevated CO₂ also significantly increased the grain yield (GY) by 6.7% when well-watered and by 10.4% when drought stressed. Specifically, in the well-watered condition, this increase was due to a greater number of ears (8.7% more) and kernels (8.6). In the drought condition, it was only due to a greater number of spikes (17.1% more). In addition, elevated CO₂ also significantly increased the water use efficiency (WUE) of the plants by 9.9% when well-watered and by 13.8% under drought conditions, even though the evapotranspiration (ET) of the plants did not change significantly. Elevated CO₂ also significantly increased the root length in the top half of the soil profile by 35.4% when well-watered and by 44.7% under drought conditions. Finally, elevated CO₂ significantly increased the root water uptake by 52.9% when well-watered and by 10.1% under drought conditions. These results suggest that (1) future increases in atmospheric CO₂ concentration may have a significant effect on wheat production in arid and semiarid areas where wheat cultivation requires upland cropping or deficit irrigation; (2) wheat cultivars can be developed to have more tillers and kernels through selective breeding and field management; and (3) fertilizer and water management in topsoil will become increasingly important as atmospheric CO₂ concentration rises.     

Water use of young ‘Fuji’ apple trees at three soil moisture regimes in drainage lysimeters

Studies were conducted during 4 months of each growing season in 1994 and 1995 to measure water use of young apple trees (Malus domestica Borkh. cv ‘Fuji’) growing under different soil moisture regimes in temperate climate conditions and to evaluate monthly crop coefficients of such conditions. To do so, double pot lysimeters under a transparent rain shield were designed and installed. The three soil moisture regimes in three replicates each were: (A) drip-irrigation at −50 kPa of soil matric potential (IR50); (B) drip-irrigation at −80 kPa of soil matric potential (IR80); and (C) constant shallow water table at 0.45 m below the soil surface (WT45). In each treatment, soil surface was maintained with or without turf grasses. Monthly water use was not different in drip-irrigated treatments (IR50 and IR80), but greatest in the WT45 treatment. Monthly crop coefficients increased linearly in time for drip-irrigated apple trees (r² values of 0.76^*** for IR50 and of 0.77^*** for IR80), while those obtained in the WT45 treatment fluctuated. Leaf water potential (LWP) of drip-irrigated trees was similar until 63 days after treatment (DAT), but the values for IR80 trees began to decline thereafter. The LWP of WT45 trees decreased from 48 DAT. Temporal variations in leaf water content (LWC) was similar to that of LWP, except for two abrupt decreases in IR80 trees. The LWC of WT45 trees began to decrease from 59 DAT, and this occurred 2 weeks after the reduction in LWP. Average shoot length of IR50 trees was greater than that of IR80 and WT45 trees. The results of this study provided water use and crop coefficients for apple trees in relation to soil moisture regimes under temperate climate.