Low Rainfall Years Research Articles

Leptospirosis in a subsistence farming community in Brazil

Leptospirosis has been reported in rural areas of Brazil. However, there is limited information about the exposure risk or the risk of Leptospira infection for rural-based populations. A cross-sectional study was carried out in order to determine the prevalence and risk factors for prior Leptospira infection in a rural subsistence farming region of the state of Rio Grande do Norte, an area in which outbreaks of leptospirosis have occurred. Among 290 individuals enrolled, 44 (15.2%) had anti-Leptospira IgM antibodies as determined by IgM ELISA. Infection tended to occur with activities related to the rice fields (P=0.08). Our findings indicate that Leptospira infection occurs even in years of low rainfall, and may have an important impact among poor rural-based subsistence farmers in Brazil. Additional studies are needed to characterize the mode of transmission in this region.

Harvest Techniques Change Annual Warm‐Season Legume Forage Yield and Nutritive Value

Comparison among warm‐season legume forage trials may not be valid if harvest techniques vary. To address this question, herbage dry matter (DM) yields, branching, crude protein (CP), and fiber concentrations for nine warm‐season annual herbaceous legumes were measured by hand‐plucking all leaves and pliable tips or clipping at 7.5‐ or 15‐cm height. The experiment was conducted in Texas on a Windthorst fine sandy loam over 2 yr. Harvest technique did not affect DM yield in 2004, but the hand‐plucked harvest technique produced 34 to 39% less forage in 2005 (low rainfall year) compared with the clipped plots. Most entries had greater branching on hand‐plucked than on clipped plants (entry by harvest P < 0.05). Crude protein concentration was greater (P < 0.05) and fiber concentrations lower in the hand‐plucked compared with the clipped plants. These results suggest that neither yields nor nutritive values of hand‐plucked forage trials examining annual warm‐season herbaceous legumes should be compared with clipped forage trials, whereas clipping heights may be less problematic. Results support a careful choice of experiment harvest technique based on the future field‐scale harvest method or degree of target herbivore selectivity.

Supplemental irrigation of wheat with saline water

In arid and semi-arid regions, both rainfall and surface irrigation water supplies are unreliable and inadequate to meet crop water requirement. Groundwater in these regions is mainly marginally saline (2–6 dS/m) to saline (>6 dS/m) and could be exploited to meet crop water requirement if no adverse effects on crops and land resource occur. The fear of adverse effects has often restricted the exploitation of naturally occurring saline water. The results reveal that substituting a part or all except pre-sowing irrigation with saline water having an electrical conductivity (EC iw) of 8 dS/m is possible for cultivation of wheat. Similarly, saline water with EC iw ranging between 8 and 12 dS/m could be used to supplement at least two irrigations to obtain 90% or more of the optimum yield. In low rainfall years, the use of such waters for all irrigations, except pre-sowing, produced more yield than skipping irrigations. Apparently, even at this level of osmotic salt stress, matric stress is more harmful. Thus, it would be interesting to use such waters for wheat production in monsoon climatic regions.

Effects of Greater flamingo Phoenicopterus ruber on macrophytes, chironomids and turbidity in natural marshes in Donana, SW Spain

Top predators and nutrient inputs are important factors determining the structure of freshwater aquatic systems. Greater flamingos (Phoenicopterus ruber) have been shown to destroy submerged macrophytes and may promote a switch from clear water to turbid water in the temporary marshes of Donana National Park. We excluded flamingos from twenty 4x4 m plots distributed between two lucios (shallow seasonal lakes) within the marshes from February to July 2004. In July, we measured total suspended solids (TSS), macrophyte biomass and abundance and size of chironomid larvae in the twenty exclosures and twenty adjacent control plots. TSS was lower and macrophyte biomass was higher in exclosures, but not significantly so. Flamingos were found to cause a significant reduction in chironomid abundance and an increase in the proportion of larger larvae. The effect of exclusion was greater where the density of flamingos was highest. Comparison with the results of previous studies suggests that the impact of flamingos is context dependent and largely determined by bird density and/or factors related to macrophyte productivity. Water levels were especially high in 2004 owing to heavy rains, and flamingos may have stronger effects in years of lower rainfall.

A review of recent climate variability and climate change in southeastern Australia

AbstractSoutheastern Australia (SEA) has suffered from 10 years of low rainfall from 1997 to 2006. A protracted dry spell of this severity has been recorded once before during the 20th century, but current drought conditions are exacerbated by increasing temperatures. Impacts of this dry decade are wide‐ranging, so a major research effort is being directed to better understand the region's recent climate, its variability and climate change. This review summarizes the conditions of these 10 years and the main mechanisms that affect the climate.Most of the rainfall decline (61%) has occurred in autumn (March–May). Daily maximum temperatures are rising, as are minimum temperatures, except for cooler nights in autumn in the southwest of SEA closely related to lower rainfall. A similar rainfall decline occurred in the southwest of western Australia around 1970 that has many common features with the SEA decline. SEA rainfall is produced by mid‐latitude storms and fronts, interactions with the tropics through continental‐scale cloudbands and cut‐off lows.El Niño‐Southern Oscillation impacts on SEA rainfall, as does the Indian Ocean, but neither has a direct influence in autumn. Trends have been found in both hemispheric (the southern annular mode) and local (sub‐tropical ridge) circulation features that may have played a role in reducing the number and impact of mid‐latitude systems around SEA, and thus reducing rainfall. The role of many of these mechanisms needs to be clarified, but there is likely to be an influence of enhanced greenhouse gas concentrations on SEA climate, at least on temperature. Copyright © 2007 Royal Meteorological Society

LONG-TERM YIELD SUSTAINABILITY AND FINANCIAL RETURNS FROM GRAIN LEGUME–MAIZE INTERCROPS ON A SANDY SOIL IN SUBHUMID NORTH CENTRAL ZIMBABWE

To measure the yield and financial returns from five grain legume–maize intercrop combinations over 12 years of cropping, a field experiment was conducted on a loamy sand soil in the subhumid unimodal rainfall environment of Domboshava in north-central Zimbabwe. Inputs and management followed smallholder practice, including partial grazing of crop residues and a zero mineral fertilizer treatment. The intercropped legumes grew moderately well most years. Cowpea averaged the highest grain yield (0.244 t ha−1) and haulm yield (1.54 t ha−1) over the 12 years, followed by pigeonpea and sugar bean. Intercropped pigeonpea yield was the least variable of the legumes over the years. Maize grain yield was highly variable across years with or without fertilizer and was reduced in years of low (533 mm) and high (1313 mm) rainfall. The pigeonpea–maize intercrop grown without fertilizer produced 0.11 t ha−1 (6.25 %) more maize grain yield per year than sole crop maize, in addition to pigeonpea grain and haulms. Intercropped cowpea (which yielded more than double the above-ground non-grain biomass of pigeonpea) had less effect on maize grain yield. There was no trend to greater benefits from the legumes on maize yield after more years of intercropping. Net present values of annual margins accumulated over the 12 years for sole maize with fertilizer (US$1719 ha−1) and without fertilizer (US$935 ha−1) were higher than the fertilized and unfertilized intercropping options (US$1017 and US$745 ha−1). Pigeonpea or cowpea–unfertilized maize generated more financial returns than the other intercrops, but the low yields and high labour costs for the legumes made the intercrops financially unattractive. We conclude that regularly intercropped pigeonpea or cowpea can to a small extent help to maintain maize yield when maize is grown without mineral fertilizer on sandy soils in sub humid zones of Zimbabwe, and simultaneously provide some nutritious food, but that financial considerations will encourage smallholder farmers to persist with growing low input sole crop maize.

Tree and Crop Growth and Soil Resource Availability in Hardwickia binata Roxb Agroforestry Systems in the Indian Desert

Integrating trees in agricultural fields may be beneficial in controlling land degradation and improving productivity in dryland areas. Two-year-old Hardwickia binata Roxb trees were intercropped for 7 years to examine tree-crop interactions and the effect of tree integration and the cropping pattern on land productivity. The tree integrated treatments comprised a Vigna radiata (L.) R. Wilcz crop with H. binata in all years (fixed crop) (FC) and a rotation crop with H. binata in alternate years (RC). Sole crop treatments provided controls for the V. radiata crop (CFC) and rotational crop (CRC) treatments. Pennisetum glaucum (L.) R.Br., V. radiata, Sesamum indicum (L.) and Cymopsis tetragonoloba (L.) Taub were harvested in the RC/CRC plots in 1996, 1997, 1998, 1999, 2000, 2001, and 2003. Tree growth and growth increments did not differ between the FC and RC treatments (p > 0.05). Crop yield (grain + dry matter) was highest (p < 0.01) in the FC treatment in 1996, 1997, 1998, 1999, and 2000, indicating that the presence of trees was beneficial. The observation that yield was highest in the CFC/CRC treatments in 2001 and 2003 indicates a competitive effect of trees for soil resources in these years. Soil water content (SWC) in September was lowest in 2002 and highest in 2003. The effect of cropping pattern on SWC was significant (p < 0.05) only in 2000, 2001, 2002, and 2003, whereas SWC differed (p < 0.01) between 0–25-, 25–50-, and 50–75-cm soil layers. Soil water content to 75-cm soil layer was lower by 0.4 (1996) to 18.9 mm (2003) in tree-integrated treatments than in the control treatments, affecting crop yield. Soil organic matter, NH4-N, NO3-N, and PO4-P in the 0–25-cm soil layer were increased by tree inputs (p < 0.05). H. binata was apparently beneficial in increasing productivity even during droughts, and the benefits may be further improved by root trenching to reduce competition for soil resources in relatively low rainfall years.

Toward the development of prediction models for the primary Caribbean dry season

Two statistical models are created for the Caribbean during its dry season. Canonical correlation analysis (CCA) confirms that there is a robust El Nino Southern Oscillation (ENSO) signal in the region during the dry season and that the mode manifests itself as oppositely signed precipitation anomalies over the north and south Caribbean. The south-eastern Caribbean becomes dry in response to a warm event. The first statistical model consequently uses a rainfall index averaged over the south-eastern Caribbean as the predictand. A model which retains an ENSO proxy as one of two predictors shows reasonable skill with hindcast predictions for the region. A second model is created using a Jamaican rainfall index as predictand. Jamaica falls in the transition zone i.e. between the oppositely signed north-south precipitation anomalies characteristic of the ENSO dry season mode. In this case no ENSO related predictor is retained in the final model. Composite analysis of select atmospheric variables for anomalously high and low rainfall years (for the dry season) give an understanding of the dynamics of the Caribbean dry season during phases of the ENSO, particularly those which lead to the creation of the transition zone.

Savanna herbivore dynamics in a livestock-dominated landscape. II: Ecological, conservation, and management implications of predator restoration

Conserving African wildlife in human-occupied landscapes requires management intervention that is guided by a mechanistic understanding of how anthropogenic factors influence large-scale ecological processes. In Laikipia District, a dry savanna region in northern Kenya where wildlife share the landscape with humans and livestock, we examined why five of nine wild ungulate species suffered protracted declines on properties receiving the greatest conservation investment. Of 10 alternative causes examined, only an increase in predation, interacting with brief periods of high and low rainfall, was consistent with the timing, synchrony, duration and species composition of observed ungulate declines. The principal factor causing predation to increase was a shift in land use from cattle ranching, under which predators and plains zebras were severely suppressed, to wildlife conservation and ecotourism. This prompted a 5-fold increase in plains zebra abundance, and created a demand for living predators. Plains zebras ultimately comprised more than half the available prey biomass, and supported a substantial predator community, but were not limited by predators. We infer that increasing predation pressure caused predator-susceptible prey species to decline, via mechanisms that included apparent competition. Herbivore dynamics in Laikipia shared features with previously reported responses by prey communities to predator manipulation in Kruger and Serengeti National Parks. All featured one or a few numerically dominant herbivore species, which were primarily limited by rainfall and density, supporting a predator community that in turn limited the abundance of other prey species. In each case, predation had a profound effect, but on only a subset of prey species, reducing the evenness component of prey diversity. The presence of cattle in the landscape may affect predator–prey dynamics in both direct and indirect ways, depending on rainfall. In extreme years (floods or drought), episodic die-offs temporarily subsidize scavenging predators. In low rainfall years, competition between plains zebras and cattle, which negligibly support predators, may indirectly limit predator carrying capacity. Consequently, removal of cattle may favor not only zebras, but also their predators, and further depress predator-susceptible prey species.

Paired catchments observations on the water yield of mature eucalypt and immature radiata pine plantations in Victoria, Australia

Results from a paired catchment project measuring the water balance of native eucalypt forest and the change caused by conversion of one catchment to radiata pine are presented. The results are from 1975 to 1987 and from 1997 to 2006. The project measured the water yield from three small, steep, contiguous, forested catchments carrying similar native eucalypt vegetation in south-eastern Australia. One of the catchments was converted to radiata pine in 1980. Data from the untreated catchment showed that annual water yield was substantially a function of annual rainfall, and that annual rainfalls below 900 mm generated little runoff. The conversion to radiata pine led to an increased water yield of up to 300 mm per annum immediately after clearing. This response has declined but in general the runoff from the pine catchment is still higher than that of the eucalypt catchment except for “drought” years. Combination of these results with other Australian results gave a simple model of radiata pine water use (relative to the native eucalypt vegetation) as a function of age and annual rainfall. Older trees and low-rainfall years are associated with a higher water use by the radiata pine than the native forest, but conversely younger trees and higher rainfalls give lower water use. Extrapolation of the results to grassland showed that reforestation of grassland sites would lead to diminished yields. The relationships generated may be useful for estimation of the net change in streamflow caused by afforestation with radiata pine in larger catchments.

Effects of 15 years of conservation tillage on soil structure and productivity of wheat cultivation in northern China

An understanding of long-term tillage and straw management impact on soil structure and productivity is necessary for the further development of conservation tillage practice in dryland farming areas. Data from a 15-year field experiment conducted in Shanxi, on the loess plateau of northern China, were used to compare the long-term effects of no-till and residue cover (NTSC) with conventional tillage (CT) in a winter wheat (Triticum aestivum L.) monoculture. Long-term CT and straw removal resulted in poor soil structure and low productivity. Mean soil bulk density in NTSC was 1.5% less than in CT and capillary porosity (&lt;60 μm) 3.2% greater. Water stability of macro-aggregates &gt;2 mm was much greater for NTSC in the 0–0.20 m profile. Soil organic matter and total N and P were 27.9%, 25.6%, and 4.4% greater in NTSC, respectively, and earthworms (19/m2) were found only in the no tillage treatment. Crop yield and water use efficiency tended to be higher under NTSC than under CT, especially in the years of low rainfall, suggesting that the change in soil structure has provided a better environment for crop development. Our 15-year experimental data indicate that NTSC is a more sustainable farming system, which can improve soil structure, and increase productivity with positive environmental impacts in the rainfed dryland farming areas of northern China.

Interactive Effects of Ungulate Herbivores, Soil Fertility, and Variable Rainfall on Ecosystem Processes in a Semi-arid Savanna

Large herbivores can both positively and negatively affect primary productivity and rates of nutrient cycling in different ecosystems. Positive effects of grazers in grasslands have been attributed to migratory behavior of the dominant ungulate species and soil fertility. We studied the effects of grazers on aboveground net primary productivity (ANPP) and N cycling on central Kenyan rangeland characterized by intense, chronic grazing by a mixed community of cattle and resident native ungulates. Exclosure studies conducted at high and low levels of soil fertility showed that both soil fertility and annual rainfall patterns mediate the effects of grazers on ANPP and N cycling. In a low-rainfall year with short (1 month) growing seasons, grazers reduced aboveground productivity regardless of soil nutrient availability. However, in a high-rainfall year with a 5-month growing season, grazers increased ANPP on nutrient-rich glades and suppressed ANPP on nutrient-poor bushland sites. Concomitant studies of grazer effects on N cycling revealed complex interactions with the seasonal pattern of N-mineralization and inorganic N availability. Grazers increased the size of the inorganic N pool available to plants at the onset of the growing season, particularly in nutrient-rich glades. However, grazers also decreased N mineralization rates at all sites early in the growing season. Measures of N availability via ion-exchange resin bags suggested that the combined effects of grazers on inorganic N pool fluctuations and N-mineralization rates resulted in a net increase in N availability at glade sites and a net decrease in N availability at bushland sites. The net effect of grazers on soil N availability mirrored grazer effects on ANPP in the high-rainfall year. Overall, our results suggest that grazer effects on N dynamics are closely linked to effects on productivity and resilience to drought. Furthermore, even under optimal conditions of high soil fertility and above-average rainfall, grazer promotion of ANPP in this chronically grazed system dominated by resident ungulates was small compared to systems dominated by migratory ungulates.

Influence of density on the seasonal utilization of broad grassland types by white rhinoceroses

We monitored seasonal use of grassland types by white rhinos at two sites within the HluhluweiMfolozi Park (HiP). Thirty-two rhinos were removed from one site to reduce rhino density. Seasonal use of grassland types was similar at both sites, but differed to what a previous study reported. This was likely due to higher food availability during our study, coupled with lower white rhino density. These findings suggest that during high rainfall years, white rhinos at a density of 3/km2 will not overutilize food in the park. Dispersal, initiated by declining food resources, is used to manage white rhino population size in HiP. We suggest that during high rainfall years it is unlikely that dispersal rates will increase. The impact that a similar density would have on food availability and dispersal during low rainfall years is uncertain.

Influence of density on the seasonal utilization of broad grassland types by white rhinoceroses

ABSTRACT We monitored seasonal use of grassland types by white rhinos at two sites within the Hluhluwe-iMfolozi Park (HiP). Thirty-two rhinos were removed from one site to reduce rhino density. Seasonal use of grassland types was similar at both sites, but differed to what a previous study reported. This was likely due to higher food availability during our study, coupled with lower white rhino density. These findings suggest that during high rainfall years, white rhinos at a density of 3/km2 will not overutilize food in the park. Dispersal, initiated by declining food resources, is used to manage white rhino population size in HiP. We suggest that during high rainfall years it is unlikely that dispersal rates will increase. The impact that a similar density would have on food availability and dispersal during low rainfall years is uncertain.

Water policy reform in Australia: lessons from the Victorian seasonal water market*

The nature of the seasonal water market is examined using a theoretical model and empirical evidence from the Victorian market. Drivers of the seasonal opportunity cost of water include the underlying nature of investment in the industry made in the context of risky entitlement yields; and the timing and nature of information regarding seasonal water availability and rainfall. Seasonal water markets facilitate the re‐allocation of water availability according to this short‐run opportunity cost. Evidence from the market suggests that transactions costs are low and most of the existing constraints to trade in seasonal allocations are the result of hydrological conditions. Analysis of market data suggests that the price response of the market to water availability is much more pronounced in years of low rainfall. The implications of the paper for wider policy reform are that attention should be paid to improving property rights for the management of intertemporal risk before other reforms, such as broadening of permanent water markets and institutionalising environmental flows, are implemented. This is because these other reforms will change the spatial and temporal pattern of water use and thus affect reliability, which underpins the value of water in irrigated agriculture.

The Effect of Rainfall on the Abundance of Tarnished Plant Bug Nymphs [Lygus lineolaris (Palisot)] in Alfalfa Fields

Rainfall has generally been overlooked as a regulator of insect population size, especially for mirids (Hemiptera). During a 13-year field study in northwestern New Jersey, total May-June rainfall ranged from 6.5 to 10.7 inches (165–272mm). The highest rainfall reduced first generation nymphs of the tarnished plant bug, Lygus lineolaris (Palisot) (Miridae), in alfalfa by 50%. This reduction was likely mechanical (raindrops knocking the mirids off the plants) rather than biotic, because infections by nematodes and a fungus disease were not significantly increased. The rainfall-reduced mirid populations also had less mortality by the introduced parasite Peristenus digoneutis Loan (Braconidae), probably a result of the lower host density (density dependence). Conversely, in low-rainfall years there were more tarnished plant bugs, and parasitism rates were doubled, so the two mortality factors were complimentary. Rainfall may also be responsible for differences in lygus numbers between regions. Lygus bugs were five times more abundant in Idaho alfalfa than in New Jersey alfalfa, despite considerably higher parasitism rates in Idaho. Perhaps the lower lygus numbers in New Jersey were caused by the nearly four times higher rainfall there.

Variations in the Summertime Atmospheric Hydrologic Cycle Associated with Seasonal Precipitation Anomalies over the Southwestern United States

Abstract This paper examines year-to-year variations in the large-scale summertime hydrologic cycle over the southwestern United States using a suite of regional model simulations and surface- and upper-air-based observations. In agreement with previous results, it is found that observed interannual precipitation variations in this region can be subdivided into two spatiotemporal regimes—one associated with rainfall variability over the southwestern portion of the domain centered on Arizona and the other associated with variations over the southeastern portion centered on western Texas and eastern New Mexico. Because of the limited duration of the model simulation data, it is possible to only investigate one positive rainfall season over the Arizona region and one negative rainfall season over the New Mexico region. From these investigations it appears that for the positive rainfall anomalies over Arizona excess seasonal precipitation is balanced by both enhanced evaporation and vertically integrated large-scale moisture flux convergence. Vertical profiles of these terms indicate that the anomalous large-scale moisture flux convergence is actually related to a decrease in the mean large-scale moisture flux divergence aloft; below 800 mb there is a decrease in the mean moisture flux convergence typically found at these levels, which in turn produces anomalous moisture divergence from the region. For the negative rainfall anomalies over New Mexico similar results, but of opposite sign, are found; one exception is that at the lowest levels there is an additional (negative) contribution to the vertically integrated moisture flux convergence anomaly related to a weakening of the mean low-level moisture flux convergence during the low-rainfall year. Further studies using two different model simulations with the same large-scale dynamic forcing but differing initial soil moisture values indicate that similar balances are also found for rainfall anomalies related to surface soil moisture changes within the domain, suggesting that the changes in large-scale moisture flux convergence described above can be attributed to both year-to-year variations in the regional land–atmosphere interactions as well as variations in the large-scale circulation patterns.

Conditional value-at-risk for water management in Lake Burley Griffin

As the centrepiece of Canberra, Lake Burley Griffin provides the setting for buildings of national importance and a venue for aquatic recreation while, as part of the Molonglo River, the lake has a role in the ecological processes of its broader setting. For the purposes of recreation and landscape a constant water level is preferred: the management plan requires the lake to be maintained at a prescribed normal level. In years of low rainfall this requirement could conflict with the water demands of other users. Episodes of high rainfall may also require compromise between competing objectives. For example, drawdown of lake levels for flood mitigation could impact on the lake's recreational and amenity values and the spill may not be a good use of water. Conditional Value at Risk, a risk measure developed by the financial industry for portfolio management, is defined as the expected loss given that some loss threshold is exceeded. Here, Conditional Value at Risk is applied as decision support for strategic planning and day-to-day operational problems in the hydraulic management of Lake Burley Griffin.

Determining the Causes of Spatial and Temporal Variability of Wheat Yields at Sub-field Scale Using a New Method of Upscaling a Crop Model

Wheat yields in the Mediterranean climate of Western and Southern Australia are often limited by water. Our measurements on a 70 ha growers field showed linear relationships between grain yield and the plant available soil water storage capacity (PAWc) of the top 100 cm of the soil profile. PAWc was linearly related to apparent soil electrical conductivity measured by proximal sensing using electromagnetic induction (EM38). The APSIM wheat model also employs PAWc as one of the systems parameters and simulated linear relationships between PAWc and yield. These relationships were used to transform an EM38-derived PAWc map of the field into yield maps for three major season types (dry, medium and wet) and nitrogen (N) fertiliser management scenarios. The results indicated that the main cause of temporal and spatial yield variability within the field was due to interactions of seasonal rainfall, PAWc and N fertiliser applications. Spatial variability was low in low rainfall years when yields across the field were low and the higher soil water storage capacity sites were often underutilised. With adequate N, spatial variability increased with seasonal rainfall as sites with higher PAWc conserved more water in wet seasons to give higher yield response than sites with low PAWc. The higher yield response of high PAWc sites to rainfall gave rise to larger temporal variability compared with sites with low PAWc. Provision of adequate N is required for the water limited yield potential to be expressed and this increased both spatial and temporal variability. Sites with low PAWc performed poorly irrespective of rainfall and N application. PAWc is inherently low on deep coarse sands; these sites should be considered for a change in land use. Elsewhere, strategic management interventions should aim to improve PAWc through sub-soil amelioration and deep root growth to increase the capital asset of the farm. The resulting increase in yields will occur in favourable seasons and with adequate fertiliser provisions. The largest grain yield response to water and N will be obtained on sites with the highest PAWc and it is at those sites that the greatest profits from fertiliser use could be achieved in wet seasons.

Phosphorus Application Affects the Soybean Root Response to Water Deficit at the Initial Flowering and Full Pod Stages

Application of phosphorus (P) fertilizer is an important factor for improving the tolerance to water deficit in many plants. A pot experiment was conducted to identify the effects of P application on soybean adaptability to water deficit at the R1 (initial flowering) and R4 (full pod) stages through the investigation of root morphological traits, plant P uptake and resultant yield in two soybean (Glycine max L. Merrill) cultivars (Dongnong 46 and Heisheng 101). The four levels of P application were 0, 7.3, 14.6 and 29.2 mg kg−2, respectively. The three water treatments were (1) 65–75% of field water capacity (FWC) as a well-watered control, (2) 30–40% of FWC at the R1 stage, and (3) 30–40% of FWC at the R4 stage. Root traits, plant uptake of P and yield were significantly reduced by water deficiency at different growth stages, especially at the R4 stage. Application of P enabled to alleviate the adverse effects of water deficit, to increase the root dry weight, root length and root surface area, and to slow root senescence after the R5 (initial pod filling) stage. The response of soybean genotypes to both water and P deficit was different. In the absence of P application, Dongnong 46 showed relatively low adaptability to water deficit at the R4 stage, whereas Heisheng 101 showed a lower reduction of root traits and yield. The beneficial effects of P application for Dongnong 46 were more pronounced than those for Heisheng 101. Based on this experiment, we suggested that P fertilizer application to soybean may be justified in low-rainfall years because of its ability to enhance the soybean adaptability to water deficit stress by improving the root morphology, P uptake and consequently yield.