Water Use Efficiency For Grain Research Articles

Plant Growth Regulators Improve Grain Production and Water Use Efficiency of Foeniculum vulgare Mill. under Water Stress.

The development of methods increasing plant water use efficiency (WUE) would enhance the ability to grow wild aromatic and medicinally important species. The aim of this research was to determine the effect of plant growth regulators (PGRs) applied by spraying on stress resistance and WUE of fennel subjected to water stress. Plants in the generative stage were more drought tolerant than those in the vegetative stage. Water stress at vegetative stage decreased plant biomass and grain yield by 60% and 61%, respectively. Severe water stress in vegetative stage reduced grain production by 56%, and grains had 43% lower mass than those from non-stressed plants. Application of PGRs at both stages of growth increased grain yield and biomass, but the magnitude of increase depended on the type and application time of PGRs. Plants grown in well-watered conditions and sprayed with methyl jasmonate during the vegetative stage had the highest grain production (2.7 g plant−1), whereas under moderate water stress, plants yielded the best (2.1 g plant−1) when sprayed with epibrassinolide. The maximum WUE for grain (0.91 g L−1) and essential oil production (20 mg L−1) was noted in plants exposed to moderate stress and treated with methyl jasmonate during the vegetative stage.

Improvement of wheat productivity and soil quality by arbuscular mycorrhizal fungi is density- and moisture-dependent

Adaptive management of arbuscular mycorrhizal fungi (AMF) provides a new option for sustainable agriculture. Previous studies showed that the functional role of AMF was frequently dependent on soil moisture and planting densities in the semiarid environment. However, a systematic quantitative analysis of the effects of AMF inoculation on crop productivity and soil quality needs to be investigated. Therefore, a 2-year field experiment was conducted to test the inoculation effects of AMF (Funneliformis mosseae) on wheat (Triticum aestivum L.) productivity and soil quality in the semiarid Loess Plateau under two water regimes (irrigated and non-irrigated) with seven plant densities in year 2017 and 2018. Our results showed that in the non-irrigated treatment, inoculation with AMF greatly increased dryland wheat aboveground biomass, crop productivity, water use efficiency, rhizosphere soil organic carbon, soil organic carbon to total nitrogen ratio, microbial biomass carbon to nitrogen ratio, and microbial biomass carbon and nitrogen (P < 0.05) compared to the non-inoculated treatment. For example, compared with non-inoculated plants, the grain yield in the non-irrigated but inoculated plants increased by 59 ± 28% in 2017 and 36 ± 2.8% in 2018, and the water use efficiency for grain increased by 53 ± 26% and 25 ± 12% in 2017 and 2018, respectively. However, the different results were observed under irrigated conditions. In the irrigated treatment, AMF inoculation had a slightly positive effect on grain yield and soil quality at low plant density but was negative at higher plant densities. Here we demonstrated for the first time that AMF inoculation significantly improved wheat productivity and soil quality, while its effects were conditionally density- and moisture-dependent. Therefore, optimizing AMF addition is an effective measure for sustainable agricultural development and provides a novel solution for the management of soil degradation management in the semiarid area of the Loess Plateau.

Water-conserving and biomass-allocation traits are associated with higher yields in modern cultivars compared to landraces of soybean [Glycine max (L.) Merr.] in rainfed water-limited environments

Drought is one of the main factors restricting the productivity of soybean (Glycine max L.), especially in arid and semi-arid areas where the crop may suffer from frequent and severe drought events unless irrigated. The aim of the present study was to determine the plant responses to water deficits in four landraces and four modern soybean cultivars that differed in yield in rainfed water-limited environments to determine the characteristics associated with yield under drought in the field and under a rainout shelter. During a slow progressive soil drying cycle, the stomata began to close at higher soil water contents (SWC) of 65–67% vs 61–63%, photosynthesis began to decrease at higher SWC of 60–62% vs 52–54% and leaf hydraulic conductance fell by 20% at higher SWC of 50–67% vs 36–48%, while the leaf relative water content began to decrease at lower SWC of 30–35% vs 38–39% in modern cultivars than landraces, respectively, indicating that the modern cultivars exhibited greater isohydric behaviour than the landraces. Water use after flowering was lower in the modern cultivars, consistent with the conservative leaf physiology, but yield was not correlated or negatively correlated with water use so the higher yield and water use efficiency for grain in the modern cultivars was associated with lower water use and higher distribution of biomass to grain, i.e., a higher harvest index. We conclude that breeders of modern high-yielding cultivars of soybean for rainfed semiarid environments have selected for lower biomass and leaf area, larger grain size and higher harvest index, while also selecting for stronger isohydric behaviour and water-conserving traits.

Drought-induced change in yield capacity of ten wheat cultivars in relation to their vegetative characteristics at heading stage.

Ten wheat (Triticum aestivum L.) cultivars were tested in a semi-field experiment for drought response in terms of their flag leaf vigor, whole shoot growth and ultimate yield capacity. At booting stage, 25% of field capacity was held for 3weeks, then the plants were normally irrigated. Based on split plot analysis of the pooled data, the order in which the source of variation could affect the estimated traits was watering level, then cultivar and finally the combination of both. At p ≤ 0.05, significant positive linear correlation was recorded between the drought-induced change in grain total carbohydrate content and leaf total carbohydrate content, between biological yield and each of water use efficiency for biomass and evapotranspiration efficiency as well as between economic yield and each of leaf catalase activity, water use efficiency for grain and hundred kernel mass. On contrary, significant negative correlation was recorded between the drought-induced change in shoot evapotranspiration rate and each of leaf proline content and shoot water content. Based on the drought-induced change in the estimated vegetative and yield traits, cluster analysis could sequester the concerned cultivars into drought-tolerant, moderate and sensitive ones; with Sids 13 being the most drought-tolerant cultivar as well as Shandaweel 1 and Giza 168 as the most drought-sensitive ones.

Assessing Wheat Yield, Biomass, and Water Productivity Responses to Growth Stage Based Irrigation Water Allocation

Increasing irrigated wheat yields is important to the overall profitability of limited-irrigation cropping systems in western Kansas. A simulation study was conducted to (1) validate APSIM‘s (Agricultural Production Systems sIMulator) ability to simulate wheat growth and yield in Kansas, and (2) apply the model to assess the response of wheat yield, biomass, and water productivity to irrigation allocation based on growth stage. The methodology involved combining short-term experimental data, long-term historical weather data (1950-2013), and mechanistic crop growth simulation to determine optimum irrigation management strategies. The model adequately simulated measured soil water in the profile. The goodness-of-fit test between the observed and simulated values for phenology, yield, biomass, and ET of the experimental cultivar in 2008-2009 in our study site agreed well with the ‘Batten winter‘ wheat cultivar in APSIM. Results indicated that, on average, an irrigation allocation of 100 mm increased wheat yield by 14% to 46% compared to rainfed (dryland) production. Application of an additional 100 mm of irrigation did not improve wheat yield substantially (on average -1 ). Higher water productivity for grain yield was obtained when irrigation was applied at booting and heading. Overall, irrigation water use efficiency for grain decreased with an increase in irrigation allocation. The highest irrigation water use efficiency was simulated for wheat grown with a limited irrigation allocation of 100 mm applied at booting and heading. This study demonstrates that limited irrigation targeted at sensitive growth stages could enhance wheat yields and improve water productivity of water-limited cropping systems.

Recently-released genotypes of naked oat (Avena nuda L.) out-yield early releases under water-limited conditions by greater reproductive allocation and desiccation tolerance

Naked oat (Avena nuda L.) is becoming increasingly popular because of its high nutritive value and increased yields. As naked oat is grown in marginal environments, one of the limitations to yield is drought stress. In this study conducted in the field and a rainout shelter, the yield, water relations, and physiological and biochemical responses to drought of six genotypes, three released since 2008 (recently-released, RR) and three genotypes released at least 60 years earlier (early-released, ER) were compared. The grain yield, harvest index (HI) and water use efficiency for grain were higher in the RR than ER genotypes under rainfed and irrigated conditions in the field and under drought and well-watered conditions in the rainout shelter. Aboveground biomass and HI had significant direct effects on grain yield, while leaf dry weight was negatively associated with grain yield in the rainout shelter. During a progressive soil drying experiment, the threshold soil water content (SWC) when stomatal conductance and photosynthesis began to decrease was lower in the RR [48–52% field capacity (FC)] than ER (54–58% FC) genotypes, but whole plant transpiration began to decrease when the leaf water potential and relative water content began to decrease at a threshold SWC of 31–44% FC in both the RR and ER genotypes. The beginning of the decrease in stomatal conductance and photosynthesis was associated with the increase in leaf abscisic acid concentration, but higher osmolyte accumulation, greater osmotic adjustment and less lipid peroxidation in the RR genotypes than the ER genotypes occurred at low SWC (below 30% FC) and are associated with greater desiccation tolerance in the RR genotypes. We conclude that the higher yields in the RR genotypes of naked oat are associated with selection for higher reproductive allocation and desiccation tolerance. The role of stomatal closure and osmotic adjustment on adaptation to drought are discussed.

Effects of drought stress on morphological, physiological and biochemical characteristics of wheat species differing in ploidy level.

Modern hexaploid wheat has several diploid and tetraploid predecessors. Morpho-physiological adaptation and the adaptation to drought of these different ploidy wheat species is largely unknown. To investigate the adaptation to drought stress, eight accesssions (two wild diploid (2n) accessions of Aegilops tauschii Coss., two domesticated diploid (2n) accessions of Triticum monococcum L., two domesticated tetraploid (4n) accessions of Triticum dicoccum Schrank ex Schübl. and two domesticated hexaploid (6n) accessions of Triticum aestivum L.) were exposed to three water regimes: (i) well-watered control (WW, 80% field capacity (FC)), (ii) moderate water stress (MS, 50% FC), and (iii) severe water stress (SS, 25% FC) from 30 days after sowing to maturity. The results showed that accession (A), water regime (W), and the interaction of A×W significantly affected yield, morpho-physiological traits, biochemical characteristics and biomass allocation. In the WW treatment, the aboveground biomass, ear biomass, grain yield and harvest index increased, whereas the number of spikes and spikelets per plant decreased from accessions of T. monococcum to T. dicoccum to T. aestivum. Across all accessions, yields decreased by 29% under moderate water stress and 61% under severe water stress. In all three water regimes, yields were positively correlated with photosynthesis (Pn) per plant (Pn×leaf area) at jointing and anthesis, largely the result of the differences and changes in leaf area. Water use efficiency for grain (WUEG) decreased by 2-6% in T. monococcum, but it increased by 15-16% in T. dicoccum and T. aestivum under drought stress. Analysis of the allometric relationships between aboveground biomass (MAB) and root biomass (Mroot) in the different species indicated that less biomass was allocated to roots with greater polyploidy while more biomass was allocated to roots with drought in A. tauschii, but not in the domesticated species. We conclude that domestication, selection and breeding of higher ploidy wheat has increased wheat yields primarily by increasing aboveground biomass and harvest index, increases that were maintained under water stress.

Exploring micro-field water-harvesting farming system in dryland wheat (Triticum aestivum L.): An innovative management for semiarid Kenya

Micro-field rain-harvesting farming system (MRFS) has demonstrated great potentials to enhance field productivity and profitability of dryland wheat (Triticum aestivum L.) in semiarid eastern Asia, yet little is known whether this system results in desired effects in semiarid Africa such as Kenya. A two-year field experiment was conducted during 2012 and 2013 growing seasons to evaluate the effects of introduced MRFS on water availability, field productivity and economic benefits using a local wheat (T. aestivum L.) cultivar DUMA in a semiarid site of Kenya. Five treatments were designed as: 1) ridge and furrow with transparent plastic mulching (RFT); 2) ridge and furrow with black plastic mulching (RFB); 3) ridge and furrow with grass straw mulching (RFS); 4) ridge and furrow without mulching (RF); and 5) traditional flat planting (CK). The results showed that mulching treatments (RFT, RFB and RFS) significantly decreased the evapotranspiration (ET) by 11.4–88.5mm, increased wheat grain yield by 60%–163%, above-ground biomass by 58%–104% and water use efficiency for grain by 68%–271%, compared with CK over two growing seasons. RFT and RFB treatments resulted in maximal soil water storage at 1-m depth and the greatest harvest index among all treatments. Linkage analyses indicated that grain yield showed significantly positive correlation with plant height, leaf area and major spike components (P≤0.05), suggesting that plant type of wheat was altered for better yield production as a result of MRFS operation. More importantly, economic ratios of output to input were also calculated and compared. The average ratio of output to input for CK was 3.86, slightly lower than 4.28, 4.06, 5.86 and 5.34 for RFT, RFB, RFS and RF, respectively across two growing seasons. In particular, net incomes in MRFS (RFT, RFB, RFS and RF) were increased by 145%, 128%, 117% and 82% respectively, compared with that of CK. In conclusion, on-field rain-harvesting farming system provides an innovative management to boost the productivity and profitability of dryland wheat, and a potential solution to cope with food security in semiarid Kenya.

A comparative appraisal of urea super granule application in raised bed and prilled urea application in conventional planting for transplanted boro rice (Oryza sativa)

Utilization of urea super granule (USG) with raised bed cultivation system for transplanted boro (winter, irrigated) rice production is a major concern now days. A field experiment was conducted in the chuadanga district of Bangladesh to compare the two cultivation methods: deep placement of USG on raised bed with boro rice, and prilled urea (PU) broadcasting in conventional planting. Results showed that USG in raised bed planting increased grain yields of transplanted boro rice by up to 18.18% over PU in conventional planting. Deep placement of USG in raised bed planting increased the number of panicle m-2, number of grains panicle-1 and 1000-grains weight of boro rice than the PU in conventional planting. Better plant growth was observed by deep placement of USG in raised bed planting compared to PU in conventional planting. Sterility percentage and weed infestation were lower on USG in raised bed planting compared to the PU in conventional planting methods. Forty seven percent irrigation water and application time could be saved by USG in raised bed planting than PU in conventional planting. Deep placement of USG in bed saved N fertilizer consumption over conventional planting. Water use efficiency for grain and biomass production was higher with deep placement of USG in bed planting than the PU broadcasting in conventional planting methods. Similarly, agronomic efficiency of N fertilizer by USG in bed planting was significantly higher than the PU broadcasting in conventional planting. This study concluded that deep placement of USG in raised bed planting for transplanted boro rice is a new approach to achieve fertilizer and water use efficiency as well as higher yield and less water input compared to existing agronomic practices in Bangladesh.

Utilization of Urea Super Granule in Raised Bed Versus Prilled Urea in Conventional Flat Method for Transplanted Aman Rice (Oryza Sativa)

Bed planting with urea super granule (USG) application of rice production systems is very new and research on it is still at an introductory phase. Impact of granular urea application on growth and yield of transplanted aman rice as well as evaluation of water and fertilizer use efficiency of rice-fallow-rice cropping system was investigated under raised bed cultivation method. Result showed that the USG in bed planting method increased grain yield of transplanted aman rice up to 12.32% over prilled urea (PU) broadcasting in conventional method. The USG application in bed planting method increased the number of panicle m-2, number of grains panicle-1 and 1000-grains weight of rice than the PU in conventional method. Sterility percentage and weed infestation were lower at USG application in bed planting method than the PU in conventional method. Forty percent irrigation water and time for application could be saved through the USG in bed planting than the PU broadcasting in conventional method. Water use efficiency for grain and biomass production was higher by the USG application in bed planting than the PU broadcasting in conventional method. Likewise, agronomic efficiency of the USG in bed planting was higher than the PU broadcasting in conventional method. This study concluded that the USG in bed planting method is a new approach to get better fertilizer and water use efficiency as well as higher yield compared to the existing agronomic practice in the world.

Water use and productivity of a sorghum–cowpea–bottle gourd intercrop system

Water is the main factor affecting crop production in sub-Saharan Africa. It was hypothesized that intercropping sorghum (S) with either cowpea (C) or bottle gourd (B) would result in better productivity and water use efficiency (WUE). This was evaluated using a split-plot design with sub-plots arranged in a randomised complete block manner within the main plot, replicated thrice. Water regimes [full irrigation (FI), deficit irrigation (DI) and rainfed (RF)] were allocated to the main plots. Sub-plots comprised intercrop combinations, SS (sole), C (sole), B (sole), SC (intercrop) and SB (intercrop). Data collected included soil water content (SWC), plant height (PH)/vine length, leaf number (LN), tillering (T)/branching, leaf area index (LAI), relative leaf water content (RWC), stomatal conductance (gs) and chlorophyll content index (CCI) as well as biomass accumulation and partitioning. Yield and yield components, water use (WU) and WUE for grain (WUEg) were calculated at harvest. Land equivalent ratio (LER) was used to evaluate productivity of the intercrop. Sorghum canopy size decreased (P<0.05) (−6.7%, −10.6%, −89% and −79% for PH, LN, T and LAI, respectively) with decreasing water availability. Sorghum growth and development were unaffected by intercropping. Intercropping sorghum with cowpea improved gs (23%) and CCI (6.56%) of sorghum under low water availability. Productivity of sorghum across varying water regimes and cropping systems was stable with final biomass, yield and harvest index of 2.4tha−1, 0.98tha−1 and 35%, respectively. Overall, LER showed a 46% increase in productivity across all intercrop systems. Intercropping marginally increased WU (5.64%). Improvements of WUEg were observed under SC and SB (54.65% and 46.98%, respectively) relative to SS. Intercropping sorghum with cowpea is recommended for semi-and arid environments since it promoted efficient use of water.

Increasing yield and agronomic efficiency of boro rice (Oryza sativa) by fertigation with bed planting compared with conventional planting.

The fertigation technique with raised bed planting for transplanted boro (winter, irrigated) rice production is a research focus nowadays. A field experiment compared two cultivation methods: the fertigation technique within raised bed planting on boro rice, and fertilizer broadcasting in the conventional planting method. Compared to conventional fertilizer broadcasting, results showed that the new fertigation technique in raised bed planting increased grain yield of transplanted boro rice by up to 17.04%. It yielded a greater number of panicles per square meter, a greater number of grains per panicle, higher 1000-grains weight, and better plant growth attributes. Sterility percentage and weed infestation were lower. Thirty six percent of irrigation water and time for application could be saved. Water use efficiency for grain and biomass production was higher. The agronomic efficiency of nitrogen (N) fertilizer was significantly higher. This study concluded that fertigation in raised bed planting for transplanted boro rice is a new approach with higher yield and higher fertilizer and water use efficiency than the existing agronomic practice in Bangladesh. Keywords: boro rice, fertigation with bed planting, de-nitrification, water use efficiency, harvest index, irrigated water management DOI: 10.3965/j.ijabe.20140705.004 Citation: Bhuyan M H M, Ferdousi M R, Iqbal M T. Increasing yield and agronomic efficiency of boro rice (Oryza sativa) by fertigation with bed planting compared with conventional planting. Int J Agric & Biol Eng, 2014; 7(5): 34－47.

Does a mixture of old and modern winter wheat cultivars increase yield and water use efficiency in water-limited environments?

Use of mixtures of cultivars is an alternative to a monocultural crop and is considered one option to reduce the risks for producers. The objective of this study was to evaluate the grain yield and water use efficiency of a range of proportions of two winter wheat cultivars – an old landrace (Pingliang 40, PL) and a modern cultivar (Changwu 135, CW). Field experiments were conducted in 2004–2005 and 2005–2006 at Changwu Agricultural Research Station on the Loess Plateau of China. Along with pure stands of each genotype, four mixed stands, 20% PL and 80% CW (PL2:CW8), 40% PL and 60% CW (PL4:CW6), 60% PL and 40% CW (PL6:CW4), 80% PL and 20% CW (PL8:CW2), were established in the first year and a single mixture of 50% PL and 50% CW (PL5:CW5) was established in the second year. The grain yield of the mixtures fell between the yields of the respective monocultures under mild drought condition in 2005, while the yield of PL5:CW5 was not significantly different from that of the modern cultivar, CW, but higher than that of the landrace PL under the more unfavorable conditions (moderate drought) of 2006 (P<0.05). At the same proportions in the mixture, greater grain yield in PL than that in CW was associated with the higher spike density, higher grain number and larger grains. In 2005, the water use efficiency for grain (WUEg) of CW was significantly higher than that of PL, while the WUEg of the mixtures, except PL8:CW2, was intermediate between the WUEg of the two monocultures. In 2006, the WUEg of PL5:CW5 was higher than both PL and CW (P<0.05). In the mixtures, plant height increased in PL, but was reduced in CW, while the flag leaf area increased in both cultivars. The mixtures increased the aboveground biomass, the root biomass was reduced, so that the root-to-shoot biomass ratio (R:S) and root respiration of the mixtures were lower than that of the monocultures (P<0.05). For CW, the rate of leaf photosynthesis and leaf water use efficiency (WUEleaf) both decreased in mixture compared to the values in the monocultures. When the proportion in the mixture was the same, the rate of photosynthesis of the flag leaf and WUEleaf of PL was significantly greater than CW. In 2006, the root biomass in the PL5:CW5 mixture decreased by 29% and 17% (P<0.01) in the upper soil layer (0–0.4m) and increased by 70% and 99% (P<0.01) in the deep soil layer (0.6–1.0m) in PL and CW, respectively, compared with the individual cultivars in pure stand. The mixtures had reduced water use before stem elongation, but increased water use from deep soil layers after anthesis. These results indicate that under unfavorable conditions, mixtures offer benefits in conserving soil water before stem elongation, and may provide opportunity for greater niche exploitation and more effective resource use efficiency, especially the extraction of water deep in the soil profile. We suggest that the use of a mixture of cultivars in a serious drought season will ensure greater availability of water after stem elongation stage, resulting in higher yields and WUEg than in cultivars grown as a monoculture.

Foliar Spray of Nitrogen Fertilizer on Raised Bed Increases Yield of Transplanted Aman Rice over Conventional Method

Bed planting with foliar nitrogen fertilizer application of rice production systems is very new, and research on it is still at introductory phase. Influence of foliar application of nitrogen fertilizer on growth and yield of transplanted aman rice and evaluation of water and fertilizer application efficiency of rice-fallow-rice cropping system were investigated under raised bed cultivation method. Results showed that foliar spray in bed planting method increased grain yield of transplanted aman rice up to 9.33% over conventional method. Foliar nitrogen fertilizer application in bed planting method increased the number of panicle m−2, number of grains panicle−1, and 1000-grain weight of rice than the conventional method. Sterility percentage and weed infestation were lower at foliar nitrogen fertilizer application in bed planting method than the conventional method. Thirty-nine percent of irrigation water and time for application could be saved through foliar nitrogen spray in bed planting than conventional method. Water use efficiency for grain and biomass production was higher by foliar nitrogen fertilizer application in bed planting than conventional method. Likewise, agronomic efficiency of foliar nitrogen fertilizer application in bed planting method was higher than the conventional method. This study concluded that foliar nitrogen spray in bed planting method is a new approach to get fertilizer and water use efficiency as well as higher yield compared to existing agronomic practice in Bangladesh.

β-Aminobutyric acid increases abscisic acid accumulation and desiccation tolerance and decreases water use but fails to improve grain yield in two spring wheat cultivars under soil drying.

A pot experiment was conducted to investigate the effect of the non-protein amino acid, β-aminobutyric acid (BABA), on the homeostasis between reactive oxygen species (ROS) and antioxidant defence during progressive soil drying, and its relationship with the accumulation of abscisic acid (ABA), water use, grain yield, and desiccation tolerance in two spring wheat (Triticum aestivum L.) cultivars released in different decades and with different yields under drought. Drenching the soil with 100 µM BABA increased drought-induced ABA production, leading to a decrease in the lethal leaf water potential (Ψ) used to measure desiccation tolerance, decreased water use, and increased water use efficiency for grain (WUEG) under moderate water stress. In addition, at severe water stress levels, drenching the soil with BABA reduced ROS production, increased antioxidant enzyme activity, and reduced the oxidative damage to lipid membranes. The data suggest that the addition of BABA triggers ABA accumulation that acts as a non-hydraulic root signal, thereby closing stomata, and reducing water use at moderate stress levels, and also reduces the production of ROS and increases the antioxidant defence enzymes at severe stress levels, thus increasing the desiccation tolerance. However, BABA treatment had no effect on grain yield of wheat when water availability was limited. The results suggest that there are ways of effectively priming the pre-existing defence pathways, in addition to genetic means, to improve the desiccation tolerance and WUEG of wheat.

DROUGHT STRESS: Soil Water Availability Alters the Inter‐ and Intra‐Cultivar Competition of Three Spring Wheat Cultivars Bred in Different Eras

AbstractCompetition for water generates a classic aspect of the tragedy of the commons, the ‘race for fish’, where crops must allocate more resource to acquisition of the limiting resource than is optimal for crop yield allocation. A pot experiment using a simple additive (target–neighbour) design was conducted to examine the above‐ground and below‐ground growth of three spring wheat (Triticum aestivum L.) cultivars when grown alone and in mixtures at three levels of water availability. The effects of competition and water availability were compared by observing patterns of growth, biomass allocation and below‐ground outcomes. Competitive interactions were investigated among cultivars ‘HST’, ‘GY602’ and ‘LC8275’, target plant of each cultivar grown without neighbouring plants are referred to herein as control plant and one target plant of each cultivar sown surrounded either by same or another cultivar as intra‐ or inter‐cultivar competition. Competitive ability was assessed as the response ratio (lnRR) between the target plant surrounded by six other plants and the target plant in isolation. Our results showed that the cultivar ‘HST’, released over a century ago, produced a higher biomass and grain yield than the more recently released cultivars ‘LC8275’ and ‘GY602’ when grown as isolated plants with sufficient water supply. However, competition for resources from neighbours led to target plant biomass and grain yield being significantly reduced relative to controls in all three cultivars, particularly in ‘HST’. When subjected to intra‐cultivar competition, the two recently released cultivars ‘LC8275’ and ‘GY602’ had higher grain yields and water use efficiency for grain than ‘HST’ in all three water regimes. The landrace ‘HST’ had better and significantly linear relationships between biomass and biomass allocation, root length and specific root length, whereas the recent and modern cultivars had much more water‐related species‐specific changes in root morphology and allocation patterns. These results suggest that crop traits that influence competitive ability, such as biomass allocation to roots and root plasticity in response to drought have changed in modern wheat cultivars because of breeding and selection.

Influence of row spacing on water use and yield of rain-fed wheat (Triticum aestivum L.) in a no-till system with stubble retention

A 3-year field study was undertaken to investigate the effect of row spacing on vegetative growth, grain yield and water-use efficiency of wheat. All 3 years of the study experienced 21–51% below-average rainfall for the growing season. Widening row spacing led to reduced biomass and tillers on per plant basis which could be related to the reduction in light interception by the wheat canopy in the wide rows which in turn could have reduced assimilate production. Reduction in vegetative growth in 54-cm rows translated into a significant reduction in grain yield which was strongly associated (r2 = 0.71) with the loss of spike density. The pattern of crop water use (evapotranspiration, ET) during the growing season was very similar for the three row-spacing treatments. However, there was some evidence for slightly lower ET (~5%) in 54-cm rows in two growing seasons. More importantly, there was no evidence for increased ET during the post-anthesis phase in wide rows as has been speculated by some researchers. Over the 3 years of the study, grain yield declined by 5–8% as row spacing increased from 18 to 36 cm and by a further 12–20% as row spacing increased from 36 to 54 cm. There was a consistent decline in water-use efficiency for grain (WUEG) with increasing row spacing over the 3 years. WUEG declined by 6–11% as crop spacing increased from 18 to 36 cm and declined further by 12–15% as row spacing increased to 54 cm. Lower light interception at wider row spacing could have reduced assimilate production by wheat as well as increased soil evaporation due to lower shading of the soil surface in more open canopies. Growers adopting wider row spacing on these relatively heavy textured soils are likely to experience some reduction in grain yield and WUEG. However, some growers may be prepared to accept a small yield penalty from intermediate row spacing as a trade-off for increased stubble retention and soil health.

Soil water availability and plant competition affect the yield of spring wheat

This study was conducted to determine the effect of both inter-cultivar and intra-cultivar competition on the growth of three spring wheat ( Triticum aestivum L.) cultivars released in different periods that had different root:shoot ratios, differed in water extraction from dry soil, and differed in height. Two water regimes were imposed to compare competitive effects under irrigated and rainfed conditions. Our main hypotheses were that the different distribution of biomass between shoot and root in old and new wheat cultivars will alter their competitive ability, that differences in root size will alter their competitive ability through different water uptake patterns, and differences in the gradient for water uptake will alter their competitive ability in different environments by enabling water extraction from drier soil. In monoculture, the recent cultivars had significantly more grain yield and higher water use efficiency for grain (WUE G) than the old cultivar. Under the two water regimes the old cultivar had more root biomass, and extracted water in deeper soil layers, whereas the modern cultivars extracted more water in dry soil layers. The old cultivar benefited from inter-cultivar competition in terms of both grain yield and above-ground biomass accumulation at the expense of the modern cultivars, which showed significantly reduced growth in mixtures compared to in monoculture. Our study suggested that the below-ground competitive ability of cultivars may have a negative relationship with the grain yield and WUE G in monoculture. The yield superiority of modern and recent cultivars was mostly due to increased above-ground biomass, kernel number and WUE G and a smaller proportion of root biomass. Our results demonstrate that inter-plant competition is an important factor affecting spring wheat productivity in contrasting environments, but the extent and intensity of these effects depend on the adaptation of root traits to available soil water. Reducing root growth redundancy and enhancing the ability to deplete more soil water are clearly adaptive features for wheat for water-limited conditions.

How two ridges and the furrow mulched with plastic film affect soil water, soil temperature and yield of maize on the semiarid Loess Plateau of China

Plastic film mulching is an effective practice to improve water harvest and crop productivity in semiarid areas. The grain yield of maize ( Zea mayis) as affected by various mulching practices was studied in the field in 2006 and 2007 to determine a mulching pattern that would increase rainwater harvest and crop yield. In 2006, three treatments were used: (1) flat plot without mulch (CK); (2) two ridges and furrows mulched by one plastic film and maize planted in the furrow between the two ridges (DRM); (3) two rows of maize planted in a ridged bed mulched with plastic (RM). Two additional treatments were tested in 2007: (4) two rows of maize mulched with a 70-cm wide plastic film and then 30 cm of bare soil alternated (NM); (5) maize planted without ridges in double rows 80 cm apart and the whole plot mulched with plastic film (WM). Maize yield was highest in the DRM treatment: 1150 kg ha −1 in 2006 and 6130 kg ha −1 in 2007. This was associated with better topsoil moisture in the planting zone and higher soil temperature in the DRM treatment compared with the other treatments. The soil moisture in DRM reached 10.5% and 22.6%, in 2006 and 2007, respectively, the highest of all the treatments. The mean temperature in DRM was higher than in CK and RM by 1.2 °C and 0.4 °C, respectively in 2006, while in 2007, it was higher than that in CK by 3.1 °C, in RM by 0.6 °C, in NM by1.7 °C and in WM by 0.6 °C in 2007. The higher temperatures in the DRM treatments resulted in the maize maturing earlier than in the other mulched treatments, 15 days earlier than in RM in 2006 and 11 days, 3 days, and 14 days earlier than in RM, WM, and NM, respectively in 2007. The highest water-use efficiency (WUE) was found in DRM in both years. In 2006, the WUE in DRM was six times greater than that in CK and 9.96% greater than in RM. In 2007, the WUE for grain in the DRM treatment was 16.6 kg ha −1 mm −1, 11 times greater than that in CK and greater than RM, NM and WM by 67.7%, 26.7% and 9.2%, respectively. It is concluded that the double ridges and furrow mulching treatment could serve as a model for maize production for small-holder farmers in semiarid regions.

Carbon isotope discrimination and water use efficiency in Iranian diploid, tetraploid and hexaploid wheats grown under well-watered conditions

Carbon isotope discrimination (Δ) has been proposed as physiological criterion to select C3 crops for yield and water use efficiency. The relationships between carbon isotope discrimination (Δ), water use efficiency for grain and biomass production (WUEG and WUEB, respectively) and plant and leaf traits were examined in 20 Iranian wheat genotypes including einkorn wheat (Triticum monococcum L. subsp. monococcum) accessions, durum wheat (T. turgidum L. subsp. durum (Desf.) Husn.) landraces and bread wheat (T. aestivum L. subsp. aestivum) landraces and improved cultivars, grown in pots under well-watered conditions. Carbon isotope discrimination was higher in diploid than in hexaploid and tetraploid wheats and was negatively associated with grain yield across species as well as within bread wheat. It was also positively correlated to stomatal frequency. The highest WUEG and grain yield were noted in bread wheat and the lowest in einkorn wheat. Einkorn and bread wheat had higher WUEB and biomass than durum wheat. WUEG and WUEB were significantly negatively associated to Δ across species as well as within bread and durum wheat. The variation for WUEG was mainly driven by the variation for harvest index across species and by the variation for Δ within species. The quantity of water extracted by the crop, that was closely correlated to root mass, poorly influenced WUEG. Environmental conditions and genetic variation for water use efficiency related traits appear to highly determine the relationships between WUEG and its different components (water consumed, transpiration efficiency and carbon partitioning).