Potential Soil Moisture Deficit Research Articles

Assessment of projected climate change impact on agro‐climatic indicators in Poland

AbstractThis study presents a long‐term assessment of the impact of projected climate change on selected agro‐climatic indicators in Poland. The analysis was based on an ensemble of six bias‐corrected EURO‐CORDEX projections covering the period from 2006 to 2100 under Representative Concentration Pathways: RCP4.5 and 8.5, and partly on simulations of an agro‐hydrological Soil and Water Assessment Tool model. The indicators included growing season (length, beginning, and ending date), growing degree days, frost days, accumulated frost, and planting and harvest timing. The study focused on four major crops cultivated in Poland, namely spring barley, rapeseed, maize silage, and potato. The analysis revealed a significant future increase in precipitation and mean temperature in Poland reaching +10.3% and 3.4°C by the end of century, respectively. Warmer conditions will significantly accelerate the beginning of the growing season (by up to 24 days) and delay its ending (by up to 18 days), consequently significantly extending its length throughout the country (by up to 42 days). A decrease is projected in potential soil moisture deficit by up to 26 mm by the end of century in the high‐end emission scenario. A significant advancement (by up to 30 days) in planting timing is projected for the future for all crops under consideration. A significant increase in growing degree days (by up to 760°C‐days) will also advance the harvest timing (by up to 54 days). The projected temperature increase over the winter season will result in a significant decrease in frost days (by 56 days) and accumulated frost (by 375°C‐days), which may lead to an increased presence of pests. This study can provide a scientific basis for assessing the future risks to the local agriculture from climate change and will be beneficial in planning adaption and mitigation actions for food security at the national and local scale.

Evaluating Optimum Limited Irrigation and Integrated Nutrient Management Strategies for Wheat Growth, Yield and Quality

Agricultural productivity is significantly influenced by the restricted availability of irrigation water and poor soil health. To assess the influence of different potential soil moisture deficit (PSMD) regimes and integrated nutrient levels on the growth, yield, and quality of wheat, an experiment was carried out at the research area of the University of Agriculture, Faisalabad. The experiment includes three levels of PSMD (I1: 25 mm PSMD, I2: 50 mm PSMD, and I3: 75 mm PSMD) and four integrated nutrition levels (N1: 50% organic manure + 50% Inorganic NPK, N2: 75% organic manure + 25% inorganic NPK, N3: 100% application of organic manure, and N4: 100% application of inorganic NPK). Results of the experiment revealed that maximum grain yield (4.78 t ha−1) was obtained as a result of irrigation at 50 mm PSMD with the combined use of organic and inorganic sources in equal proportions. In contrast, the minimum yield was observed at I3: 75 mm PSMD with 100% application of organic manure. The highest plant height (99.11 cm), fertile tillers (284.4), 1000-grain weight (44.48 g), biological yield (14.82 t ha−1), radiation use efficiency for grain yield (RUEGY) (5.71 g MJ−1), and radiation use efficiency for total dry matter (RUETDM) (2.15 g MJ−1) were observed under N1: 50% organic manure with 50% inorganic NPK treatment. The highest value of these parameters was also observed in I2 (50 mm PSMD). The results of this study can be extended to arid and semi-arid regions, where deficit irrigation is a key strategy to address water crises and to meet sustainable development goals.

An enhanced version of the D-Risk decision support webtool for multi-scale management of water abstraction and drought risks in irrigated agriculture

Due to it having the lowest priority for water allocation during drought events and the consequent agronomic and economic impacts of abstraction restrictions, UK irrigated agriculture has been identified as a key business sector ‘at risk’. An enhanced version of the D-Risk webtool has been developed to help agricultural stakeholders and catchment water managers to evaluate the joint multi-scale risks of abstraction restrictions (voluntary and mandatory) and having insufficient irrigation volumes during drought events. The webtool uses annual maximum potential soil moisture deficit as the agroclimate index to calculate monthly and annual volumetric irrigation demand for the selected crop mix, soil available water capacity and location. Simulated river flows are used to identify days not under abstraction restrictions. Annual probability distributions of irrigation deficit and licence utilisation (headroom) are derived from a monthly time-step water balance model that calculates whether the farm irrigation demand in each month can be met, taking account of river flow-based abstraction restrictions, daily and annual volumetric licensed abstraction limits, the licenced abstraction period(s) and any on-farm reservoir storage. The enhanced D-Risk tool provides a more holistic understanding of drought risk on irrigated agriculture from individual farm to catchment scales and supports improved collaborative decision-making regarding future water sharing, water trading and on-farm reservoir investment to reduce business vulnerability to drought and regulatory change.

Performances of climatic indicators from seasonal forecasts for ecosystem management: The case of Central Europe and the Mediterranean

Climate change is affecting the interannual variability and the seasonal cycle for key meteorological variables, as well as the frequency, intensity, duration and timing of out-of-the-norm and extreme events. In such a context, seasonal forecasts (i.e., climate predictions from a few weeks to several months ahead) are compelling instruments able to anticipate upcoming climate risks and guide tactical decisions. In this study, we assess the performance of seasonal forecasts for the summer period across Central Europe and the Mediterranean region in predicting some key indicators serving agriculture and forestry sectors, i.e., Potential EvapoTranspiration (PET), Potential Soil Moisture Deficit (PSMD), and Fire Weather Index (FWI). We exploit authoritative climate data from Copernicus Climate Data Store, i.e., ERA5 reanalyses and hindcasts from CMCC SPSv3 and ECMWF SEAS5 seasonal prediction systems (SPSs), to evaluate, using both deterministic and probabilistic evaluation scores, differences in performance across the two SPSs, two start dates (March and May) and four correction techniques applied to overcome modelling bias, namely bias correction (BC), calibration (CAL), quantile mapping (QM) and detrending (DET). Results show that seasonal predictions of PET perform better in Western and Eastern Europe and some areas of North Africa. PSMD predictions follow a similar spatial pattern as PET, except that for some areas in Central (Eastern) Europe in which the performance increases (decreases). FWI predictions reveal better results in some areas of the Iberian Peninsula, North-Western Africa, Balkan Peninsula, and Ukraine. Results also suggest that QM might be the most suitable technique for bias correction. Furthermore, the start date of the forecast might imply varying correlation significance, with the start date closest to the forecasted period not always being the best. Overall, our study suggests the potential usefulness of seasonal forecasts for decision making under different geographical and environmental contexts, considering sensitivity inherent to different processing chains.

Potential soil moisture deficit: A useful approach to save water with enhanced growth and productivity of wheat crop

Abstract Wheat is the main crop in the world ranks after rice and the largest grain source of Pakistan. Among several reasons for diminishing wheat yield in Pakistan, water stress throughout the growing season decreases crop production because of the short life span. Two years (2015–16 and 2016–17) of field experiments were conducted to assess the impact of various water regimes (full irrigation, irrigation at 45, 60, and 75 mm potential soil moisture deficit (PSMD)) on the growth and yield of wheat. Maximum crop growth rate was recorded by application of irrigation at 45 mm PSMD. Application of irrigation at 45 mm PSMD ensured maximum radiation use efficiency regarding total dry matter production and grain yield. The maximum number of productive tillers, spike length, and grain yield were recorded under 45 mm PSDM treatment. The present results show that the effect of water is more pronounced regarding the growth and productivity of wheat. Application of irrigation at 45 mm PSMD ensures higher economical yield.

Combined Application of Potassium and Zinc Improves Water Relations, Stay Green, Irrigation Water Use Efficiency, and Grain Quality of Maize under Drought Stress

Maize (Zea mays L.) plays an important role in the global food security, but its production is threatened by climate change, especially drought stress. Potassium (K) and zinc (Zn) are considered useful to mitigate the negative consequences of drought stress in plants. Therefore, the objective of this two-year study was to identify the best combination of K and Zn application to improve the water relations, photosynthetic pigments, yield, irrigation water use efficiency (IWUE) and grain quality of maize sown under mild and severe drought stress conditions. The consisted of three drought stress levels viz. 1) well-watered as control (WW), 2) mild drought (MD) with 25 mm of potential soil moisture deficit (PSMD), 3) severe drought (SD) with 50 mm of PSMD and six K-Zn treatments: i.e. 125, 100 and 150 kg ha−1 K with 0 and 12 kg ha−1 Zn. The results indicated that K-Zn application improved the water relations and chlorophyll contents, biological yield and grain quality, irrespective of water stress treatment. The combined application of K-Zn under mild drought stress produced statistically same biological yield and grain quality as under well-irrigated without K-Zn fertilization and also produced compratively higher IWUE, biological yield and grain quality under sverer drought stress. Hence, the application of K at 150 kg ha−1 in combination with Zn at 12 kg ha−1 might be useful to improve the maize production and grain quality under drought stress. As IWUE was low in WW conditions, therefore, irrigation scheduling must be re-evaluated for optimum water use efficiency.

Estimation of spatially distributed groundwater potential recharge for the United Kingdom

The calculation of distributed recharge is necessary to drive numerical groundwater models used to manage and protect groundwater resources, to assess the impact of anthropogenic stresses and climate change, and to study the viability of technologies, such as exploiting the heat stored in the ground. A national-scale model allows policymakers and governmental decision-makers to set policy within the correct geographical context. However, many challenges are associated with building large-scale models, for example, the representation of processes on coarse grid resolution. This study presents distributed potential recharge values, calculated using the modified Environment Agency (EA)/Food and Agriculture Organization recharge algorithm. The model calibration is presented and the simulated potential recharge values and soil moisture deficit values are compared with estimates provided by the EA and the Meteorological Office (Met Office). Long-term average potential recharge values are very small in the east of the UK but they increase significantly towards the west and north, reaching values as high as 8 mm day −1 over the hills of Wales and Scotland. While this study highlights the need for further model refinement, the presented results are useful for assessing the potential recharge values at a national scale and for undertaking water resource studies, especially in catchments with unconfined/near-surface aquifers.

Quantification of Radiation Use Efficiency and Yield of Wheat as Influenced by Different Levels of Nitrogen and Water Stress under Semi-Arid Conditions of Faisalabad

Crop production is greatly influenced by water and nutrition stress in semi-arid areas. Nitrogen and water are two most important yield limiting factors which effect economic production of wheat. Drought initiates when large area of land suffers from absence of precipitation for temporary periods. Though, not only water scarceness but also low relative humidity and high temperature are other climate factors which induce drought condition. Whereas Effective nutrition (nitrogen) maintains crops metabolic activities and has the potential to lessen drought stress. According to study carried out to explore the influence of varying levels of potential soil moisture deficit (PSMD) and nitrogen, an experiment was planned at agronomy research area, University of Agriculture, Faisalabad. It was laid out in randomized complete block design (RCBD) with split plot arrangement, and replicated thrice. Two factors: potential soil moisture deficit levels (I1: irrigation at 50 mm PSMD, I2: irrigation at 75 mm PSMD and I3: irrigation at 100 mm PSMD) were randomized in main plots, while sub plot nitrogen levels {control (No nitrogen), 50, 100 and 150 kg N ha-1} were randomized. Adequate nitrogen application along with sufficient irrigation management gave highest yield. Under water deficit conditions adequate nitrogen application ameliorates the drought stress. Highest plant height (86.27 cm), number of productive tillers (320.0), grain·spike-1(49.73), test weight (50.55 g) and grain yield (6.72 t·ha-1) were observed with 75 mm PSMD and 150 kg·ha-1 application of nitrogen. While radiation use efficiency for dry matter accumulation of wheat ranged from 1.53 - 1.87 g·MJ-1 whereas, radiation use efficiency for grain yield ranged from 0.421 - 0.473 g·MJ-1. Results revealed that highest RUE obtained I3 (75 mm PSMD) and nitrogen application at 150 kg·ha-1. Judicial application of irrigation and fertilizer not only boosts the yield but also saves resource and increases former output.

Modeling the water and nitrogen productivity of sunflower using OILCROP-SUN model in Pakistan

Water and nitrogen (N) limitations in soil usually restrict plant growth hence reducing water and nitrogen productivity. Precise irrigation application is vital in water scarce areas of the world, such as Pakistan. Water and N are generally the most important factors in high yielding of crops. This interaction between irrigation levels and N can be analyzed through field experiments in concert with crop simulation models and decision support systems. Recently the use of crop growth models in crop husbandry has become more common to provide the decision support for farmers. The proposed study was conducted at Agronomic Research Area, University of Agriculture Faisalabad, Pakistan during the years 2012 and 2013 to evaluate OILCROP-SUN model under decision support system for agro-technology transfer (DSSAT) for simulating growth, development and achene yield of sunflower hybrid Hysun-33. The experiment was laid out using split plot design with four irrigation levels (control, 45, 60 and 75mm potential soil moisture deficit) in main plots and three N rates (90, 120 and 150kgha−1) in sub plots. The model was first calibrated with control irrigation plus 150kgNha−1 treatment (I1N3), then evaluated (2012) and validated (2013) by utilizing experimental data. The evaluation and validation exhibited that the model simulated anthesis date, maturity date, maximum leaf area index (LAI), total dry matter (TDM), achene yield and oil contents very well with an error of 0–6.15%, 0–3.96%, −25.14 to 6%, −0.37 to 17.75%, −4.58 to 17.12% and −15.04 to 12.15%, respectively. Similarly, root mean square error (RMSE) values for soil water and leaf N contents were ranged from 0.03 to 0.05cm3cm−3 and 0.16% to 0.71%, respectively. While RMSE for crop evapotranspiration (ET) was 29.87mm in 2012 and 32.56mm in 2013. The highest achene yield and oil contents were achieved with the control irrigation in combination of 150kgNha−1 application. However saving of water (110mm in 2012 and 120mm in 2013) with 45mm potential soil moisture deficit (PSMD) treatment (without significant reduction in sunflower productivity) recognized it as most suitable irrigation scheduling technique under water scarce areas of the world. The results disclosed that OILCROP-SUN model can be efficaciously used for simulation of spring sown sunflower under semi-arid conditions of Pakistan.

The Implications of Using Estimated Solar Radiation on the Derivation of Potential Evapotranspiration and Soil Moisture Deficit within an Embankment

In the absence of measured data, evapotranspiration is commonly estimated at a given site according to the methods outlined by Allen et al. (1998). Their work provides a system of calculation to derive the solar radiation values required to predict the available energy for water vaporisation. As such estimations of evapotranspiration are very dependent on the available data. In this work, meteorological parameters including air temperature, relative humidity, wind speed, near-surface soil temperature, shortwave and net solar radiation were measured for a complete year at the BIONICS trial embankment, Newcastle, UK.Estimates were made of the net radiation for a number of cases (1. no radiation data and 2. measured incident short wave radiation) and compared to the field monitored values. These data were in turn used to estimate the potential evapotranspiration (ETp) from the embankment. The results indicate that the net radiation and hence ETp derived entirely from estimated data are significantly higher than those derived with measured shortwave or net radiation. Results for estimates of ETp derived from monitored shortwave and net radiation data are a close match to each other.In order to investigate the potential effects on slope stability, an assessment of soil moisture deficit was undertaken. The results indicate that numerical models using the varying estimates of ETp would likely produce different results in terms of generated suctions and suction dissipation and so undergo different magnitudes of shrink-swell cycling, in turn leading to varying rates of strain softening behaviour, differing calculated factors of safety and differing modelled time to failure.

English

Wheat is a staple food of Pakistan and its productivity is linked with water supply. Potential soil moisture deficit (PSMD) is an approach to save water. PSMD technique was utilized to grow early and late sowing wheat (Triticum aestivum L.) for optimum yield. The experiment was conducted at the agronomic research area, University of Agriculture, Faisalabad during 2010‒2011 and 2011‒2012. The experimental design was randomized complete block design in a split plot arrangement with three replications. The main plot was sowing dates (15 November and 15 December) and the sub-plots were levels of irrigation based on PSMD (full irrigation, 45 mm, 60 mm and 75 mm). The row spacing as set 20 cm and the seed rate was 125 kg ha using cv. Sahar-2006. Fertilizer was applied at 120:90 kg ha of nitrogen and phosphorus, respectively. Data were recorded for yield and yield components at maturity. Irrigation at 45 mm PSMD for crop sown on November 15 produced maximum grain yield. During both years, maximum plant height, number of grains per spike, thousand grain weight, productive of tillers (m), grain yield and WUE were recorded with full irrigation and irrigation at 45 mm PSMD respectively. Results revealed that deficit irrigation at 45 mm PSMD was water saving as compared to farmer conventional practice of full irrigation. © 2016 Friends Science Publishers

Probabilistic soil moisture projections to assess Great Britain’s future clay-related subsidence hazard

Clay-related subsidence is Great Britain’s (GB) most damaging soil-related geohazard, costing the economy up to £500 million per annum. Soil-related geohazard models based on mineralogy and potential soil moisture deficit (PSMD) derived from historic weather data have been used in risk management since the 1990s. United Kingdom Climate Projections (UKCP09) suggest that regions of GB will experience hotter, drier summers and warmer, wetter winters through to 2050. As a result, PSMD fluctuations are expected to increase, exacerbating the shrinkage and swelling of clay soils. A forward-looking approach is now required to mitigate the impacts of future climate on GB’s built environment. We present a framework for incorporating probabilistic projections of PSMD, derived from a version of the UKCP09 stochastic weather generator, into a clay subsidence model. This provides a novel, national-scale thematic model of the likelihood of clay-related subsidence, related to the top 1–1.5 m soil layer, for three time periods; baseline (1961–1990), 2030 (2020–2049) and 2050 (2040–2069). Results indicate that much of GB, with the exception of upland areas, will witness significantly higher PSMDs through to the 2050s. As a result, some areas with swelling clay soils will be subject to proportionately increased subsidence hazard. South-east England will likely incur the highest hazard exposure to clay-related subsidence through to 2050. Potential impacts include increased incidence of property foundation subsidence, alongside deterioration and increased failure rates of GB’s infrastructure networks. Future clay-subsidence hazard scenarios are beneficial to many sectors, including: finance, central and local government, residential property markets, utilities and infrastructure operators.

Predicting the water retention characteristics of UK mineral soils

SummaryThe management of water resources in compliance with regulatory requirements increasingly uses national environmental impact assessments incorporating models of soil solute transport. Most such models use either continuous functions designed to solve the Richards equation, or capacity‐type functions based on water contents between specified soil water pressure heads. The work described here has used three separate sets of measured water‐release data representative of the whole of the UK to develop a set of pedotransfer functions (PTFs) for predicting volumetric water contents at seven pressure heads on the water release curve ranging from 0 to −1500 kPa. A theoretically‐based structural stratification of the data was proposed and tested. Within each grouping, multiple regression analysis was used to derive equations for predicting the water contents at each pressure head, based on a selected set of predictors. The resulting PTFs gave a significantly better prediction than PTFs derived from the unstratified data and also than the widely used HYPRES PTFs. For all non‐sandy horizons not subject to regular cultivation, additional PTFs incorporating a climatic variable, the average annual potential soil moisture deficit (PSMD) gave a further improvement in prediction in drier areas of the UK with PSMD greater than 130 mm. Mean errors associated with using the PTFs to parameterize continuous function models and a capacity model for calculating water availability for cereals (APcereals) are ±16.4 and 16.9%, respectively.

Impact of nitrogen nutrition and moisture deficits on growth, yield and radiation use efficiency of wheat (Triticum aestivum L.)

Crop production in arid and semi arid areas is restricted by soil deficiencies in moisture and plant nutrients, especially nitrogen. In order to evaluate the impact of nitrogen nutrition and moisture deficits on growth, yield and radiation use efficiency of wheat ( Triticum aestivum L.), a field experiment was conducted at Agronomic Research Area, University of Agriculture Faisalabad, during 2008 to 2009. The study comprised of four nitrogen levels, that is, N 0 = control, N 1 = 60, N 2 = 120 and N 3 = 180 kg N ha -1 and three water deficit levels, that is, I 1 = irrigation at 25 mm potential soil moisture deficit (PSMD), I 2 = irrigation at 50 mm potential soil moisture deficit (PSMD), I 3 = irrigation at 75 mm potential soil moisture deficit (PSMD). Results of the study revealed that maximum grain yield (6.72 t ha -1 ) was obtained in the case of N 3 (180 kg N ha -1 ) when I 2 = irrigation at 50 mm potential soil moisture deficit (I 2 × N 3 ) was applied in contrast to lowest grain yield (2.00 t ha -1 ) in response to I 3 = irrigation at 75 mm potential soil moisture deficit × no nitrogen (control) (I 3 × N 0 ). Highest plant height (86.27 cm), number of spike bearing tillers m -2 (320), grains per spike (49.73), 1000-grain weight (50.55 g), biological yield (15.48 t ha -1 ), straw yield (8.76 t ha -1 ) and harvest index (43.42%) increased with increasing levels of nitrogen. The maximum value of these parameters was also observed in I 2 where irrigation was applied at 50 mm potential soil moisture deficit. The maximum value of RUE for TDM (6.45 g MJ -1 ) was observed in I 2 × N 3 irrigation at 50 mm potential soil moisture deficit and nitrogen (180 kg ha -1 ) treatment combination. Similarly, maximum RUE for grain yield (2.80 g MJ -1 ) was observed for nitrogen (50 mm potential soil moisture deficit and 180 kg N ha -1 ). Keywords: Wheat, nitrogen nutrition, moisture deficits, radiation use efficiency, yield, Triticum aestivum L.

Is UK biofuel supply from Miscanthus water‐limited?

AbstractSustainable Miscanthus plantings encouraged under publicly funded schemes should be based on sound economic and environmental assessments. We developed an empirical yield model for Miscanthus from harvestable dry matter yields at 14 field trials in the UK to estimate site‐specific and regional yields derived from meteorological variables and soil available water. Harvestable yields of crops established for at least 3 years at 14 arable sites across the UK ranged from 5 to 18 t/ha, averaging at 12.8 (±2.9) t/ha. Variables considered to affect yield were number of years after planting, length of season (Tair > 9 °C), temperature, global solar radiation, precipitation and potential evapotranspiration during the season, and soil available water capacity (AWC). At a single site (Rothamsted), AWC and the relative average potential soil moisture deficit during the main growing season explained 70% of annual yield variation (RMSE = 1.38 t/ha, P < 0.001). For the complete UK data set (n = 67), yield variation was related to AWC, air temperature and precipitation (RMSE = 2.1 t/ha, P < 0.01). Linking soil survey and spatially interpolated weather data we calculated an overall national average dry matter yield of 9.6 t/ha. As shown for two counties (Oxfordshire and North Yorkshire), estimated yield may decrease by 1 t/ha, and its uncertainty may rise from 15 to >20%, when soil survey instead of local soil data are used. Using data from a single weather station can introduce a bias (<1 t/ha) because of differences in elevation and local temperature and precipitation. Overall, it seems most important for bioenergy plantings to assure sufficient water supply from the soil (AWC > 150 mm) during the main growing season.

Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado

The nature of the snowpack has the potential to strongly influence the patterns of alpine plant productivity and composition by governing soil moisture levels, growing season duration and the thermal regime of alpine soils. This study evaluates these relationships by modeling the interrelationships of snow depth, snow water equivalent (SWE), snow disappearance rate, soil moisture, attributes of the alpine plant community and selected terrain factors using decision‐tree techniques at Niwot Ridge, Colorado Front Range. The modeling results showed a strong correlation (r2 > 0.9, P < 0.001) between the snow disappearance rate and SWE and terrain factors that control the degree of shelter and exposure of a given local and elevation. The model was sufficiently robust to predict the spatial distribution of the snowpack for 12 years that exhibited average snow fall (r2 = 0.8, P < 0.001), but yielded lower correlation (r2 = 0.2, P < 0.001) in drought years. Soil moisture was significantly correlated (r2 = 0.7, P < 0.001) with snow‐fall amounts and terrain factors; however, meltwater and summer rain offset the potential soil moisture deficit in windward sites. Annual plant biomass did not correlate well with snow attributes and soil moisture because the cascading impact of topography on snowpack and soil moisture was not well captured by measurements of aboveground biomass. In contrast, the species richness index was significantly correlated with snow depth and soil moisture (r2 = 0.7, P < 0.001), thereby demonstrating the importance of snow on some attributes of the alpine plant community.

Soil moisture mediates association between the winter North Atlantic Oscillation and summer growth in the Park Grass Experiment

Several aspects of terrestrial ecosystems are known to be associated with the North Atlantic Oscillation (NAO) through effects of the NAO on winter climate, but recently the winter NAO has also been shown to be correlated with the following summer climate, including drought. Since drought is a major factor determining grassland primary productivity, the hypothesis was tested that the winter NAO is associated with summer herbage growth through soil moisture availability, using data from the Park Grass Experiment at Rothamsted, UK between 1960 and 1999. The herbage growth rate, mean daily rainfall, mean daily potential evapotranspiration (PE) and the mean and maximum potential soil moisture deficit (PSMD) were calculated between the two annual cuts in early summer and autumn for the unlimed, unfertilized plots. Mean and maximum PSMD were more highly correlated than rainfall or PE with herbage growth rate. Regression analysis showed that the natural logarithm of the herbage growth rate approximately halved for a 250 mm increase in maximum PSMD over the range 50-485 mm. The maximum PSMD was moderately correlated with the preceding winter NAO, with a positive winter NAO index associated with greater maximum PSMD. A positive winter NAO index was also associated with low herbage growth rate, accounting for 22% of the interannual variation in the growth rate. It was concluded that the association between the winter NAO and summer herbage growth rate is mediated by the PSMD in summer.

Water-use efficiency and the effect of water deficits on crop growth and yield of Kabuli chickpea (Cicer arietinum L.) in a cool-temperate subhumid climate

The present study was conducted from 1998 to 2000, to evaluate seasonal water use and soil-water extraction by Kabuli chickpea (Cicer arietinum L.). The response of three cultivars to eight irrigation treatments in 1998/99 and four irrigation treatments in 1999/2000 at different growth stages was studied on a Wakanui silt loam soil in Canterbury, New Zealand. Evapotranspiration was measured with a neutron moisture meter and water use efficiency (WUE) was examined at crop maturity. Water use was about 426 mm for the fully irrigated treatment and at least 175 mm for the non-irrigated plants. There was a significant correlation (P<0·001) between water use and biomass yield (R2=0·80) and water use and seed yield (R2=0·75). There were also highly significant (P<0·001) interacting effects of irrigation, sowing date and cultivar on WUE and the trend was similar to that for seed yield. The estimated WUE ranged from 22–29 kg DM/ha per mm and 10–13 kg seed yield/ha per mm water use.The three chickpea cultivars were capable of drawing water from depths greater than 60 cm. However, most of the water use (0·49–0·93 mm/10 cm soil layer per day) came from the top 0–30 cm, where most of the active roots were concentrated. The study has shown that using actual evapotranspiration and water-use efficiency, the biomass yield and seed yield of Kabuli chickpeas can be accurately predicted in Canterbury. Soil water shortage has been identified as a major constraint to increasing chickpea production. Drought was quantified using the concept of maximum potential soil moisture deficit (Dpmax) calculated from climate data. Drought responses of yield, phenology, radiation use efficiency and yield components were determined, and were highly correlated with Dpmax. The maximum potential soil moisture deficit increased from about 62 mm (irrigated throughout) to about 358 mm (dryland plots). Chickpea yield, intercepted radiation and the number of pods per plant decreased linearly as the Dpmax increased. Penman's irrigation model accurately described the response of yield to drought. The limiting deficit for this type of soil was c. 165 and 84 mm for the November and December sowings in 1998/99 and 170 mm in 1999/2000. Beyond these limiting deficits, yield declined linearly with maximum potential soil moisture deficits of up to 358 mm. There was little evidence to support the idea of a moisture sensitive period in these Kabuli chickpea cultivars. Yield was increased by irrigating at any stage of crop development, provided that the water was needed as determined by the potential soil moisture deficit and sowing early in the season.

Climate reality - actual and expected

New Zealand average surface temperatures have increased by 0.7 °C since 1871. In the last quarter of the 20th century, more prevalent west to southwest flows occurred, accompanying a higher incidence of El Niño events. This resulted in annual rainfall decreasing in eastern areas of the North Island. As well as the global warming signal, interannual to decadal climate variability is a strong feature of east coast dryland climates. The El Niño-Southern Oscillation, (ENSO), through El Niño/ and La Niña episodes, drives climate variability seasonally. The recently described Interdecadal Pacific Oscillation (IPO) shifts climate every one to three decades and changes precipitation averages in these areas. These features of the climate system leave east coast dryland farming open to considerable climate variability. Records of potential soil moisture deficit (PSMD) around Napier and Ashburton show that significant PSMD developed in these regions by 1 December, in 50 to 85% of years with severe deficits in 20 to 55% of years. These deficits build as summer progresses. El Niño events intensify, whilst La Niña episodes normally ameliorate these conditions on seasonal time scales. The IPO climate shifts significantly change the dryness of the soil of these areas, with the transition from negative to positive phases increasing PSMD by 35 to 50 mm. Climate change over the next few decades will be driven by the underlying trend of global warming. For New Zealand, this will be a warming of about 0.2 °C per decade. The latest scenarios and climate model results indicate that westerly circulation is likely to strengthen over New Zealand, with a drying of east coast climate in the order of 10% by 2080. These will cause an increase in PSMD in the order of 20 to 30%. ENSO and IPO variability will be a continuing feature of New Zealand climate in coming decades. East coast dryland farms experience substantial climate variability. As climate warming continues in the decades of the 21st century, these areas will become increasingly stressed as potential evapotranspiration (PET) rates increase, particularly when the IPO next changes phase and during El Niño events. Climate forecasting is an exciting new technology that will give farmers early warning and increase preparedness for dry seasons ahead, allowing them to make key strategic decisions. A mixture of new and traditional technologies will also assist, such as intercropping and use of seasonal climate forecasting. Despite this, dryland farming systems are likely to become increasingly limited owing to low rainfall and high potential evapotranspiration rates.

Spatio-temporal modelling of broad scale heterogeneity in soil moisture content : a basis for an ecologically meaningful classification of soil landscapes

We describe the classification of landscapes characterised bymineral soil using a model that calculates soil moisture availability on amonthly basis. Scotland is used as a case study area. The model uses potentialsoil moisture deficit, estimated using broad scale (40 × 40 km)climate patterns, in conjunction with meteorological station measurements toobtain finer scale values of climatic soil moisture deficit. Point estimates ofsoil available water are obtained for soil characteristics using appropriatepedotransfer functions, and geostatistical techniques are used to upscale theresults and interpolate to a 1-km grid. Known heterogeneityin soil physical characteristics is used to provide local corrections to thepotential soil moisture deficit, estimated using the climatic variables above.Temporal profiles of monthly water content are modelled for each1-km location and classified into six classes usingunsupervised cluster analysis. The spatial distribution of these classesreflects regional variations in the availability of moisture and energy, onwhich finer-grained topographic patterns are superimposed. In the case study,the broad scale spatial heterogeneity of heathlands and grasslands on mineralsoils in Scotland is shown to be strongly related to the soil moistureclassification. The results can be used in studies investigating the patternsofdistribution of communities at the landscape and regional scale.