A straw mulch system to allow continuous wheat production in an arid climate

Cereal Cyst Nematode (CCN, Heterodera avenae Woll.) has been shown to be a devastating pest for wheat (Triticum aestivum L.) in dryland regions. Fallowing in the season preceding the cropping season has been hypothesized to sanitize the soil of CCN and allow wheat production. This paper explores management options that might allow the continuous production of wheat in these regions. In a 20-year study in the Negev, Israel, on a sandy loam, loessial, soil, it was found that in those seasons with high rainfall there was virtually no decrease in annual wheat yields for continuous crops as compared to biennial fallow yields obtained with the conventional wheat system. The hypothesis that high soil water content substantially alleviates the damage resulting from CCN infestation was confirmed in a pot study. A practical solution for maintaining high soil water content in the field was to leave a straw mulch on the soil surface to decrease soil evaporation. A chopper was added to a grain harvester to finely chop the straw so that it settles to the soil surface through the stubble, and a no-till drill was used for sowing through the straw. The straw-mulch system was shown to result in annual yields from continuous wheat that were equivalent to yields in alternate years with the conventional fallow wheat system, thereby doubling wheat production in this dryland region.     

Model analysis of a straw mulch system for continuous wheat in an arid climate

Wheat (Triticum aestivum L.) production in some dryland regions is severely limited by the cereal cyst nematode (Heterodera avenae Woll.). Conventional fallow management during a wet period has been shown to allow hatching of the cysts during the fallow season and thereby sanitize the soil for the subsequent wheat crop. Recently a straw mulch (SM) management has been introduced into a long-term experiment in the Negev region of Israel. This management ameliorated the nematode damage and allowed continuous wheat production. Only three seasons of successful experimentation exist with the SM system so questions remain about its performance over seasons with differing weather conditions. A simple, mechanistic, wheat model was extended to simulate wheat development and growth when the crop is grown on nematode-infested soils. Incorporating statements describing inhibition of rooting depth as a result of nematode activity resulted in good agreement between simulations and 16 seasons of yield observations on continuous wheat. The effect of SM was simulated simply by decreasing soil evaporation and this resulted in higher levels of soil water and decreased nematode inhibition of rooting. Good agreement was obtained between the three seasons of experimental data and simulations of the SM system, with predicted grain yield within 10% of observations. Over 16 seasons, simulations of the SM system indicated substantial grain yield increases over continuous wheat in all but the highest-yielding season. Simulations in 14 seasons with conventional fallow management revealed that annual yields of SM were equivalent to biennial yields of the fallow system, resulting in a predicted doubling of wheat production for this dryland region of the Negev.     

Effect of lowering the root/shoot ratio by pruning roots on water use efficiency and grain yield of winter wheat

A pot and a field experiment were conducted to assess the effects of root/shoot ratio (R/S) on the water use efficiency (WUE) and grain yield of winter wheat. The R/S was regulated by pruning the roots during the stem elongation stage, resulting in reduced root systems of the plants. At the heading stage, the root dry weight of root-pruned plants was less than that of intact-root plants, but their R/S was similar to that of intact-root plants under both experimental conditions. After tiller pruning, the R/S of root-pruned plants was significantly lower than that of intact-root plants (p < 0.05). Root pruning reduced the rate of leaf transpiration and lowered the number of tillers per plant (p < 0.05) during the vegetative stage. As a result, root-pruned wheat showed reduced water use when compared to intact-root plants before heading (p < 0.05). At anthesis, there was no significant difference in transpiration between plants with intact roots and those with pruned roots in the pots. However, under field conditions, transpiration of root-pruned plants was significantly higher than that of intact-root plants at anthesis. Additionally, at anthesis root-pruned plants had a higher rate of leaf photosynthesis and lower rate of root respiration, which resulted in a significantly higher grain yield at maturity when compared to plants with intact roots. Under both experimental conditions, there were no significant differences in shoot dry weight per plant between root-pruned and intact-root plants grown in monoculture. When root-pruned plants were grown with intact-root plants, the root-pruned wheat was less productive and had a lower relative shoot dry weight (0.78 and 0.86, respectively) than the intact-root plants (1.24 and 1.16, respectively). These results suggest that plants with pruned roots had a lower ability to compete and to acquire and use the same resources in the mixture when compared with intact-root plants. Root pruning improved the WUE of winter wheat under both experimental conditions. This suggests that appropriate management for the root system/tillers in wheat crops can be used to increase grain yield and water use efficiency. Specifically, lowering the R/S improved the grain yield and WUE of winter wheat significantly by lowering its competitive ability and improving root efficiency. Therefore, drought-resistance breeding to improve the grain yield and WUE, at least for wheat, should be made by targeted selection of less competitive progeny with a small R/S for cultivation in arid and semiarid areas.     

Root size,distribution and soil water depletion as affected by cultivars and environmental factors

Field experiments were carried out in two parts at the Luancheng Experimental Station in the North China Plain. Part I, which was a continuous experiment that ran from 1990 to 2008, investigated the change of grain yield, evapotranspiration (ET), root size and soil water utilization of winter wheat (Triticum aestivum L.) under three water regimes (rain-fed, two and four irrigation applications). Part II used 10 cultivars released from 1970 to 2000 that were grown under the same condition for two seasons (2005/2006 and 2006/2007) to compare root size, root:shoot ratio and soil water depletion (SWD). The results of testing in Part I showed that the yield and ET of winter wheat gradually increased from 1990 to the present. There was no consistent change in total root length (TRL) over time. The difference in root size among seasons and irrigation treatments mainly occurred in the upper soil profile, where the root length density (RLD) was greater. No direct relationship was found between root size and soil water use. Thus, TRL was not a factor that indicated the water extracting capacity of crops. The results from Part II revealed that the seasonal ET of earlier released cultivars (ERC) was similar to that of recently released cultivars (RRC) under well-watered conditions. However, ET was slightly increased from ERC to RRC under water deficit conditions, indicating high soil water depletion by RRC. TRL decreased from ERC to RRC and was significantly correlated with plant height. The breeding of winter wheat that reduced plant height not only increased harvest index, but also reduced root size, resulting in a smaller root:shoot ratio. The reduction in TRL from ERC to RRC mainly occurred in the top soil profile. The results from both tests indicate that TRL is not a factor that determines soil water use; rather, the distribution of RLD along the soil profile plays more important role in soil water utilization. Smaller root size in the upper soil layer did not affect soil water uptake, and might be more economical in terms of production efficiency.     

Short‐term soil quality response to forage species and pH

Forages are important throughout the south‐east USA for livestock production and wildlife habitat. However, little is known about how forage species commonly grown in this region influence soil‐quality indicators. The objectives of this research were to determine short‐term response of soil water‐stable aggregates (WSA) and density of fungal hyphae (DFH) to: (i) forage species or mixtures grown at identical soil pH levels and (ii) forage species or mixtures grown at field‐state versus adjusted soil pH levels. Nine warm‐season species (sole crop) and eleven cool‐season sole crop or legume–grass mixtures were grown under protected culture in southern coastal plain soil microcosms. Levels of WSA and DFH, and plant shoot and root biomass were evaluated after two 12‐week experimental growth periods in both field‐state and adjusted‐pH soil. Both warm‐ and cool‐season forage species significantly altered short‐term responses of WSA and DFH levels; these responses differed when the soil pH was adjusted from the field state with lime addition. The short‐term responses of both WSA and DFH to lime addition in coastal plain soil were negative only when certain forage species were grown, and no response was detected for the control. It appeared that differences in plant shoot and root developmental characteristics played a key role in soil WSA and DFH responses to the species studied. Further long‐term studies are needed to understand how these relationships are expressed in more variable environments over expanded time frames.     

底墒对冬小麦植株生长及产量的影响

设计5种不同底墒处理,结合冬小麦苗期控水、抽穗复水的人工干预,通过钻取0~200cm根系样本和生育期内连续观测最大根深,对应分析地上部生物量及产量因素,以了解底墒通过调控根系在土壤中的垂直分布和土壤水分的利用对冬小麦地上植株生长发育和产量形成的影响。底墒充足时诱导根系相对较多地向土壤纵深下扎,形成了上层相对较少、深层相对较多的根系构型,其0~30cm浅层根系生物量占0~200cm整层比例较底墒较差的处理少10.95个百分点,而100~200cm深层偏多5.70个百分点,延深了根系汲取土壤水分的深度,而且底墒在冬小麦全生育期中持续发挥着水分调节作用。底墒充足时收获指数、水分利用效率(WUE)都最高,其收获指数为0.4920,WUE为1.5479g/(m2·mm),分别比底墒较差的处理偏高0.0823和0.3030g/(m2·mm)。     

返青期断根对秸秆覆盖冬小麦产量及叶片光合特性的影响

为了解返青期断根对黄土高原旱地保护性耕作下小麦产量形成及水分利用的调控作用,在陕西长武县开展旱地秸秆覆盖条件下冬小麦返青期断根试验,分析了返青期断根对冬小麦籽粒产量、地上部生物量、收获指数、产量构成三要素、拔节期群体数量、生育期耗水量、水分利用效率、花后旗叶光合特性及衰老特性的影响。结果表明,返青期断根对冬小麦地上部生物量、穗数、粒重和生育期耗水量没有显著影响。与CK(不断根)相比,返青期断根后冬小麦拔节期总茎数减少了11.9%,开花期叶面积指数、花后旗叶叶绿素含量、光合速率和蒸腾速率提高,分蘖成穗率、穗粒数、籽粒产量、收获指数和水分利用效率分别增加了14.1%、10.5%、8.2%、10.4%、17.5%和20.4%。这说明返青期断根可促进秸秆覆盖条件下冬小麦分蘖成穗,增加花后旗叶光合作用,改善穗部结实特性,提高籽粒产量和水分高效利用。     

施肥对水分胁迫下冬小麦根系提水及养分利用的影响

为了解水分胁迫下施肥对冬小麦根系提水及养分利用的影响以及水肥在小麦生长过程中的协同效应,采用两室分根土培方法,通过对上下两个土层（上层：0~20 cm;下层：20~60 cm）含水量进行控制和观测,分析了不同水分处理间小麦根系提水量、养分积累和表现利用率的差异。结果表明,在土壤上干下湿（DW）条件下冬小麦系提水作用明显,施肥处理对冬小麦全生育期根系提水量有明显影响,表现为氮磷配施、单施磷>对照（不施肥）>单施氮。在氮磷配施条件下,小麦植株及各器官氮磷养分累积量高于其他施肥处理（单施磷、对照和单施氮）,各施肥条件下植株氮磷素累积量均表现为WW>DW>DD。氮磷肥表观利用率明显高于单施氮或单施磷处理,且表现出DW和WW（上下土层均湿润）处理的氮磷肥表观利用率均高于DD水分处理（上下土层均干燥）。由此可见,氮磷配施可明显提高水分胁迫（DW）下小麦根系从土壤深层的提水作用,同时促进植株对氮磷养分的积累和利用,实现水肥相互协同。     

Upland rice grown in soil-filled chambers and exposed to contrasting water-deficit regimes: II. Mapping quantitative trait loci for root morphology and distribution

Root morphological characteristics are known to be important in the drought resistance of some rice (Oryza sativa L.) varieties. The identification of quantitative trait loci (QTLs) associated with root morphology and other drought resistance-related traits should help breeders produce more drought resistant varieties. Stability in the expression of root growth QTL across rooting environments is critical for their use in breeding programs. A greenhouse experiment in which a mapping population of 140 recombinant inbred lines and the parental varieties Bala and Azucena were grown in glass-sided soil chambers and evaluated for root growth and water uptake was conducted. In each of 2 years, two treatments were used; an early water-deficit (WD0) in which seeds were sown into wet soil but received no more water, and a late water-deficit (WD49) in which the plants were watered for 49 days and then received no water for a week. The major differences between treatments and years in dry matter partitioning and root growth traits are reported elsewhere. Here, the identification of QTLs for root growth traits by composite interval mapping is described. At LOD>3.2, there were six QTLs for the weight of roots below 90 cm and maximum root length, 11 for root to shoot ratio, 12 for the number of roots past 100 cm, and 14 for root thickness. A total of 24 regions were identified as containing QTLs (these regions often contained several QTLs identified for different root traits). Some were revealed only in individual experiments and/or for individual traits, while others were common to different traits or experiments. Seven QTLs, on chromosomes 1, 2, 4, 7, 9 (two QTLs) and 11, where considered particularly noteworthy. The complex results are discussed in the context of previously reported QTLs for root growth in other populations, the interaction between QTL with the environment and the value of QTLs for breeding.     

Responses of Root Growth to Moderate Soil Water Deficit in Wheat Seedlings

Abstract

In the field, plants show better root growth in drying soil than in wet soil. However, the root growth enhancement has not been demonstrated clearly in the laboratory. In this study, the root growth response of wheat seedlings to moderate soil water deficits was characterized quantitatively in an environment-controlled chamber. Germinated seeds of wheat were grown for 15 days in the soil with a water potential ranging from field capacity (FC) to approximately –0.08 MPa. Theleaf area decreased with reduction in soil water potential. By contrast, the root surface area increased upon reduction ofthe soil water potential to –0.04 MPa while it decreased significantly in soil with a water potential of –0.08 MPa. The increase in surface area was obvious in the roots with a diameter of 0.2 to 0.4 mm and larger than 0.7 mm. Root weight increased with the reduction of soil water potential to –0.04 MPa. While specific root length decreased significantly with the reduction of water potential to –0.06 MPa, the specific root surface area did not. Assimilatestransported from shoot might be used in roots to increae the surface area mainly by increasing the diameter rather than the length in response to a moderate soil water deficit in wheat seedlings. This might result from the drought tolerance mechanism of osmotic adjustment in roots.     

Cropping sequence and tillage system influences annual crop production and water use in semiarid Montana,USA

Available water is typically the biggest constraint to spring wheat production in the northern Great Plains of the USA. The most common rotation for spring wheat is with summer fallow, which is used to accrue additional soil moisture. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, allowing for increased cropping intensity. We conducted a field trial from 1998 through 2003 comparing productivity and water use of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average most years, resulting in substantial drought stress to crops not following fallow. Preplant soil water, water use, and spring wheat yields were generally greater following summer fallow than wheat recropped after wheat or alternate crops. Water use and yield of wheat following summer fallow was greater than for chickpea or yellow mustard, the only other crops in the trial that followed summer fallow. Field pea performed best of all alternate crops, providing yields comparable to those of recropped spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region, at least during periods of below average precipitation. Following summer fallow, and despite drought conditions, zero tillage often provided greater amounts of soil water at planting compared to conventional tillage.     

Modeling responses of dryland spring triticale,proso millet and foxtail millet to initial soil water in the High Plains

Dryland farming strategies in the High Plains must make efficient use of limited and variable precipitation and stored water in the soil profile for stable and sustainable farm productivity. Current research efforts focus on replacing summer fallow in the region with more profitable and environmentally sustainable spring and summer crops. In the absence of reliable precipitation forecasts for the crop growing season, farmers rely mainly upon knowledge of plant available water (PAW) in the soil profile at planting for making crop choice decisions. To develop a decision support strategy for crop selection based on initial PAW, experiments were conducted with spring triticale (XTiticosecale Wittmack), proso millet (Panicum miliaceum L.), and foxtail millet (Setaria italica L. Beauv.) under artificially controlled Low, Medium, and High initial PAW levels during 2004 and 2005 at Akron, Colorado, and Sidney, Nebraska. The objectives of this study were to adapt an existing cropping systems model for the simulation of triticale and millet and to evaluate simulations from the adapted model by comparing results with field data collected under varying initial PAW conditions. The Root Zone Water Quality Model with DSSAT v4.0 crop growth modules (RZWQM2) was used. Specifically, the Cropping System Model (CSM)–CERES–Wheat module was adapted for simulating triticale, and CSM–CERES–Sorghum (v4.0) module was adapted for simulating proso millet and foxtail millet. Soil water, leaf area index, grain yield, and biomass data for the highest PAW treatment from one crop season for each of the three crops were used to adapt and calibrate the crop modules. The models were then evaluated with data from the remaining PAW treatments. The proso millet module was further tested with four years of data from a crop rotation experiment at Akron from 2003 to 2006. Simulation results indicated that the adapted and calibrated crop modules have the potential to simulate these new crops under a range of varying water availability conditions. Consequently, these models can aid in the development of decision support tools for the season-to-season management of these summer fallow replacement crops under dryland conditions in semi-arid environments.     

土壤干旱对冬小麦水分生理和生物量分配的影响

为了明确土壤长期持续干旱对冬小麦生理状况和生长发育的影响,采用盆栽方法,对长期持续不同土壤干旱条件下冬小麦水分生理和生物量的分配进行了初步研究。结果表明,随土壤水分的减少,冬小麦蒸腾速率、叶水势、叶片相对含水率、耗水量、耗水系数等水分生理指标均呈降低趋势,饱和亏呈递增趋势;地上部干物质量和总干重递减,根系量除轻度干旱处理最大外,其他各处理递减,根冠比递增。这说明,冬小麦随土壤水分的减少抗旱性增强,低土壤水分有利于增大光合产物向根系的分配,高土壤水分则有利于地上部发育。     

Rooting systems of oilseed and pulse crops. II: Vertical distribution patterns across the soil profile

Root distribution patterns in the soil profile are the important determinant of the ability of a crop to acquire water and nutrients for growth. This study was to determine the root distribution patterns of selected oilseeds and pulses that are widely adapted in semiarid northern Great Plains. We hypothesized that root distribution patterns differed between oilseed, pulse, and cereal crops, and that the magnitude of the difference was influenced by water availability. A field experiment was conducted in 2006 and 2007 near Swift Current (50°15′N, 107°44′W), Saskatchewan, Canada. Three oilseeds [canola (Brassica napus L.), flax (Linum usitatissimum L.), mustard (Brassica juncea L.)], three pulses [chickpea (Cicer arietinum L.), field pea (Pisum sativum L.), lentil (Lens culinaris)], and spring wheat (Triticum aestivum L.) were hand-planted in lysimeters of 15 cm in diameter and 100 cm in length which were pushed into soil with a hydraulic system. Crops were evaluated under low- (natural rainfall) and high- (rainfall + irrigation) water conditions. Vertical distribution of root systems was determined at the late-flowering stage. A large portion (>90%) of crop roots was mainly distributed in the 0-60 cm soil profile and the largest amount of crop rooting took place in the top 20 cm soil increment. Pulses had larger diameter roots across the entire soil profile than oilseeds and wheat. Canola had 28% greater root length and 110% more root tips in the top 10 cm soil and 101% larger root surface area in the 40 cm soil under high-water than under low-water conditions. In 2007, drier weather stimulated greater root growth for oilseeds in the 20-40 cm soil and for wheat in the 0-20 cm soil, but reduced root growth of pulses in the 0-50 cm soil profile. In semiarid environments, water availability did not affect the vertical distribution patterns of crop roots with a few exceptions. Pulses are excellent “digging” crops with a strong “tillage” function to the soil due to their larger diameter roots, whereas canola is more suitable to the environment with high availability of soil water that promotes canola root development.     

Effect of temperature and water variables on the juvenile growth of lucerne and red clover

Plants of three cultivars of lucerne ( Medicago sativa L.) and of red clover ( Trifolium pratense L.) were grown at four levels each of water availability and temperature in all combinations to evaluate these factors as determinants of plant growth. Plants grew in conventional plant growth chambers from age 2 to 4 weeks with the roots held between layers of polyester cloths that held a volume of nutrient solution which was adjusted at 24-h intervals by flushing and blotting the cloths. The experimental design consisted of two growth chamber runs at each of four temperatures. Within each run, water treatments and the species-cultivar combination were arranged In four replicates of a split-plot design with water treatment as whole plot and species-cultivars as subplots.
Plant response variables over all treatments were significant (P < 0·05) for temperature and water for shoot weights, root weights, shoot/root ratios and number of roots. Cultivars within species had no significant difference in response lo the treatments, but species differences were significant for alt response variables except shoot/root ratio.     

Physiological Response of Three Wheat Cultivars to High Shoot and Root Temperatures during Early Growth Stages

Abstract

Understanding wheat (Triticum aestivum L.) response to high shoot/root temperature during the early growth stages is important for successful production in tropical and subtropical environments. This study examined the physiological response of wheat cultivars to high shoot and/or root temperatures during early growth stages. Three cultivars; Imam, Fang and Siete Cerros were grown in soil and hydroponically at three shoot/root temperatures (23/23, 23/35 and 35/35ºC for the soil experiment; and 22/22, 22/38 and 38/38ºC for the hydroponic experiment). Leaf dry weight and leaf area plant-¹ were significantly decreased by high shoot/ root temperature (HS/HR, 35/35 and 38/38ºC) but was not affected by a normal shoot/high root temperature (NS/HR, 23/35 and 22/38ºC). The NS/HR (22/38ºC) and HS/HR (38/38ºC) treatments in the hydroponic experiment significantly decreased photosystem II quantum yield ( Φ_psii), photosynthetic rate (P_n) and specific leaf area (SLA) compared with the normal shoot/normal root (NS/NR, 22/22ºC) temperature treatment. Chlorophyll accumulation was significantly decreased by NS/HR, but increased significantly by HS/HR in most of the measuring dates. The heat-tolerant cultivar, Fang, always had the highest chlorophyll content, Φpsii and P_n under all temperature treatments, while the heat-sensitive cultivar, Siete Cerros, always had the greatest reduction in these traits especially towards the end of the experiment. Imam and Fang responded to HS/HR in the hydroponic experiment by immediate and greater reductions in leaf dry weight, total leaf area and SLA during the first wk of the treatments compared with Siete Cerros. The response changed with the treatments duration such that Imam showed the least reduction and Siete Cerros was the most affected cultivar towards the end of the experiment. Thus, wheat cultivars differentially responded to high shoot/root temperature by reducing the leaf weight and area and hence accumulating more chlorophyll in the diminished leaves. The failure to undergo such changes led to significantly lower chlorophyll accumulation, Φ_psii and P_n under high root temperature.     

Effect of season and cutting frequency on root and shoot competition between Festuca pratensis and Dactylis glomerata

Abstract Plant competition strongly affects the species composition of managed grassland. To identify relevant processes, Festuca pratensis (Huds.) and Dactylis glomerata (L.) were grown as monocultures or mixtures in boxes placed in the field for two seasons and subjected to two cutting frequencies. Root and shoot competition effects were separated using soil and aerial partitions. Shoot competition was analysed by measuring the vertical distribution of the leaf area and root competition by analysing the absorption of tracers. Values of relative yield indicated that the two grasses fully competed for the same limiting resources under the experimental conditions. The competitive ability of F. pratensis was lower during both years relative to D. glomerata. This was mainly related to its consistently lower shoot competitive ability, which was associated with less leaf area in the upper layers of the canopy and shorter leaves. Root competitive ability of F. pratensis changed with season. It was similar to that of D. glomerata during spring and autumn, but less during summer. The lower root competitive ability in summer might be due to the lower root activity of F. pratensis, measured as rubidium (Rb) and strontium (Sr) absorption in July, 0·1 and 0·2 m below the ground. Cutting frequency did not greatly influence the relative importance of root and shoot competition during the first growing season. However, under infrequent defoliation, the competitive ability of F. pratensis decreased markedly in full competition during the second growing season. These results suggest that distinct differences in the canopy structure and root activity of different plant species can affect the relative importance of root and shoot competition during the season.     

Rooting systems of oilseed and pulse crops I: Temporal growth patterns across the plant developmental periods

Oilseed and pulse crops have been increasingly used to diversify cereal-based cropping systems in semiarid environments, but little is known about the root characteristics of these broadleaf crops. This study was to characterize the temporal growth patterns of the roots of selected oilseed and pulse crops, and determine the response of root growth patterns to water availability in semiarid environments. Canola (Brassica napus L.), flax (Linum usitatissimum L.), mustard (Brassica juncea L.), chickpea (Cicer arietinum L.), field pea (Pisum sativum L.), lentil (Lens culinaris), and spring wheat (Triticum aestivum L.) were tested under high- (rainfall + irrigation) and low- (rainfall only) water availability conditions in southwest Saskatchewan, in 2006 and 2007. Crops were hand-planted in lysimeters of 15 cm in diameter and 100 cm in length that were installed in the field prior to seeding. Roots were sampled at the crop stages of seedling, early-flower, late-flower, late-pod, and physiological maturity. On average, root length density, surface area, diameter, and the number of tips at the seedling stage were, respectively, 41, 25, 14, and 110% greater in the drier 2007 than the corresponding values in 2006. Root growth in all crops progressed rapidly from seedling, reached a maximum at late-flower or late-pod stages, and then declined to maturity; this pattern was consistent under both high- and low-water conditions. At the late-flower stage, root growth was most sensitive to water availability, and the magnitude of the response differed between crop species. Increased water availability increased canola root length density by 70%, root surface area by 67%, and root tips by 79% compared with canola grown under low-water conditions. Water availability had a marginal influence on the root growth of flax and mustard, and had no effect on pulse crops. Wheat and two Brassica oilseeds had greater root length density, surface area and root tips throughout the entire growth period than flax and three pulses, while pulse crops had thicker roots with larger diameters than the other species. Sampling roots at the late-flower stage will allow researchers to capture best information on root morphology in oilseed and pulse crops. The different root morphological characteristics of oilseeds, pulses, and wheat may serve as a science basis upon which diversified cropping systems are developed for semiarid environments.     

Simulated long-term effects of different soil management regimes on the water balance in the Loess Plateau, China

A soil management regime that improves water use efficiency (WUE) is urgently required to increase the sustainability of the winter wheat-summer fallow system in the Loess Plateau, China. However, the long-term partitioning of the water balance must be understood in order to evaluate the viability of possible soil management regimes. Therefore, an ecosystem model (CoupModel) was used to explore the effects on components of the water balance of five types of soil management regimes: conventional practice, wheat straw mulching, incorporation of high organic matter contents, compaction, and use of a harvested fallow crop. Three variants of the fallow crop approach were also considered, in which the crop was harvested 15, 30 and 45 days before sowing the wheat (designated Fallow-15d, Fallow-30d and Fallow-45d, respectively). Simulations were used to identify the relative magnitude of soil evaporation, wheat transpiration and deep percolation and to elucidate the temporal variability in these components for a selected location using climate records spanning 45 years. However, the soil management regime significantly influenced the magnitude of every component of the water balance (in terms of minimum, maximum and mean values) over the long periods considered. Consequently, wheat yield and WUE differed significantly among the simulated treatments. Mulching led to significantly lower soil evaporation, higher transpiration, and more frequent and extensive deep percolation than other regimes, thereby improving fallow efficiency (percentage of rainfall stored in the soil during the fallow period at the end of the fallow period), wheat yields and WUE. In contrast, soil compaction gave the opposite results, leading to the most unfavourable partitioning of the water balance reflected in the lowest wheat yield and WUE values of all the regimes. In 90% of the years no deep percolation occurred in the soil compaction simulations. Use of a fallow crop with optimal harvest timing (Fallow-30d) improved partitioning of the water balance (decreased soil evaporation) and did not significantly reduce wheat yield compared with conventional practice. High organic matter contents in the soil also had a positive influence on the water balance and improved wheat yield and WUE relative to conventional practice. Therefore, mulching appears to be the best management practice for the winter wheat-summer fallow system in the Loess Plateau, according to the simulations. Increasing soil organic matter may be the best option if mulching cannot be implemented. The ideal time for harvesting a fallow crop for use as green manure or fodder appears to be ca. 30 days before sowing the winter wheat.     

Effects of tillage,crop rotation and nitrogen fertilization on wheat-grain quality grown under rainfed Mediterranean conditions

The grain quality of wheat is influenced by the protein content, which in turn depends on environmental conditions and cropping practices. We carried out a 3-year field study in a rainfed Mediterranean region on the effects of tillage, crop rotation and nitrogen fertilization on the grain quality of hard red spring wheat (Triticum aestivum) in terms of protein content, test weight and alveogram indices. Tillage treatments were no tillage (NT) and conventional tillage (CT). Crop rotations were wheat–sunflower (Helianthus annus L.) (WS), wheat–chickpea (Cicer arietinum L.) (WCP), wheat–fababean (Vicia faba L.) (WFB), wheat–fallow (WF) and continuous wheat (CW). Fertilizer nitrogen was used at three different rates: 50, 100 and 150 kg N ha⁻¹. A split–split plot design with four replicates was used. Grain protein content was found to be inversely proportional to rainfall during the growing season. The tillage method was also found to affect grain protein content, test weight and some grain quality indices. Through its effect on moisture and nitrate in the soil. The crop rotations that included a legume (WCP and WFB) had marked effects on wheat quality. The increased grain protein content and resulted in improved rheological properties of the dough (viz. a higher alveogram index and a more balanced tenacity/extensibility ratio). However, no differences due to N dilution in the plant were observed in the wettest year studied, which was also the highest yielding. Increasing the fertilizer N rate increased the grain protein content; this variable had the most marked influence on grain quality indices, though in the year that gave the highest yield the N dilution effect was observed. The many significant interactions among experimental variables reveal a close relationship among grain yield, protein content, grain quality and the wheat growth conditions. Specifically, the amount of rainfall and its distribution in the growing season strongly influenced N availability and uptake by the crop, as well as wheat-grain quality indices.