Wheat Water Use Research Articles

Effects of wheat yield and water use under dual-mulching mode of plastic film and straw in the dryland farming

Effects of wheat yield and water use under dual-mulching mode of plastic film and straw in the dryland farming

Choice of Summer Fallow Replacement Crops Impacts Subsequent Winter Wheat

Winter wheat (Triticum aestivum L.) is the foundation of dryland cropping systems in the Central Great Plains. The objective of this study was to quantify the effects of four short‐season spring‐planted crops used to replace summer fallow on the subsequent winter wheat crop. Wheat was seeded into four crop stubbles [spring triticale (×Triticosecale Wittmack), dry pea (Pisum sativum L.), foxtail millet (Setaria italica L. Beauv.), and proso millet (Panicum miliaceum L.)] at sites near Akron, CO, and Sidney, NE, in the fall of 2004 and 2005. These summer fallow replacement crops were planted into silt loam soils at three different soil water levels at planting (low, medium, and high). Winter wheat water use was 3.6 cm greater, and grain yield was 662 kg ha−1 greater in the high water treatment compared with the low water treatment averaged across all sites and years. Winter wheat used an average of 4.3 cm more water following early planted summer crops (triticale and dry pea) than after late planted summer crops (foxtail and proso millet), but this increased water use did not consistently translate into increased grain yield as a result of terminal drought at Sidney in 2006. The high water treatment always had a positive net return. The high cost of pea seed ($3.30 kg−1, USD) strongly reduced profitability. The flexible summer fallow cropping system appears to be most applicable when using short‐duration summer annual forage crops such as triticale and foxtail millet.

Water fluxes at a fluctuating water table and groundwater contributions to wheat water use in the lower Yellow River flood plain, China

AbstractCapillary upflow from and deep percolation to a water table may be important in crop water supply in irrigated areas of the lower Yellow River flood plain, north China. These fluxes at the water table and the variations of the capillary upflow in relation to crop evapotranspiration need to be investigated to quantify the effect of a water table on soil water balance and to improve agricultural water management. A large weighing lysimeter was used to determine daily crop evapotranspiration, daily capillary upflow from and daily percolation to a fluctuating water table during a rotation period with wheat growing in a dry season and maize in a rainy season. The water table depth varied in the range 0·7–2·3 m during the maize growth period and 1·6–2·4 m during the wheat growth period. Experimental results showed that the capillary upflow and the percolation were significant components of the soil water balance. Three distinctly different phases for the water fluxes at the water table were observed through the rotation period: water downward period, the period of no or small water fluxes, and water upward period. It implied that the temporal pattern of these water fluxes at the water table was intimately associated with the temporal distribution of rainfall through the rotation period. An empirical equation was determined to estimate the capillary upflow in relation to wheat evapotranspiration and root zone soil water content for local irrigation scheduling. Coupled with the FAO‐Penman–Monteith equation, the equation offers a fast and low cost solution to assess the effect of capillary upflow from a water table on wheat water use. Copyright © 2007 John Wiley & Sons, Ltd.

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.

Estimation of groundwater use by crop production simulated by DSSAT‐wheat and DSSAT‐maize models in the piedmont region of the North China Plain

AbstractSustainable water use is in serious crisis in the piedmont region of the Taihang Mountains in the North China Plain, owing to rapid groundwater drawdown. Estimating the water requirement for agriculture, the biggest user of groundwater, will be helpful in understanding groundwater decline. Through the use of DSSAT‐3·5 wheat and maize models, we assessed water use in winter wheat and maize, two staple crops in the region, in 1987–2001. Trends between groundwater change and simulated agricultural water use were compared. The results showed that groundwater decline was sensitive to simulated crop water requirement and irrigation requirement. According to regression analysis, 100 mm of water requirement by cultivated land (mainly wheat and maize) resulted in about 0·64 m of groundwater decline. This relationship might be useful in understanding the regional water balance and to help decision‐makers control groundwater decline through controlling crop water use or through long‐distance water transfer. The study demonstrated the usefulness of using the DSSAT model for estimating crop water use and the effectiveness of clarifying the reason for groundwater decline using the simulation results of water use. Copyright © 2006 John Wiley & Sons, Ltd.

Nitrogen use and crop type affect the water use of annual crops in south-eastern Australia

The effect of management and crop selection on water use and profile drying was investigated using 2 series of experiments conducted in the Victorian Wimmera. The effect of applied nitrogen on growth and water use of canola was assessed from 3 field experiments on a Vertosol soil. Across these sites, 140 kg N/ha increased crop water use by a mean of 30 mm, and the biological response averaged 3.68 t/ha of shoot dry matter and seed yield increased by 73% from 1.46 to 2.52 t/ha. The additional nitrogen enabled roots to go deeper into the soil and also to extract water to higher tensions, but the increases in water use were far less than the growth and yield responses. Estimated average soil evaporation was 120 mm across these experiments, but ranged from 26 to 57% of total water use. It was concluded that increased crop vigour in response to applied nitrogen does increase total water use, but the main way that water-use efficiency increases is through reduced soil evaporation. In a second series of experiments, the growth, yield, and water use of wheat, canola, linseed, mustard, and safflower were compared across 4 sites with differing soil moisture contents. Wheat was the highest yielding crop at all sites. Mustard and canola produced similar amounts of biomass and seed yields, whereas linseed produced seed yields that were generally less than the brassica oilseeds. Safflower grew well and produced large amounts of biomass at all sites, but this increased growth did not necessarily translate into increased seed yields. Safflower yielded less seed than all other crops at the 2 dry sites, but yields were similar to canola at the wetter sites. On 2 drier sites, soil water extraction occurred to approximately 1 m for all crops, and all available water was used within that zone by all crops. Where the soil was wet beyond 1 m, safflower was able to extract water from deeper in the profile than the other crops and generated a soil water deficit of about 100 mm more than the other crops at maturity. This deficit persisted into the subsequent autumn–winter period. The potential of using safflower as a management option to extract water from deep in the profile, and so create a soil buffer, is discussed.

Subsoil constraints in Vertosols: crop water use, nutrient concentration, and grain yields of bread wheat, durum wheat, barley, chickpea, and canola

Single or multiple factors implicated in subsoil constraints including salinity, sodicity, and phytotoxic concentrations of chloride (Cl) are present in many Vertosols including those occurring in Queensland, Australia. The variable distribution and the complex interactions that exist between these constraints limit the agronomic or management options available to manage the soil with these subsoil constraints. The identification of crops and cultivars adapted to these adverse subsoil conditions and/or able to exploit subsoil water may be an option to maintain productivity of these soils. We evaluated relative performance of 5 winter crop species, in terms of grain yields, nutrient concentration, and ability to extract soil water, grown on soils with various levels and combinations of subsoil constraints in 19 field experiments over 2 years. Subsoil constraints were measured by levels of soil Cl, electrical conductivity of the saturation extract (ECse), and exchangeable sodium percentage (ESP). Increasing levels of subsoil constraints significantly decreased maximum depth of water extraction, grain yield, and plant-available water capacity for all the 5 crops and more so for chickpea and durum wheat than bread wheat, barley, or canola. Increasing soil Cl levels had a greater restricting effect on water availability than did ECse and ESP. We developed empirical relationships between soil Cl, ECse, and ESP and crop lower limit (CLL) for estimating subsoil water extraction by 5 winter crops. However, the presence of gypsum influenced the ability to predict CLL based on the levels of ECse. Stronger relationships between apparent unused plant-available water (CLL – LL15; LL15 is lower limit at –1.5 MPa) and soil Cl concentrations than ESP or ECse suggested that the presence of high Cl in these soils most likely inhibited the subsoil water extraction by the crops. This was supported by increased sodium (Na) and Cl concentration with a corresponding decrease in calcium (Ca) and potassium (K) in young mature leaf of bread wheat, durum wheat, and chickpea with increasing levels of subsoil constraints. Of the 2 ions, Na and Cl, the latter appears to be more damaging than the former, resulting in plant dieback and reduced grain yields.

Wheat yield response to line-source sprinkler irrigation in the arid Southeast Anatolia region of Turkey

In the arid Southeast Anatolia Project (GAP) region of Turkey, crop yields are mainly limited by available water. A field experiment was conducted for wheat ( Triticum durum L.) during the period 1993–1996 to evaluate the effects of deficit irrigation on yield and water use efficiency. Two line-source sprinkler laterals were used in order to create gradually varying deficit irrigation treatments (I 1 through I 5) with the two fixed irrigation intervals of 7-day (IF 1) and 14-day (IF 2). Irrigation water was applied based on cumulative Class-A Pan evaporation for the irrigation interval of 7-day (IF 1I 1); and to replenish soil water deficit in the 90 cm depth to the field capacity for the 14-day irrigation interval in treatment plots adjacent to sprinkler lateral (IF 2I 1). The results revealed that grain yield response to irrigation varied considerably due to differences in soil water contents and winter rainfall distribution in the experimental years. Highest average grain yields were attained from the highest irrigation level (I 1) with 7-day interval in 1994, 1995 and 1996 as 8340, 6720, and 8070 kg/ha, respectively. The corresponding yield values for the 14-day treatment plots were 7720, 7130, and 7600 kg/ha. Yields of the least watered treatment (I 5) varied with seasonal rainfall and its distribution. Grain yields decreased with increasing distance from the line-source in both irrigation intervals. Severe soil water deficits significantly decrease grain yield. The two irrigation intervals for the same water level resulted in similar yields. ET was largest in the treatment plots adjacent to the laterals (I 1). Seasonal water use increased with increasing irrigation levels. Soil water deficit significantly reduced ET, which mainly depends on irrigation amounts. Seasonal water use of wheat in I 1 treatment ranged from 571 to 721 mm in three experimental years. The crop coefficients ( K c) curves were developed for the different treatments using the reference ET and actual monthly ET values during the experimental years. K c values ranged from 0.6 during initial stage to 1.35 at anthesis for the I 1F 1 irrigation treatment. Significant linear relationships ( R 2 = 0.81) between water use and grain yield were obtained in each season. The highest dry matter yield was obtained from I 1 treatment plots in the experimental years. Yield response factor ( k y), which is the slope of relative evapotranspiration deficit and relative yield reduction, for wheat was calculated as 1.01. Consistently higher values of harvest index (HI) were obtained from the I 1 treatment plots. HI decreased with decreasing irrigation water amount. The highest WUE averaging 14.2, 14.9 and 12.6 kg/ha/mm were obtained in IF 1I 2, IF 2I 4, and IF 1I 4 treatments, respectively in 1993/1994, 1994/1995 and 1995/1996 growing seasons. Severe deficit irrigation treatment I 5 in general resulted in minimum WUE in the experimental years.

Water use of wheat, barley, canola, and lucerne in the high rainfall zone of south-western Australia

Water use of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), canola (Brassica napus L.), and lucerne (Medicago sativa L.) was measured on a duplex soil in the high rainfall zone (HRZ) of south-western Australia from 2001 to 2003. Rainfall exceeded evapotranspiration in all years, resulting in transient perched watertables, subsurface waterlogging in 2002 and 2003, and loss of water by deep drainage and lateral flow in all years. There was no significant difference in water use among wheat, barley, and canola. Lucerne used water at a similar rate to annual crops during the winter and spring, but continued to extract 80−100 mm more water than the annual crops over the summer and autumn fallow period. This resulted in about 50 mm less drainage past the root-zone than for annual crops in the second and third years after the establishment of the lucerne. Crop water use was fully met by rainfall from sowing to anthesis and a significant amount of water (120−220 mm) was used during the post-anthesis period, resulting in a ratio of pre- to post-anthesis water use (ETa : ETpa) of 1 : 1 to 2 : 1. These ratios were lower than the indicative value of 2 : 1 for limited water supply for grain filling. High water use during the post-anthesis period was attributed to high available soil water at anthesis, a large rooting depth (≥1.4 m), a high proportion (15%) of roots in the clay subsoil, and regular rainfall during grain filling. The pattern of seasonal water use by crops suggested that high dry matter at anthesis did not prematurely exhaust soil water for grain filling and that it is unlikely to affect dry matter accumulation during grain filling and final grain yield under these conditions.

Long-term effect of cropping system and nitrogen and phosphorus fertilizer on production and nitrogen economy of grain crops in a Brown Chernozem

Assessment of the long-term impact of fertilizers and other management factors on crop production and environmental sustainability of cropping systems in the semi-arid Canadian prairies is needed. This paper discusses the long-term influence of N and P fertilizers on crop production, N uptake and water use of hard red spring wheat (Triticum aestivum L.), and the effect of the preceding crop type [flax (Linum usitatissimum L.) and fall rye (Secale cereale L.)] on wheat grown on a medium-textured, Orthic Brown Chernozem at Swift Current, Saskatchewan. We analysed 36 yr of results (1967–2002) from eight crop rotation-fertility treatments: viz., fallow-wheat receiving N and P (F-W, N + P), three F-W-W treatments fertilized with (i) N + P, (ii) P only, and (iii) N only; two other 3-yr mixed rotations with N + P (i) F-flax-W (F-Flx-W) and (ii) F-fall rye-W (F-Rye-W); and two continuous wheat rotations (Cont W), one receiving N + P and the other only P. Growing season weather conditions during the 36-yr period were near the long-term mean, but the first 22 yr were generally drier than normal while the last 14 yr (1989–2002) had average to above-average growing conditions. This was partly responsible for grain and N yield being greater in the latter period than in the first 22 yr. The 36-yr average response of wheat grown on fallow to P fertilizer was 339 kg ha-1, while the response to N fertilizer over this period was only 123 kg ha-1. The 36-yr average response of wheat grown on stubble to N was 344 kg ha-1 for F-W-(W) and 393 kg ha-1 for Cont W. Neither flax nor fall rye influenced the yield response of the following wheat crops. Annualized grain production for F-W (N + P), F-W-W (+ N) and F-W-W (+ P) rotations were similar (1130 kg ha-1 yr-1); this was about 15% lower than for F-W-W (N + P), 40% lower than for Cont W (N + P), and 5% lower than for Cont W (+ P). Annualized aboveground N yield for Cont W (N + P) was 57% higher than for Cont W (+ P). Regressions were developed relating straw to grain yields for wheat, flax and fall rye. The amount of NO3-N left in the soil was directly related to amount of N applied and inversely to N removed in the crop. Thus, F-(W)-W (+ N) left about 28% more NO3-N in the rooting zone than F-(W)-W (N + P), while F-W-(W) (N + P) left 20% more than F-W-(W) (+ P), and Cont W (N + P) left 39% more than Cont W (+ P). F-Rye-W (N + P) left much less NO3-N in the soil than any other fallow-containing system and similar amounts to Cont W (N + P). Key words: Yields, grain protein, N and P fertilizer, straw/grain regressions, water use, soil nitrate

Interactive effects of elevated atmospheric CO 2 concentrations and plant available soil water content on canopy evapotranspiration and conductance of spring wheat

The present study was conducted to investigate the possible interactive effects of rising atmospheric CO 2 concentration [CO 2] and drought stress on water use of wheat. Spring wheat ( Triticum aestivum cv. “Minaret”) was grown either in 1 m diameter lysimeters with 0.4 m soil depth (1998) or in the field (1999) in open-top chambers under two CO 2-concentrations (ambient, ambient + 280 ppm) and two watering regimes (well-watered = WW with a plant available water content PAW > 40 mm and drought stressed = DS, 10 mm < PAW < 30 mm) beginning after first node stage. Canopy evapotranspiration ( E C) was measured continuously from first the node stage until the beginning of flag leaf senescence using four open-system canopy chambers (0.78 m 3). Seasonal changes of the absorption of photosynthetically active radiation (APAR) of the canopy and root growth (1999) were also measured. In both growing seasons leaf area index increased in response to elevated [CO 2] in both water treatments. The related effects of [CO 2] on canopy radiation absorption (APAR) were, however, smaller. E C was linearily related to APAR in both growing seasons. While elevated [CO 2] reduced the slope of this relation under WW conditions by ca. 20% in both growing seasons, it was not reduced (1998) and even increased (1999) under drought. Canopy conductance ( G C) calculated as E C divided by vapour pressure deficit of air, showed a non-linear relationship to APAR that was best explained by saturation curves. Under WW conditions, elevated [CO 2] reduced the initial slope of G C versus APAR as well as G C at saturating light conditions (ca. −30%), while under DS conditions no effect of elevated [CO 2] could be detected. Under high light conditions (PAR > 400 μmol m −2 s −1) a critical “threshold value” of PAW ( T PAW, ca. 40 mm) could be identified above which G C did not respond to PAW. While in 1998 G C did not respond to elevated [CO 2] at PAW < T PAW, it was slightly increased at low PAW values in the field experiments of 1999. The reduction of T PAW by elevated [CO 2] may be explained by enhanced root growth (1999) that would have given the plants better access to soil water resources. The present results suggest that below a critical soil water content elevated [CO 2] will not reduce canopy water loss of wheat or may even enhance it.

Interactions between elevated CO2 and added N: effects on water use, biomass, and soil 15N uptake in wheat

The interaction between atmospheric CO2 (ambient=365 ppmv, elevated=500 ppmv) and fertilizer N (6, 12 and 18 g N m−2) was examined in spring wheat (Triticum aestivum, L.) grown on a 15N-labelled sandy loam soil. Wheat shoots were pulse-labelled once with 14CO2 to trace the photosynthetically fixed C within the soil/plant system. Fertilizer N increased root length and canopy water use efficiency (WUE). At each N level, root length and WUE were higher under elevated than under ambient CO2, but no CO2-N interaction was observed. The N concentration in roots, but not in shoots, was affected by a CO2-N interaction. Fertilizer N increased and elevated CO2 decreased shoot N concentrations. The root-to-shoot (R/S) ratio decreased with N addition and was affected by interactions between N and CO2. Plant biomass C and N increased significantly with increased N addition. The effect of elevated CO2 on shoots was relatively small regardless of N level, whereas roots experienced a clear CO2-N interaction. The 14C recovered one week after labelling was mainly in the shoot biomass (80%). The activity increased with N addition, reflecting a larger shoot biomass, but the relative distribution of 14C between shoots, roots, soil and rhizosphere respiration was little affected by CO2 level and N addition. Soil 15N contributed 7.1 to 9.0 g N m−2 to shoot N, the total increase (9.3 to 24.3 g N m−2) being dominated by contributions from fertilizer N. We conclude that effects of elevated CO2 on wheat tissue N cannot be compensated for by N additions, and that plant uptake of native soil N is marginally affected by added N and elevated CO2.

Effects of elevated CO2 concentration on growth, water use, yield and grain quality of wheat under two soil water levels

Wheat (Triticum aestivum L.) is one of the most important food sources in the world. The potential impacts of elevated CO2 on wheat yield and grain quality will have profound influences on the supply and nutritional value of wheat products as well as on many industrial sectors. A growth-chamber experiment was designed to estimate how soil moisture influences the potential effects of elevated CO2 concentration ([CO2]) on wheat growth, water use and grain yield. Spring wheat (T. aestivum cv. Ganmai 8139) was grown in pots placed in controlled growth chambers and was subjected to two [CO2] (approximately 350 and 700l/l, respectively) and two soil water levels (80 and 40% of field water capacity (FWC), respectively). High [CO2] increased plant shoot dry weight by 89% under 80% FWC and by 53% under 40% FWC. Grain yield of wheat was markedly increased under elevated [CO2] with greater grain number and harvest index. The ratio of plant shoot dry weight to height was increased by 75% under high [CO2] at high soil moisture, and by 54% at low moisture. Water use efficiency of shoot (WUEs) and grain yield (WUEg) were increased under high [CO2] because the magnitude of the increase in shoot dry weight and grain yield was greater than that of the cumulative consumption of water under high [CO2] conditions. When wheat plants were under high [CO2] conditions and maintained at high moisture, the WUEs and WUEg were increased by 62 and 128%, respectively. Elevated [CO2] resulted in lower concentrations of mineral nutrients (N, P, K and Zn), lysine and crude protein in mature grains. This was probably caused by a dilution effect induced by great increment of carbohydrate in grains. The total quantity of mineral nutrients, lysine and crude protein accumulated in grains per hectare were still increased under high [CO2] due to increase in grain yield. Our results indicate that high [CO 2] is beneficial to plant growth, yield and WUE, while grain quality was lowered under high [CO2] conditions as reflected by the increased crude starch content, and corresponding decreases in mineral nutrients, lysine and crude protein concentrations. The analysis of yield components suggested that the yield increase was mainly attributable to an increase in the number of grains. However, the effects of CO 2 enrichment on plants depend on the availability of soil moisture, and plants may benefit more from CO 2 enrichment when sufficient water is supplied. © 2004 Elsevier B.V. All rights reserved.

Irrigation and fertilizer effects on water use and yield of spring wheat in semi-arid regions

Controlled irrigation and fertilizing strategies under rainwater-harvesting technology in semi-arid areas were discussed. Effects of the amounts of applied water and fertilizer on water use and yield of spring wheat were determined. The experiment included four water treatments during the spring wheat growth period. The four treatments were (total water applied): rich water (RW), 400 mm; moderate water (MW), 300 mm; low water (LW), 100 mm, and natural water (NW), 212 mm. (In the first three situations, rainfall was excluded from irrigation plots while in the fourth only natural rainfall was utilized.) Four nutrition conditions were set up for each water treatment: high fertilizer (HF) 372 kg ha −1, moderate fertilizer (MF) 248 kg ha −1, low fertilizer (LF) 124 kg ha −1 and without fertilizer application (CK). Each water–fertilizer treatment was replicated three times. Both soil water content and water use efficiency (WUE) (in terms of grain yield) increased with increasing applied water. The mean WUE were 6.37, 5.61, 5.08 and 4.40 kg ha −1 mm −1 in RW, MW, NW and LW, respectively. WUE increased increasing applied N and P fertilizer. Compared with LW treatment, MW and RW resulted in stronger seedlings, larger and deeper root system, and higher leaf area index (LAI). For RW, MW and NW, the maximum of root biomass increased 96.4, 56.6 and 21.6%, respectively, compared with that for LW. The value of LAI increased 95.6, 66.9 and 40.9%, respectively. The values of leaf area duration (LAD) in RW, MW and NW were remarkably higher than that in LW. Under RW, MW, NW and LW condition, the mean grain yield for the four fertilizer treatments were 3290, 2347, 1665 and 964 kg ha −1, respectively. The mean grain yield in RW, MW and NW increased 241, 143 and 73%, respectively, compared with that in LW. Yield components analysis indicates that the quality and quantity of spikelets and floscule played critical role in grain formation of spring wheat. Statistical analysis of experiment results indicates that the minimum coefficient of water-consumption (0.110 mm/(kg ha −1)) occurred in RW, and the relevant optimal fertilizer application amount was 377 kg ha −1. In various water–fertilizer treatments, WUE was the highest (8.733 kg ha −1 mm −1) under rich water with high fertilization, while grain yield was consistently the highest (4514 kg ha −1). This indicates that rich water with high fertilizer is the most efficient way in the experiment. These results may offer help to controlled irrigation and fertilization in agricultural water management in semi-arid regions.

Improved subsoil macroporosity following perennial pastures

Biopores left in the soil by perennial and annual pastures and their effects on macroporosity, water infiltration and the water use and productivity of subsequent wheat and canola crops were investigated in a field experiment on a Sodosol in southern New South Wales. Phases of both lucerne (4 years) and phalaris (10 years) improved the macroporosity and water infiltration into the dense B horizon compared with continuous annual crops and pastures. After removal of lucerne and phalaris, the subsoil (&gt; 12 cm depth) contained similar numbers of pores &gt; 2 mm diameter (228 and 190/m2, respectively) compared with a mean of 68/m2 after annual crops. However water infiltration rate after lucerne was greater than after phalaris, apparently because of more numerous pores &gt; 4 mm, rather than a change in total porosity. The subsoil after phalaris on the other hand contained more pores 0.3 mm in diameter and a higher total porosity, possibly because of more roots around this diameter, and a longer period without traffic or cultivation. The number of lucerne biopores in the subsoil remained unchanged (170–180/m2) for at least 2 crops after the lucerne was removed although the average size decreased. The volume of water extracted from the subsoil by crops following lucerne was similar to that following annual crop/pasture for 10 of the 12 crop comparisons made. For 2 of the crops, more subsoil water (22 and 24 mm) was used after lucerne than after annuals, and in 1 season this was associated with higher yield of canola. During the 3-year study there was no winter waterlogging or post-anthesis water stress, so there was little opportunity for yield responses to improved subsoil structure. The results confirm speculation that the unfavourable structure of dense subsoils can be improved by the biological action of perennial pasture roots, although reduced wheel traffic and cultivation during the pasture phases may also play a role. Further studies will be necessary to demonstrate associated yield improvements.

Dry-period irrigation and fertilizer application affect water use and yield of spring wheat in semi-arid regions

Based on a field study on the semi-arid Loess Plateau of China, the strategies of limited irrigation in farmland in dry-period of normal-precipitation years are studied, and the effects on water use and grain yield of spring wheat of dry-period irrigation and fertilizer application when sowing are examined. The study includes four treatments: (1) with 90 mm dry-period irrigation but without fertilizer application (W); (2) with fertilizer application but without dry-period irrigation (F); (3) with 90 mm dry-period irrigation plus fertilizer application (WF); (4) without dry-period irrigation and fertilizer application (CK). The results indicate that dry-period irrigation resulted in larger and deeper root systems and larger leaf area index (LAI) compared with the non-irrigated treatments. The root/shoot ratio (R/S) in the irrigated treatments was significantly higher than in the non-irrigated treatments. The grain yields in F, W and WF are 1509, 2712 and 3291 kg ha −1, respectively, which are 13.7, 104.3 and 147.9% higher than that (1328 kg ha −1) of CK, and at the same time the grain yields in W and WF are also significantly higher than in F. Water use efficiencies (WUE) in terms of grain yield are 5.70 and 6.91 kg ha −1 mm −1 in W and WF, respectively, being 65.7 and 101.1% higher than that (3.44 kg ha −1 mm −1) of CK. The highest WUE and grain yield consistently occurred in WF, suggesting that the combination of dry-period irrigation and fertilizer application has a beneficial effect on improving WUE and grain yield of spring wheat.

Windbreak research in a South Australian cropping system

This paper presents the results of 3 years (1994–96) work on the effect of shelter created by a 9 m high Aleppo pine (Pinus halepensis) windbreak in the Mediterranean environment of South Australia on the productivity of wheat, canola, faba beans and oats. Elements of the classic windbreak signature could be detected in the yield responses of 6 of 8 crop years. For example, in the dry year of 1994, yields in the sheltered zone (3–6 H) were 44, 49 and 81% greater than in the exposed zone (18–24 H) for wheat, faba beans and canola, respectively. In 1995, a wet year, only faba beans showed a response (18% increase). In 1996, oats showed an apparent 25% yield increase in the sheltered zone compared with the unsheltered zone. However, these yield differences were not due to shelter alone. For example, covariate analysis of 1995 wheat and bean yield data with soil texture indicated that yield variation across the paddock could be explained by variation in depth to calcareous clay loam. Cumulative water use of wheat was greater in the 3–12 H zone in 1994 (dry year) but less in 1995 (wet year); however, these differences are likely to be also due to soil variation in the 2 plots used. Nevertheless, the windbreak effectively altered the microclimate. Cumulative temperature was measured at 4 distances on the leeward side of the windbreak and used to predict the time taken for wheat to reach anthesis at each location. The correlation between normalised values of observed and predicted times to anthesis was found for 3 wheat crops with different times of sowing in 1995 (r2 = 0.62). It was concluded that (i) shelter will affect the physiology of crops grown in this environment, (ii)�the shelter effect on enhancing crop yield is relatively subtle compared with other sources of yield variation and (iii)�the evidence for a water-saving mechanism in enhancing crop yield is inconclusive.

Crop growth, yield and water use in long fallow and continuous cropping sequences in the Victorian mallee

The agronomic implications of substituting mustard (Brassica juncea) for long (winter) fallows were investigated in a 6-year field experiment by comparing 2 cropping sequences (fallow–wheat–pea v. mustard–wheat–pea) in the semi-arid Victorian mallee. Production and water use of wheat, pea and mustard were measured. Grain yields ranged from 0.1 to 2.4 t/ha for wheat (mean 1.72 t/ha after fallow and 1.22 t/ha after mustard); from 0 to 0.6 t/ha (mean 0.22 t/ha) for mustard and from 0 to 1.4 t/ha (mean 0.8 t/ha) for field pea, strongly reflecting variable seasonal conditions (in-crop rainfall range from 84 to 231 mm). Mustard was shown to be a potential replacement for long fallow producing additional yield benefit (mustard + wheat) in one year. However, under drought conditions it introduces severe penalties to wheat growth and yield compared with the traditional fallow cropping system. Further, mustard did not affect water use, growth, or yield of the second crop after wheat (in our case field pea). This study highlights a conflict between developing farming systems that are productive, environmentally and socially acceptable under variable weather conditions and yet uphold the regional need to reduce dependence on fallowing. Further analyses of weather patterns and other crop choice strategies are needed to help develop better management strategies for the mallee region of Australia.

Effect of shelter on the yield and water use of wheat

Wheat was grown in the field and lysimeters under 3 experimental regimes — full exposure to wind, full shelter within an enclosure, and partial shelter behind an artificial windbreak — to test the hypothesis that a crop in a sheltered environment will be more conservative in its water use and more efficient in using that water to grow biomass. The fully sheltered wheat crop in the field produced 11% more above-ground biomass than the exposed crop and most of this difference was attributed to leaf (20%) and stem (21%) material. However, the sheltered crop had lower 1000-grain weights (35.6 g cf. 40.1 g) and higher protein (14.3% cf. 11.5%). No significant difference between sheltered and exposed yields could be confidently detected.Plants grown under non-water limiting conditions of lysimeters produced 14% more biomass under shelter and were also likely to be more efficient (7%, P = 0.06) in their use of water to produce that biomass than wind-exposed plants. Shelter did not change the total soil water use of the lysimeter- or field-grown wheat. However, the sheltered field crop was more conservative than the exposed crop in its use of soil water up to anthesis and less conservative during grain filling. In the partial shelter regime wheat was grown in the ground and in lysimeters at distances of 3�H (i.e. 3 × windbreak height), 6 H, 12 H, 15 H, 18 H and 24 H from an artificial windbreak. Significant relationships with distance from this windbreak were only observed in total biomass, stem weight and head weight of field-grown wheat at anthesis. In summary, the sheltered wheat was more efficient in production of biomass and did conserve water early in the growing season but the conserved soil water was expended to maintain that biomass at the expense of grain size.

Effect of irrigation and nitrogen level on yield, nutrient uptake and water use of late sown wheat (Triticum aestivum)

A field experiment was conducted during the winter (rabo seasons of 1996 97 to 1998 99 at Bilaspur, Chhattisgarh, to study the yield, water use and nutrient uptake of wheat (Trticum aestivum L. emend. Fiori Paol.) as affected by varieties, irrigation and nitrogen level under late sown conditions. Among the varieties, DL 788 2 and DL 803 3 were superior to GW 190 and GW 173 . Irrigation applied at 1.2 IW : CPE ratio gave significantb higher grain yield than 0.6 and 0.9 ratios. Application of 120 kg Nlha gave higher yield and yield attributes than 80 kg Nlha. Total nutrient uptake was positively influenced by irrigation and N levels. Total water use was lowest (29.60 cm), while water use efficiency was highest with 0.6 IW : CPE.The WUE decreased with the increase in fre quency of irrigation. The moisture depletion from upper soil layers (0 60 cm) was higher than lower layers (60 90 cm). However, total profile moisture contribution was highest with limited water supply (0.6 IW : CPE) and de creased with the increase in number of irrigation. Canopy temperature was comparatively low than ambient tem perature under higher moisture (1.2 or 0.911.2 IW : CPE) than lower moisture regime (0.6 IW : CPE).