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Aggregation is an important factor among physical soil parameters and affects soil quality. In this study, some soil physical (field capacity, wilting point and sand, silt and clay contents), chemical (pH, electrical conductivity, CaCO3, organic matter and exchangeable Na, Ca, Mg and K) and biological properties (CO2 from respiration and urease, dehydrogenase, β-glucosidase, alkaline phosphatase and acid phosphatase activities) were examined. Some of these properties were eliminated by principal component and clustering analyses to create a minimum dataset. Correlations were evaluated between selected properties and the percentage aggregation of micro ( 0.05). In general, the highest correlation for micro aggregation was with enzyme activity.

Although climate change is expected to affect the ecology of many weed species, the nature and scale of these responses is presently not well defined. This presages a suite of potential problems for the agricultural industries. Consequently, we investigated the effects of anticipated climate change on biomass and seed production, for two varieties of wild sage, Salvia verbenaca L. var. verbenaca and Salvia verbenaca var. vernalis Bioss. For the investigation, ambient (400 ppm) and elevated (700 ppm) carbon dioxide conditions, in combination with well-watered (100% field capacity) and drought conditions (60% field capacity), were selected to represent alternative climate scenarios. The alteration in biomass production was represented by a combined measurement of nine variables; plant height, stem diameter, number of leaves, number of branches, leaf area, leaf thickness, shoot biomass, root biomass and dry leaf weight, and fecundity was measured via two variables; 100 seed weight and number of seeds per plant. All biomass measurements were reduced in a drought situation compared with well-watered conditions in ambient carbon dioxide (400 ppm), and each corresponding measurement was greater under elevated carbon dioxide (700 ppm) regardless of water treatment. In contrast, this was not observed for 100 seed weight or number of seeds per plant. Although a similar profile of a reduction in fecundity parameters was observed under drought conditions compared with well-watered conditions in ambient carbon dioxide, there was an increase in seed mass only for var. verbenaca under elevated carbon dioxide in both water treatments. In addition, there was a very small increase in the number of seeds in this species under drought conditions in elevated carbon dioxide, with neither increase in seed mass or seed number being observed in var. vernalis. These results suggest that although future climate change may result in increased competition of both these varieties with desirable plants, their management strategies will need to focus on effects of increased size of the weeds, rather than only attempting to reduce the seed bank holdings.

Nitrous oxide (N2O), a greenhouse gas, contributes to stratospheric ozone depletion. Agricultural fertiliser use and animal excreta dominate anthropogenic N2O emissions. Soil relative gas diffusivity (Dp/Do) has been used to predict the likelihood of soil N2O emissions, but limited information exists about how soil N2O emissions vary with soil type in relation to Dp/Do. It was hypothesised that, regardless of soil type, the N2O emissions would peak at the previously reported Dp/Do value of 0.006. Four pasture soils, sieved and repacked to three different bulk densities, were held at nine different soil matric potentials between near saturation and field capacity. Soil nitrate and dissolved organic matter concentrations were adequate for denitrification at all soil matric potentials. Increasing soil bulk density and soil matric potential caused Dp/Do to decline. As Dp/Do declined to a value of 0.006, the N2O fluxes increased, peaking at Dp/Do ≤ 0.006. This study shows that the elevation of N2O fluxes as a Dp/Do threshold of 0.006 is approached, holds across soil types. However, the variability in the magnitude of the N2O flux as Dp/Do declines is not explained by Dp/Do and is likely to be dependent on factors affecting the N2O:(N2O + N2) ratio.

Water availability in soil modulates plant acclimatisation responses in different habitats. In this study, we evaluated the effect of water deficit on the physiological, biochemical and growth responses of Vachellia farnesiana. Open environment experiment was conducted during 90 days and two conditions of hydration were tested: full hydration (H) and water deficit (WD) at 25% of field capacity. The relative water content (RWC) of the leaves under WD showed a 30.2% decrease (P < 0.01), compared with the hydrated plants at 30 days. A decrease in the RWC led to decrease in the osmotic potential (Ψs), quantum yield of PSII (Fv/Fm) and lesser content of chlorophylls a and b under WD. A greater carotenoid content and simultaneous increase in the content of proline, H2O2 and phenolic compounds of the leaves was also observed in WD. Water deficit also promoted differences in the nitrogen, phosphorus, and potassium content of the leaves when compared with hydrated plants. Although they showed growth deficit, plants of V. farnesiana demonstrated resistance to WD through physiological and biochemical adjustments.

There is currently relatively little available information on subsoil phosphorus (P) use for crop production as a function of soil order. In this study, a rhizobox experiment was performed using subsoils of two reference soil groups, an Orthic Ferralsol and a Haplic Luvisol. To evaluate the immediate P uptake by wheat (Triticum aestivum L.) from different subsoil P pools during 14 days of growth, subsoil bands were spiked with KH2PO4 solution associated to Fe-hydroxide (33P-Fe), to Al-hydroxide (33P-Al), in free form (33P-OrthoP), or in trace amounts without any additional 31P (33P-NoP). At the beginning of the experiment, the soil water content was set at 75% of water-holding capacity, corresponding to an initial soil matric potential of −12 ± 1 kPa. During plant growth, soil moisture decreased in both soils, but soil matric potentials in both soils did not drop below field capacity (−33 kPa; pF 2.5). The shoot dry weights of the Ferralsol were 1.2 to 1.8 times those of the Luvisol. Despite elevated soil P availability in the Luvisol, shoot P concentrations did not differ between the two soils. The amount of 33P taken up by the shoots from the oxide phases was 15% to 40% greater in the Ferralsol treatments than in those in the Luvisol treatments. It was concluded that the more favourable physical soil conditions facilitated 33P uptake from both oxidic phases from the Ferralsol subsoil relative to the Luvisol subsoil, despite better P phytoavailability in the latter.

Soil rewetting can induce a flush of organic matter mineralisation, but the factors underpinning this mineralisation response are poorly understood. We investigated the effects of antecedent soil water content, before rewetting, on the quantity, quality and biodegradability of dissolved organic matter present in the leachate pore volumes from a soil under two different management histories: arable and grassland. Soils were collected at field capacity (FC) and dried to give four soil gravimetric water contents (θg): 22% (not dried, left at FC), 15%, 8% and

Denitrification is sensitive to changes in soil physical properties that affect solute transport, air content and gas diffusion. Using lysimeters, containing intact soil from intensively tilled (IT) and no-tilled (NT) soil used to grow forage crops, we examined how simulated animal treading at different moisture contents (above and below field capacity; >FC and FC greatly increased denitrification, especially from IT soil and produced the greatest amount of N2 (64kg N ha–1), N2O (8.2kg N ha–1), as well as the lowest N2O to N2O+N2 ratio (0.08) and NO3 leaching (136kg N ha–1 below 30cm). In both the uncompacted or compacted soils FC. Treading at

Wildfires commonly increase nutrient, carbon, sediment and metal inputs to streams, yet the factors responsible for the type, magnitude and duration of water quality effects are poorly understood. Prior work by the current authors found increased nitrogen, phosphorus and cation exports were common the first 5 post-fire years from a synthesis of 159 wildfires across the western United States. In the current study, an analysis is undertaken to determine factors that best explain post-fire streamwater responses observed in those watersheds. Increased post-fire total nitrogen and phosphorus loading were proportional to the catchment extent of moderate and high burn severity. While post-fire dissolved metal concentrations were correlated with pre-fire soil organic matter. Total metal concentration increased where post-fire Normalised Difference Vegetation Index, a remote sensing indicator of live green vegetation, was low. When pre-fire soil field capacity exceeded 17%, there was a 750% median increase in total metals export to streams. Overall, the current analysis identified burn severity, post-fire vegetation cover and several soil properties as the key variables explaining extended post-fire water quality response across a broad range of conditions found in the western US.

Subsoil compaction is a serious long-term threat to soil functions. Only a few studies have quantified the mechanical stresses reaching deep subsoil layers for modern high wheel load machinery. In the present study we measured the vertical stresses in the tyre–soil contact area and at 0.3, 0.6 and 0.9 m depths of a sandy loam soil at field capacity water content. The soil was ploughed annually to a depth of 0.25 m and was tested in the spring following autumn ploughing but before secondary tillage. The machinery tested was a tractor–trailer system for slurry application with a total weight of 52 Mg. Wheel loads ranged from approximately 20 to 70 kN. The tyres were all radial ply with volumes ranging from 0.63 to 1.23 m3. The tyre inflation pressures were generally above those recommended by the manufacturer and ranged from 170 to 280 kPa. The stress distributions in the contact area were highly skewed. Across tyres, the maximum stress in the contact area correlated linearly with, but was much higher than, the mean ground pressure. For each of the three soil depths, the maximum stresses under the tyres were significantly correlated with the wheel load, but not with other loading characteristics. The data predict a 6.6-kPa increase in vertical stress at 0.9 m depth for each 1-Mg addition to the wheel load. The soil stress observations support a simple rule of thumb combining wheel load and inflation pressure in calculation of subsoil vertical stress. We measured vertical stresses up to 300, 100 and 45 kPa at soil depths of 0.3, 0.6 and 0.9 m respectively. Comparing these with the data in the literature regarding soil strength and measured compaction effects on the soil studied, we conclude that the traffic event investigated is likely to induce serious effects on soil properties and functions to a depth of at least 0.7 m.

Planting of forage can alleviate grazing pressure on natural ecosystems. In the Inner Mongolian environment, higher forage yields can be expected under irrigation because water is a key factor that limits plant growth. Lower grass yield caused by land degradation and climatic change highlight the potential importance of irrigated forage for maintaining livestock production in this environment. The present study in the Xilingol area of Inner Mongolia aimed to identify forage varieties producing high-yielding, quality forage. Three lucerne (alfalfa) varieties (Medicago sativa L. cvv. Aohan and Zhaodong, Medicago varia Martyn) and a grass (Elymus nutans Griseb) were assessed. Irrigation commenced when soil moisture at 10 cm depth reached the wilting coefficient, and ceased when soil reached field capacity. After 4 months, irrigation had significantly increased specific leaf area, tiller numbers and yield under irrigation (P

The present study evaluated responses of soil enzyme activity, soil micro-organisms, muskmelon root growth and muskmelon fruit yield and quality to different levels of film covering (full, half and no plastic film covering), drip pipe density (one pipe for one row (T1), three pipes for four rows (T3/4) and one pipe for two rows (T1/2)) and different lower limits of irrigation (60%, 70% and 80% of field capacity) in a greenhouse experiment using an orthogonal experimental design. Half film mulch cover resulted in higher muskmelon root activity (second only to full film covering) during the fruit swelling growth stage and promoted soil micro-organism growth. Compared with full and no film cover conditions, under half film cover mean soil urease activity was 25.16% and 1.46% higher, alkaline phosphatase (ALP) activity was 18.42% and 16.89% higher and catalase activity was 24.20% and 17.24% higher respectively. Compared with T1 and T3/4, under T1/2 mean soil ALP activity was 22.36% and 5.76% higher, catalase activity was 2.45% and 10.57% higher and muskmelon root activity during the fruit swelling period was 1.13- and 3.98-fold higher respectively. Irrigation at both 60% and 80% of field capacity improved muskmelon root length and area, soil micro-organism populations and soil urease, ALP and catalase activity. In addition, half film covering, irrigation at 80% field capacity and T1/2 improved the partial factor productivity for nitrogen, yield and fruit quality of muskmelons in the greenhouse. Therefore, these conditions appear to be the most appropriate agronomic configuration for muskmelon cultivation in greenhouses.

Conventional soil mapping uses field morphological observations to classify soil profiles into predefined classification systems and extrapolates the classified soils to make a map based on aerial photographs and the experience of the surveyor. A criticism of this approach is that the subjectivity of the surveyor leads to non-reproducible maps. Advances in computing and statistical analysis, and an increased availability of ancillary data have cumulatively led to an alternative, referred to as digital soil mapping (DSM). In this research, two agriculturally productive areas (i.e. Warren and Trangie) located in central New South Wales, Australia, were considered to evaluate whether pedoderms and soil profile classes defined according to the traditional approach can also be recognised and mapped using a DSM approach. First, we performed a fuzzy k-means analysis to look for clusters in the ancillary data, which include data from remote-sensed gamma-ray (γ-ray) spectrometry and proximal-sensed electromagnetic (EM) induction. We used the residual maximum likelihood method to evaluate the maps for various numbers of classes (k = 2–10) to minimise the mean square prediction error (σ2p,C) of soil physical (i.e. clay content, field capacity (FC), permanent wilting point (PWP) and available water content (AWC)) and chemical (pH, EC of 1 : 5 soil water extract (EC1:5) and cation exchange capacity (CEC)) properties of topsoil (0–0.3 m) and subsoil (0.6–0.9 m). In terms of prediction, the calculated σ2p,C was locally minimised for k = 8 when accounting for topsoil clay, FC, PWP, pH and CEC, and subsoil FC, EC1:5 and CEC. A comparison of σ2p,C of the traditional (seven pedoderm components) and DSM approach (k = 8) indicated that only topsoil EC1:5 and subsoil pH was better accounted for by the traditional approach, whereas topsoil clay content, and CEC and subsoil clay, EC1:5 and CEC were better resolved using the DSM approach. The produced DSM maps (e.g. k = 3, 6 and 8) also reflected the pedoderm components identified using the traditional approach. We concluded that the DSM maps with k = 8 classes reflected the soil profile classes identified within the pedoderms and that soil maps of similar accuracy could be developed from the EM data independently.

Plant growth and production are greatly affected by water deficit worldwide and particularly in Tunisia. In this context, a study was conducted to analyse the response of three vetch species (Vicia narbonensis, V. sativa and V. villosa) to four water treatments: 100% (Control), 80%, 60% and 40% of field capacity. Water stress led to important changes of both leaf physiology and anatomy. V. narbonensis kept cells turgor by adjusting the osmotic potential without changes in cell walls elasticity. V. sativa showed the most pronounced reductions of leaf water potential and the lowest osmotic adjustment under water stress although cell walls elasticity has not changed. However, V. villosa kept a higher fraction of apoplastic water over V. sativa that allowed it to maintain cells turgor despite the rigidity of its cell walls. Drought did not affect lamina thickness but increased the palisade parenchyma at the expense of spongy parenchyma. It was characterised by leaf lamina increase and constant thickness of the spongy parenchyma: a strategy to cope with drought. Moreover, stomata were reduced in size but were increased in number in order to avoid water loss.

This paper studies the spatial variation of topsoil moisture within different soil types in a medium-size catchment at the Spanish Pre-Pyrenees (Estaña catchment, 2.5 km2) using seasonal data at high spatial resolution. Topsoil moisture was measured with a Delta-T Theta Probe ML2x device up to 8 cm of soil depth and at seasonal scale during 2005 and 2006. Measured values were related to the soil water content at field capacity to calculate the relative topsoil moisture (θR, %). The highest values of θR were obtained in autumn (53.2%) and the lowest in summer (32.1%) showing a positive correlation with seasonal precipitation and an inverse relationship with seasonal solar radiation (SR). Steep northern slopes presented the highest values of θR in spring, summer and winter and topsoil moisture progressively decreases from steep northern slopes to gentle slopes and from gentle slopes to steep southern slopes, defining a topographical trend. Any topographical trend was observed in autumn when values of θR were very high within the whole catchment. No significant correlation was found between values of θR and those of topographic wetness index (TWI) except in summer. Relative topsoil moisture varied greatly for the different soil types and the highest values were also measured in steep northern slopes in spring, summer and winter. Correlation between θR and SR was good for the different soil types in winter when SR varied the most for the different physiographic units and the range of values of θR is the highest. No significant correlation was found in autumn for any soil type due to the very low values of solar radiation. Results of this work draw attention to the importance of considering the slope steepness and aspect conditions for a more precise characterization of moisture-sensitive areas in Mediterranean environments and soils at seasonal scale., This research was financially supported by the following project: “Soil erosion and carbon dynamic in Mediterranean agroecosystems: radioisotopic modelling at different spatial and temporal scales” (MEDEROCAR, CGL2008-00831/BTE) funded by the Spanish Ministry of Science and Innovation.

10 pages, 4 figures, We designed and tested an automatic irrigation control system for fruit tree orchards, designated CRP. At the end of each day, the device calculates the irrigation dose (ID) from sap flow readings in the trunk of trees irrigated to replenish the crop water needs, relative to similar measurements made in over-irrigated trees. It then acts on the pump and electrovalve to supply an ID sufficient to keep the soil close to its field capacity during the irrigation period. Remote control of the system is possible from any computer or Smartphone connected to the Internet. We tested the CRP in an olive orchard in southern Spain. The device was robust and able to filter and amplify the output voltages of the heat-pulse velocity probes and to calculate reliable sap flow data. It calculated and supplied daily irrigation amounts to the orchard according to the specified irrigation protocol. The remote control facility proved to be useful for getting real-time information both on the CRP behaviour and the applied IDs, and for changing parameters of the irrigation protocol. For our conditions, olive trees with big root systems growing in a soil with a remarkable water-holding capacity, the approach mentioned above for calculating ID had not enough resolution to replace the daily crop water consumption. The device, however, was able to react when the soil water content fell below the threshold for soil water deficit. The threshold value was identified with simultaneous measurements of stem water potential in the instrumented trees. Our results suggest a change in the irrigation protocol that will allow the CRP to apply a recovery irrigation whenever that threshold is reached, making the device suitable for applying a deficit irrigation strategy in the orchard., This work was funded by the IFAPA, Consejería de Innovación, Ciencia y Empresa de la Junta de Andalucía, research project ref. C03-056, and by the research project CICYT/FEDER AGL2004-0794-CO3-02/AGR.

Studying plants’ capability to adapt and recover from drought stress is essential because of the ever-changing nature of drought events. To evaluate the genotypically variable morpho-physiological adaptations to drought stress and recovery after re-watering, two wheat cultivars (Luhan-7 and Yangmai-16) were pot-cultured under three levels of water stress: severe (35–40% field capacity, FC) and moderate water deficits (55–60% FC) and well-watered conditions. Drought stress was applied at tillering (Feekes 2 stage) and jointing (Feekes 6 stage), respectively, followed by re-watering, and we observed changes in leaf characteristics, growth and physiological activities during water stress and rewatering periods as well as final grain yield traits at maturity. Results showed that drought stress adaptability associated with reduced leaf area, higher leaf thickness, chlorophyll, leaf dry matter and maintenance of leaf water potential were more strongly pronounced in Luhan-7 than in Yangmai-16. Under moderate stress both cultivars exhibited a small decrease in leaf gas-exchange and chlorophyll fluorescence activities, followed by rapid recovery. Under severe drought stress, Yangmai-16 displayed relatively less adaptability to drought, with a slower recovery after re-watering and a greater decrease in grain yield. It was concluded that even though crop growth rate completely recovered after re-watering, the final dry matter and grain yield outcomes were affected by pre-drought stress, and were dependant on the drought intensity, adaptability and recovery differences of the cultivars and growth stage. It was also concluded that genotypic variations in adaptability and recovery from drought stress are the indicators of drought tolerance and grain yield sustainability in wheat.

Tropical forests play a key role in the global carbon cycle. However, little is known about carbon cycling in the substantial portion of tropical forests that are low-lying, with shallow and fluctuating water tables. This study aimed to determine what factors control emissions of CO2 from soil in a riparian rainforest in Queensland, Australia. Emissions were measured over the course of 1 year, using static chambers. Emission rates were significantly related to soil temperature (0–0.1 m depth), soil water content (0–0.12 m depth) and depth to water table. The most efficient linear model of emissions as a function of measured parameters, which also included soil pH (0–0.1 m depth), had r2 = 0.355. CO2 emissions were highest (5.2–7.5 μmol m–2 s–1) at moderate soil temperature (24−28°C), water table depth (0.2–1.5 m) and soil water-filled porosity (0.25–0.79). They were lowest (

The greenhouse gas fluxes and effective mitigation strategies in subtropical vegetable cropping systems remain unclear. In this field experiment, nitrous oxide (N2O) and methane (CH4) fluxes from an irrigated lettuce cropping system in subtropical Queensland, Australia, were measured using manual sampling chambers. Four treatments were included: Control (no fertiliser), U100 (100 kg N ha–1 as urea), U200 (200 kg N ha–1 as urea) and N100 (100 kg N ha–1 as nitrate-based fertilisers). The N fertilisers were applied in three splits and irrigation was delivered sparingly and frequently to keep soil moisture around the field capacity. The cumulative N2O emissions from the control, U100, U200 and N100 treatments over the 68-day cropping season were 30, 151, 206 and 68 g N2O-N ha–1, respectively. Methane emission and uptake were negligible. Using N2O emission from the Control treatment as the background emission, direct emission factors for U100, U200 and N100 treatments were 0.12%, 0.09% and 0.04% of applied fertiliser N, respectively. Soil ammonium (NH4+) concentration, instead of nitrate (NO3–) concentration, exhibited a significant correlation with N2O emissions at the site where the soil moisture was controlled within 50%–64% water-filled pore space. Furthermore, soil temperature rather than water content was the main regulating factor of N2O fluxes in the fertilised treatments. Fertiliser type and application rates had no significant effects on yield parameters. Partial N balance analysis indicated that approximately 80% and 52% of fertiliser N was recovered in plants and soil in the treatments receiving 100 kg N ha–1 and 200 kg N ha–1, respectively. Therefore, in combination with frequent and low-intensity irrigation and split application of fertiliser N, substitution of NO3–-based fertilisers for urea and reduction in fertiliser N application rates were considered promising mitigation strategies to maintain yield and minimise N2O emissions during the low rainfall season.

Site-specific measurements of the apparent electrical conductivity (ECa) of soil using the EM38 were correlated with near-simultaneous neutron probe readings over periods of moisture extraction by an irrigated cotton crop. Thirty sites were monitored from three ECa zones within a 96-ha field of grey Vertosol soil 30 km west of Moree, New South Wales, Australia. This study differs from previous approaches by reporting the effect on ECa of a wetting front (irrigation) reaching a single ECa measurement point in a field and by using polyethylene neutron probe access tubes so that the EM38 could be operated directly over the same site measured by a neutron probe. We report strong correlations (r = 0.94) between neutron probe counts (CRR) averaged to a depth of 40 or 60 cm and ECa from an EM38 held in the vertical mode 20 cm above the soil surface. All combinations of EM sensor height (0–1.2 m) to neutron probe measurement depth (0.2–1.4 m) returned correlations >0.85. The relationship between CCR and ECa was linear for the purposes of estimating water content over a range of background ECa levels. More critical modelling suggested a slight curve (logarithmic model) fitted best. The range of surface-surveyed ECa from the start of irrigation (refill point) to fully irrigated (full point) was ~27 mS m–1 for this Vertosol, where surface ECa readings typically ranged from 50 to 200 mS m–1. We suggest that the calibration of ECa to CRR might be effected by a two-point measurement of the soil, namely at both upper (field capacity) and lower (wilting point) ECa values, and a site-specific calibration template generated by extending these point measures to whole-field surveys.

This paper presents findings of comparative evaluation of selected soil physical quality (SPQ) indicators, obtained from fields subjected to: >50 years of cultivation of three perennial pasture grasses (i) Digitaria smutsii (DS), (ii) Brachiaria decumbens (BD), and (iii) Andropogon gayanus (AG); (iv) >50 years of continuous cultivation (CC) of cereals–legumes; and (v) >20 years of natural fallow (NF). The study was aimed at identifying the land-use system having optimal values for SPQ. Fields under CC had the highest bulk density, and the lowest total porosity (PORt) and macroporosity (PORp), field capacity (FC), and available water capacity (AWC). Perennial pasture grasses fields had significantly higher organic carbon, PORt, FC, AWC, and saturated hydraulic conductivity, and, hence, had better SPQ than CC fields and, in some instances, NF fields. The usefulness of ratios FC/PORt = 0.66 and ACt/PORt = 0.34 as additional indicators for assessing soil response to land-use systems was not proven in this study, and therefore, further studies should be conducted on the subject matter. Pasture grasses improved SPQ values relative to continuous cereal–legume cropping and fallow. The SPQ under CC and NF fields might be best improved by applying organic matter.

Modelling soil water movement has increased the demand for accurate measurements of soil physical and hydraulic properties. Data on saturated hydraulic conductivity (K), which was measured by using different hydraulic heads, are presented for artificially packed soil columns and for different soil layers of undisturbed soil cores taken from a long-term experiment on conservation tillage. In the majority of the samples in both artificially packed soil columns and undisturbed soil cores, increasing hydraulic head caused significant deviation (i.e. significant positive correlation coefficient between hydraulic head and the measured values of K) from the conventional criterion for Darcy’s law that flux remains linear with hydraulic gradient. The study, therefore, emphasis the need to define the hydraulic head for measuring K values to be used for studying water movement in soils, to facilitate efficient utilisation of water resources for irrigating field crops in different soils and under different planting systems and irrigation methods.

Napier grass (Pennisetum purpureum Schumach.) is an important fodder and relatively drought-tolerant crop in tropical and subtropical regions, especially in developing countries. For this and other species, tools are needed for identifying drought-tolerant cultivars to aid selection for semi-arid environments. We determined tissue water status, carbon assimilation, biomass yield and forage quality for Napier grass cvv. Bana and Atherton grown in bins and subjected to three soil-water supply levels (100, 50 or 25% of field capacity) in glasshouses set at either low (15−25°C) or high (25−35°C) temperature regimes, over three growing cycles. Our aim was to explore whether differences in leaf water potential (LWP) and carbon assimilation rates could be reliable indicators of the relative yield potential and forage quality of the two cultivars in environments prone to water and heat stresses. At the low soil-water supply of 25% and low temperature, Bana had lower (more negative) LWP and relative water content (RWC) than Atherton, while at 50% and 100% soil-water supply, Bana had a higher tissue water status. Under the high temperature regime, Bana had consistently more positive LWP and RWC than Atherton, but the differences were not significant. The two cultivars had a similar CO2 assimilation rate (A) and there were no significant differences in the total dry matter yields over the three growing cycles. Water-use efficiency for above-ground biomass (kg ha–1 mm–1) was similar for both cultivars and was 28.5–35.1 under the low temperature regime and 16.9–22.9 under the high temperature regime. Neutral detergent fibre (NDF) was often higher for Bana at low water supply and low temperature than for Atherton, but the trend was reversed under the high temperature regime. Digestibility was generally improved under water-stressed conditions, and there was a positive correlation between NDF and both LWP and RWC measured at midday, but only under the low temperature regime. We conclude that LWP, RWC and A, alone or together, are inadequate for selecting cultivars for dry and hot environments, because cultivars may differ in other mechanistic responses to water stress and high temperatures.

In this paper, plant wilting is re-analysed and re-interpreted on the basis of previously published work. Wilting is considered only in terms of the stress caused by the matric suction of the soil water. Other factors that can induce wilting, such as salinity and plant pathogens, are not considered. It is found that there is confusion around the subject for two main reasons. First, it is usually assumed that the matric suction of the pore water that exists in soil samples when they are removed from pressure plate extractors is equal to the air pressure that was applied. Second (and this is a special case of the first reason), because the soil water content when most plants wilt is very close to that remaining in soil samples on pressure plates operating with an air pressure of 1.5 MPa, it is assumed that plants wilt at a pore water suction of 1.5 MPa. These assumptions are examined here, and it is shown that neither of them is true. Published results are used for the wilting condition. The recently described double-exponential (DE) equation for soil water retention is used for cases where the water is non-equilibrated because of hydraulic cut-off. The non-equilibrated condition is appropriate for plant roots because they, like pressure plate extractors, extract water from soil by immiscible displacement. The DE equation is used to illustrate the conditions under which plant wilting can be either a plant or a soil property. It is shown how this approach can be used to estimate the pore water suction at which plants would wilt because the soil is no longer able to supply water to their roots. It is demonstrated that the commonly used, but often erroneous, value for the wilting-point suction of h = 1.5 MPa is a consequence of the fact that this is the largest value of air pressure used in pressure cell extractors. It is therefore neither a plant nor a soil property, but is an artefact of the experimental procedure. The use of the DE equation for soil water retention shows that we know only that h ≤1.5 MPa, and that h can be as small as 0.2 or 0.3 MPa. Implications for estimation of plant water availability in soils, for plant breeding, and for soil microbial activity are discussed.

Field capacity (FC) and permanent wilting point (PWP) are two critical input parameters required in various biophysical models. There are limited published data on FC and PWP of dryland cropping soils across north-western Victoria. Direct measurements of FC and PWP are time-consuming and expensive. Reliable prediction of FC and PWP from their functional relationships with routinely measured soil properties can help to circumvent these constraints. This study provided measured data on FC using undisturbed samples and PWP as functions of geomorphological unit, soil type, and soil texture class for dryland cropping soils of north-western Victoria. We used a balanced, nested sampling strategy and developed functional relationships of FC and PWP with routinely measured soil properties using residual maximum likelihood based mixed-effects regression modelling. Using the data, we also tested the adequacy of nine published pedotransfer functions (PTFs) in predicting FC and PWP. Significant differences were observed among the three soil types and nine texture classes for most soil properties. FC and PWP were higher for Grey Vertosols (FC 43.7% vol, PWP 29.1% vol) than Hypercalcic Calcarosols (38.4%, 23.5%) and Red Sodosols (20.2%, 9.2%). Of the several functional relationships developed for prediction of FC and PWP, a quadratic single-predictor model based on dg (geometric mean particle size diameter) performed better than other models for both FC and PWP. It was nearly bias-free, with a root mean square error (RMSE) of 3.18% vol and an R2 of 93% for FC, and RMSE 3.47% vol and R2 89% for PWP. Another useful model for FC was a slightly biased, two-predictor quadratic model based on clay and silt, with RMSE 3.14% vol and R2 94%. For PWP, two other possibly useful, though slightly biased, models included a single-predictor quadratic model based on clay (RMSE 3.45% vol, R2 89%) and a three-predictor model based on clay, silt, and σg (geometric standard deviation of particle size diameter) (RMSE 3.27% vol, R2 90%). We observed a strong quadratic relationship of FC with PWP (RMSE 1.61% vol, R2 98%). This suggests the possibility to further improve the prediction of FC indirectly through PWP. These predictive models for FC and PWP, though developed for the dryland cropping soils of north-western Victoria, may be applicable to other regions with similar soil and climatic conditions. Some validation is desirable before these models are confidently applied in a new situation. Of the nine published PTFs, the multiple linear regression and artificial neural network based NTh5 for FC and NTh3 and CAM for PWP performed better on our data for the prediction of FC and PWP. The root mean square deviation of these PTFs, for both FC and PWP, was higher than the RMSE of our models. Our models are therefore likely to perform better under the dryland cropping soils of north-western Victoria than these PTFs. As a safeguard against arriving at optimistic inferences, we suggest that the modelling of functional relationships needs to account for the hierarchical structure of the sampling design using appropriate mixed effects regression models.

It is important to apply phosphorus (P) to the soil at the beginning of the crop growth cycle to provide essential P for early growth and to replace P exported in previous crops. With low rates of P added at sowing there may be sufficient P supply to grow crops to tillering, but in seasons of increased yield potential a top-up application of P may be required. Foliar P can be applied directly to the plant when required and in some cases have been shown to provide benefits for increasing P-use efficiency and the P concentration in grain. Wheat (Triticuum aestivum cv. Frame) was grown in two soils of marginal P status with soil moisture maintained at 80% of field capacity. Seven foliar P treatments labelled with 33P as a tracer were applied at Zadoks growth stage 39, at 1.65 kg P/ha with 120 L water/ha equivalent. Grain, chaff and shoots were harvested to measure yield and then digested to measure P concentrations and 33P activities. There was no crop response to top-up soil or foliar P on one soil, but on the other soil, foliar phosphoric acid plus adjuvant gave a 25% wheat grain yield response. The use of the tracing technique enabled measurement of the portioning of foliar P fertiliser between stem, chaff and grain. The most responsive treatment had the greatest amount of grain P uptake and the greatest partitioning of the foliar P fertiliser to grain.

Reducing soil compaction is now an important issue in agriculture due to intensive use of farm machinery in different farm operations. This experiment was designed to study the influence of combinations of external load and soil water on soil compaction. Four soil water levels were combined with four external loads as follows: soil water—air-dry, 50% of field capacity, field capacity, and saturation; external load using different-sized tractors—no load (0 kg), small tractor (2638 kg), medium tractor (3912 kg), and large tractor (6964 kg). Soil bulk density, soil strength, and soil water infiltration rate were measured at 0–100, 100–200, and 200–300 mm soil depths. The 16 treatments were set up in a randomised block design with three replications. Combined increases in soil water and external load increased soil compaction, as indicated by increasing soil bulk density and soil strength and decreasing soil water infiltration rate. There was no significant interaction between soil water and external load for bulk density at all soil depths, but the interaction was significant for soil strength and infiltration rates at all soil depths. The ratio between the weight of the external load and the surface area of contact between the external load and the ground was important in determining the degree of surface soil compaction. Least compaction was produced by the medium tractor because it had the highest tyre/ground surface area contact. In general, the effects of soil water and external load on increasing soil bulk density and soil strength were greater in the topsoil than the subsoil.

Nitrous oxide (N2O) from agricultural soils is a major source of greenhouse gas emissions in New Zealand. Nitrification inhibitors are seen as a potential technology to reduce these N2O emissions from agricultural soils. In previous studies on the effect of dicyandiamide (DCD) on N2O emissions from animal excreta, DCD was directly applied to urine. However, farmers apply DCD to grazed pastures shortly before or after grazing rather than applying it specifically to the urine patches. Accordingly, the objectives of this study were: (1) to test, using chamber measurements, whether the same level of N2O reduction is achieved under grazed conditions where excretal N is non-uniformly deposited, (2) to apply the process-based NZ-DNDC model to simulate the effect of DCD on emission reductions, and (3) to perform a sensitivity analysis on the NZ-DNDC model to investigate how uncertainties in the input parameters affect the modelled N2O emissions. Two circular 1260-m2 treatment plots were grazed simultaneously for 5 h, by 20 cattle on each plot. The following day, DCD was applied in 800 L of water to one of the plots at 10 kg/ha and N2O emissions were measured periodically for 20 days. The cumulative N2O emissions were 220 ± 90 and 110 ± 20 g N2O-N/ha for the untreated and DCD-treated plots, respectively (based on the arithmetic mean and standard error of the chambers). This suggests a reduction in N2O emission from DCD application of ~50 ± 40% from a single grazing event. However, this result should be treated with caution because the possibility of sampling error due to the chamber distribution cannot be excluded. NZ-DNDC simulated N2O emissions of 169 and 68 g N2O-N/ha for the untreated and DCD-treated areas, respectively, corresponding to a reduction of 60% in N2O emissions from DCD application. This level of reduction is consistent with that found in experiments with individual urine patches. N2O emissions found through use of NZ-DNDC were sensitive to uncertainties in the input parameters. The combined effect of varying the initial soil NO3– and NH4+, soil moisture, soil organic carbon, bulk density, clay content, pH, and water-filled pore-space at field capacity inputs within plausible ranges was to change the simulated N2O emissions by –87% to +150%.

Many studies on salinity stress assume that responses in hydroponics mimic those in soil. However, interactions between the soil solution and the soil matrix can affect responses to salinity stress. This study compared responses to salinity in hydroponics and soil, using two varieties of barley (Hordeum vulgare L.). The responses to salinity caused by high concentrations of Na+ and Cl– were compared to assess any consistent differences between hydroponics and soil associated with a cation and an anion that contribute to salinity stress. Concentrated nutrient solutions were also used to assess the effects of osmotic stress. The effects of salinity differed between the hydroponic and soil systems. Differences between barley cultivars in growth, tissue moisture content and ionic composition were not apparent in hydroponics, whereas significant differences occurred in soil. Growth reductions were greater under hydroponics than in soil at similar electrical conductivity values, and the uptake of Na+ and Cl– was also greater. The relative importance of ion exclusion and osmotic stress varied. In soil, ion exclusion tended to be more important at low to moderate levels of stress (EC at field capacity up to 10 dSm–1) but osmotic stress became more important at higher stress levels. High external concentrations of Cl– had similar adverse effects as high concentrations of Na+, suggesting that Cl– toxicity may reduce growth. Fundamental differences in salinity responses appeared between soil and solution culture, and the importance of the different mechanisms of damage varies according to the severity and duration of the salt stress. Refereed/Peer-reviewed

Pot experiments were conducted using a sandy loam soil and various electrolyte solutions such as NaCl, CaCl2, Na2SO4, and Hoagland nutrient solution containing all macro- and micro-nutrient elements in appropriate proportions, inducing different electrical conductivity (EC) levels of the soil solution during the growth of Krichauff wheat while the water content in the pot soils was maintained at field capacity. The resulting differences in dry matter production after 40 days of growth clearly indicated the continuous operation of osmotic effect as the EC of the soil solution increased from 0.7 to 41.0 dS/m. However, the osmotic effect became dominant and severely restricted plant growth when the soil solution EC increased above a ‘threshold value’, which was 25 dS/m, corresponding to an osmotic pressure of 900 kPa, in this experiment. Below this EC value, particularly at low EC values, ionic effects due to Na+, Ca2+, SO42–, and Cl– were also evident, but it could not be concluded whether these effects were due to toxicity or ion imbalance. The osmotic effect at EC values above the threshold resulted in greatly reduced water uptake from pot soils, the unused water being in the range 89–96% of the field capacity of the soil. Water use efficiency is a major factor in profitable and sustainable dryland agriculture. Both soil management and selection and breeding of salt-tolerant plants should concentrate on ensuring that the threshold EC value for severe osmotic effects is not reached under field conditions.

A pot and a field experiment were conducted to assess whether seeding density in winter wheat affects grain yield and water-use efficiency when combined with root pruning. Both experiments compared four treatments, namely (i) low (normal) plant density with no root pruning; (ii) low plant density with root pruning; (iii) high plant density (25% higher than low density) with no root pruning; and (iv) high plant density with root pruning. Roots to a depth of 25 cm were cut back to keep their length to 13 cm and to limit their lateral spread to 13 cm from the plant. In the pot experiment, two water regimes were employed from stem elongation: (i) plants maintained at 85% field capacity, and (ii) plants maintained at 55% field capacity by regular watering. Low rainfall in spring at the terminal stage of plant growth served as natural water stress in the field experiment. In the field, the higher plant density induced higher root biomass at all sample depths at anthesis. Root pruning significantly decreased the root biomass in the upper soil layer (0–40 cm) and increased the root biomass in the deep soil layer (80–120 cm). When water was limited, increasing the seeding density by 25% reduced the grain yield, but with adequate water increasing the seeding density increased the grain yield. Root pruning increased the grain yield, but there was no interaction between seeding density and root pruning on grain yield in either the pots or field. Root pruning reduced water use between stem elongation and anthesis which led to more available soil water in the field between anthesis and maturity, and increased the rate of flag leaf photosynthesis at anthesis, whereas the reverse was true of increasing seeding density. Measurements of chlorophyll fluorescence suggested that initially root pruning induced a stress in the plants, but that the pruned plants rapidly recovered so that by anthesis and during grain filling the level of stress was reduced. Increasing the seeding density increased the number of spikes (fertile tillers), but decreased the grain yield per spike and had no effect on the thousand-kernel weight. In contrast, root pruning reduced the number of spikes in both the field and pots, but increased the grain yield per spike and thousand-kernel weight. Under our experimental conditions, restricting the root size by root pruning increased the yield and water-use efficiency of winter wheat in water-limited environments.

Seed persistence of Gymnocoronis spilanthoides (D.Don) DC.; Asteraceae (Senegal tea), a serious weed of freshwater habitats, was examined in relation to burial status and different soil moisture regimes over a 3-year period. Seeds were found to be highly persistent, especially when buried. At the end of the experiment, 42.0%, 27.3% and 61.4% of buried seeds were viable following maintenance at field capacity, water logged and fluctuating (cycles of 1week at field capacity followed by 3weeks’ drying down) soil moisture conditions, respectively. Comparable viability values for surface-situated seeds were ~3% over all soil moisture regimes. Predicted times to 1% viability are 16.2 years for buried seed and 3.8 years for surface-situated seed. Persistence was attributed primarily to the absence of light, a near-obligate requirement for germination in this species, although secondary dormancy was induced in some seeds. Previous work has demonstrated low fecundity in field populations of G. spilanthoides, which suggests that soil seed banks may not be particularly large. However, high levels of seed persistence, combined with ostensibly effective dispersal mechanisms, indicate that this weed may prove a difficult target for regional or state-wide eradication.

Spatial variability in grain yield can arise from variation in many different soil and terrain properties. Identification of important sources of variation that bear significant relationship with grain yield can help achieve more effective site-specific management. This study had three aims: (i) a geostatistical description/modelling of the paddock-level spatial structure in variability of plant-available water capacity (PAWC) and related soil properties, (ii) to determine optimal number of management zones in the paddock, and (iii) to assess if the variability in PAWC and related soil properties is significantly associated with the variability in grain yield across the management zones. Particle size distribution, bulk density (BD), field capacity (FC), permanent wilting point (PWP), and soil water content (SWC) at sowing were measured at 4 soil depths (to 0.60 m) at 50 representative spatial sampling locations across a paddock near Birchip (Victoria). PAWC and plant-available water at sowing (PAWs) were derived from these data. Moderate to strong spatial dependence across the paddock was observed. The magnitude of the structural variation and of range varied widely across different soil properties and depths. The south-east edge and the central areas of the paddock had higher clay content, FC, PWP, PAWC, and lower PAWs. The paddock was divided into 6 potential management zones using combined header yield and normalised difference vegetation index (NDVI). The adequacy of zoning was evaluated using relative variability (RV) of header yield and soil properties. The mean RV for 3 zones differed little from that of 6 management zones for header yield and for each measured soil property, indicating division of the paddock into 3 zones to be adequate. The results from residual maximum likelihood (ReML) analysis showed that low yield zones had significantly higher clay content, FC, PWP, SWC, and PAWC and significantly lower PAWs than both medium and high yield zones. The mean FC, PWP, and PAWC in the low yield zones were, respectively, 25%, 26%, and 28% higher, and PAWs 36% lower than their corresponding values in the high yield zones. Linear regression analysis indicated that 59–96% of the observed variation in grain yield across management zones could be explained by variation in PWP. The practical implications of these results are discussed.

Carbon and nitrogen mineralisation potential of mixed cotton (Gossypium hirsutum L.) and cowpea (Vigna unguiculata (L.) Walp) crop residues produced under intercropping, as well as a reddish-brown soil classified by FAO as Ferralic Cambisol previously under intercrops, were studied over a 10-week incubation period under controlled conditions (25°C and moisture content of 70% field capacity, 125 mm) in the laboratory. Treatments consisted of cotton residues (100 : 0), cowpea residues (0 : 100), and cotton–cowpea residues (50 : 50, 70 : 30, and 30 : 70). These ratios were based on yields obtained in different cotton–cowpea intercrop treatments from a field study. Cowpea residues (0 : 100) released the highest amount of mineral N of 36.4 mg/kg soil, and cotton residues (100 : 0) least, 19.2 mg/kg soil, while the other mixtures were in between. All treatments except for cowpea residues (0 : 100) and the 30 : 70 mixture showed immobilisation of soil N during the first 2 weeks of incubation. The trend for C mineralisation was similar to that of N, and cowpea residues (0 : 100) released the highest amount, 492 mg C/kg soil, while cotton residues (100 : 0) recorded the least, 315 mg C/kg soil. The C mineralisation patterns of cowpea residues (0 : 100) and 30 : 70 treatments were exponential and were well described by the equation: where CE is exponentially mineralisable C fraction, k is the rate constant, and t is time in days. The mineralisation patterns for other treatments were sigmoidal and were well described by the equation: where CS is sigmoidally mineralisable C fraction; t 0 is time in days required for complete mineralisation of CS , while k is rate constant. The amount of N released from soil previously under cotton–cowpea intercrops and sole crops was approximately one-third of the amount released when the residues were incorporated. The highest amount of N released (12.2 mg/kg soil) was from soil previously under sole cowpea, while soil from the 1 : 1 cotton–cowpea intercrop released 9.9 mg/kg soil and soil from sole cotton released 5.9 mg/kg soil. There was no significant effect (P > 0.05) of previous crop on C mineralisation patterns of the soil. Mixtures slow down N losses and increase nutrient use efficiency of legume residues, especially in the short-term. When cotton is grown as a sole crop, starter N to offset negative effects of initial N-immobilisation at the start of season is required. A better understanding of controlling parameters of decomposition can make it possible to predict C and N mineralisation patterns in mixtures. Reduced C mineralisation in cotton–cowpea mixtures may result in more C sequestration and, hence, SOM build-up and improved sustainability in the long term in intercropping systems.

In New Zealand, urine deposited by grazing animals represents the largest source of nitrogen (N) losses, as gaseous emissions of ammonia (NH₃) and nitrous oxide (N₂O), and leaching of nitrate (NO₃⁻).We determined the effect of dicyandiamide (DCD) on gaseous emissions from pasture with increasing rates of urine-N application, mineral N transformations and potential leaching of N using undisturbed soil cores of Manawatu sandy loam at field capacity. The treatments included four levels of urine-N applied at 0 (control), 14.4, 29.0 and 57.0 g N/m² with and without DCD at 2.5 g/m². Results showed a significant (P < 0.05) increase in NH₃ and N₂O-N emissions as urine application was increased. The addition of DCD to corresponding urine treatments reduced N₂O emissions by 33, 56 and 80%, respectively. The addition of DCD with urine to the intact soil cores at field capacity moisture content resulted in a significant increase in the soil ammonium-N (NH₄⁺-N) concentration but little change in NH₃ emissions. Addition of DCD to urine reduced potential NO₃⁻-N leaching by 60–65% but potential NH₄⁺-N leaching increased by 2–3.5 times. There was no difference in pasture dry matter production with and without DCD treatments. Refereed/Peer-reviewed

The Sanjiang Plain of north-east China is presently the second largest freshwater marsh in China. The drainage and use of marshes for agricultural fields occurred in the past 50 years, resulting in the increase in cultivated land from about 2.9 × 108 m2 in 1893 to 4.57 × 1010 m2 in 1994. Under human disturbance in the past half century, the environment in Sanjiang Plain has had significant change. We hypothesised that environmental factors such as soil moisture, soil temperature, and soil N levels affect the rates of soil organic C mineralisation and the nature of the controls on microbial CO2 production to change with depth through the soil profile in the freshwater marsh in the Sanjiang Plain. In a series of experiments, we measured the influence of soil temperature, soil water content, and nitrogen additions on soil microbial CO2 production rates. The results showed that Q10 values (the factor by which the CO2 production rate increases when the temperature is increased by 10°C) significantly increased with soil depth through the soil profile (P 0.80. The sensitivity of microbial CO2 production rate response to soil water content for surface soils (0–0.2 m) was slightly lower than for subsurface soils (0.2–0.6 m). The responses of actual soil respiration rates to nitrogen fertilisation were different for surface and subsurface soils. In the surface soils (0–0.2 m), the addition of N caused a slight decreased in respiration rates compared with the control, whereas, in the subsurface soils (0.2–0.6 m), the addition of N tended to increase microbial CO2 production rates, and the addition of 10 µg N/g soil treatment caused twice the increase in C mineralisation rates of the control. Our results suggested that the responses of microbial CO2 production to changes in soil moisture, soil temperature, and soil N levels varied with soil depth through the profile, and subsurface soil organic C was more sensitive to temperature increase and nitrogen inputs in the freshwater marsh of the Sanjiang Plain.

A pot trial was carried out to investigate the effect of biochar produced from greenwaste by pyrolysis on the yield of radish (Raphanus sativus var. Long Scarlet) and the soil quality of an Alfisol. Three rates of biochar (10, 50 and 100 t/ha) with and without additional nitrogen application (100 kg N/ha) were investigated. The soil used in the pot trial was a hardsetting Alfisol (Chromosol) (0–0.1 m) with a long history of cropping. In the absence of N fertiliser, application of biochar to the soil did not increase radish yield even at the highest rate of 100 t/ha. However, a significant biochar × nitrogen fertiliser interaction was observed, in that higher yield increases were observed with increasing rates of biochar application in the presence of N fertiliser, highlighting the role of biochar in improving N fertiliser use efficiency of the plant. For example, additional increase in DM of radish in the presence of N fertiliser varied from 95% in the nil biochar control to 266% in the 100 t/ha biochar-amended soils. A slight but significant reduction in dry matter production of radish was observed when biochar was applied at 10 t/ha but the cause is unclear and requires further investigation. Significant changes in soil quality including increases in pH, organic carbon, and exchangeable cations as well as reduction in tensile strength were observed at higher rates of biochar application (>50 t/ha). Particularly interesting are the improvements in soil physical properties of this hardsetting soil in terms of reduction in tensile strength and increases in field capacity.

We report on the relationship between growth, partitioning of shoot biomass and hydraulic development of Eucalyptus tereticornis Sm. grown in glasshouses for six months. Close coordination of stem vascular capacity and shoot architecture is vital for survival of eucalypts, especially as developing trees are increasingly subjected to spasmodic droughts and rising atmospheric CO2 levels. Trees were exposed to constant soil moisture deficits in 45 L pots (30–50% below field capacity), while atmospheric CO2 was raised to 700 μL CO2 L–1 in matched glasshouses using a hierarchical, multi-factorial design. Enrichment with CO2 stimulated shoot growth rates for 12–15 weeks in well-watered trees but after six months of CO2 enrichment, shoot biomasses were not significantly heavier (30% stimulation) in ambient conditions. By contrast, constant drought arrested shoot growth after 20 weeks under ambient conditions, whereas elevated CO2 sustained growth in drought and ultimately doubled the shoot biomass relative to ambient conditions. These growth responses were achieved through an enhancement of lateral branching up to 8-fold due to CO2 enrichment. In spite of larger transpiring canopies, CO2 enrichment also improved the daytime water status of leaves of droughted trees. Stem xylem development was highly regulated, with vessels per unit area and cross sectional area of xylem vessels in stems correlated inversely across all treatments. Furthermore, vessel numbers related to the numbers of leaves on lateral branches, broadly supporting predictions arising from Pipe Model Theory that the area of conducting tissue should correlate with leaf area. Diminished water use of trees in drought coincided with a population of narrower xylem vessels, constraining hydraulic capacity of stems. Commensurate with the positive effects of elevated CO2 on growth, development and leaf water relations of droughted trees, the capacity for long-distance water transport also increased.

The amount of water that can be stored in soil and evaporated or actively used by plants is a key parameter in hydrologic models and is important for crop and pasture production. Often, the active soil moisture store is estimated from laboratory measurements of soil properties. An alternative approach, described in this paper, is to estimate the extractable soil moisture capacity from direct measurements of soil moisture content in the field. A time series of soil moisture values, over the depth of the soil, shows the actual changes in water content. The difference between the wettest and driest profiles is an estimate of the extractable soil moisture storage. We have gathered data on extractable soil water capacity for 180 locations over Australia and have compared our values with published results from the Atlas of Australian Soils (AAS), derived from profile descriptions and pedo-transfer functions. Our results show that data from the AAS provide a useful lower bound for measured extractable soil moisture storage, but of the sites examined, 42% had values >2 times those in the AAS. In part, this was because total soil depths were underestimated in the AAS results compared with the active depths from the measured data. Active depths are strongly related to vegetation type.

Red-brown earths (Red Sodosols and Red Chromosols) are the dominant soil type used for irrigated forage production in northern Victoria. However, these soils have dense, clay-textured subsoils that can limit productivity. Soil modification may reduce these limitations through improving subsoil structure. In a field experiment on a Red Chromosol near Kyabram, we compared 2 systems of soil modification involving deep ripping and gypsum application (with and without subsurface drainage) with an unmodified control. Two irrigation frequencies were imposed. This paper reports on the site establishment and the soil physical responses to soil modification. Later papers detail the forage yield responses and plant–soil–water relations. Initially, both soil modification treatments improved the physical condition of the subsoil. For example, the bulk density of the modified and the drained subsoils was reduced to about 1.48 Mg/m3, compared with 1.71 Mg/m3 in the control. Soil strength was reduced in the modified and drained treatments between depths of 0.10–0.40 m at most soil water contents. In the subsoil, the modified and drained treatments had smaller soil aggregates with about 60% by weight being less than 20 mm diameter compared with 39% from the control treatment. Subsoil hydraulic conductivity, at 10 mm water tension, was 12 mm/h in the control, 33 mm/h in the modified treatment and 71 mm/h in the drained treatment when measured 1 year after the treatments were imposed. These improvements in soil physical properties generally persisted for the 2 years of measurements.

The moisture characteristics and related pore size distributions of Thai Oxisols were determined for 11 representative pedons. These soils are Kandiustox and Kandiudox located in the North-east Plateau, South-east Coast, and Peninsular Thailand. They are generally acidic (pH 5–6), clayey, have low cation exchange capacity (5–15 cmolc/kg) and have low bulk densities (0.77–1.36 Mg/m3). The microstructures of these soils are mostly granular with compound packing 10–1500 μm voids between aggregates. Water retention curves for all soils are similar with amounts of water retained at 33 kPa (field capacity) ranging from 22 to 43 (%weight) and 1500 kPa (permanent wilting point) ranging from 17 to 34%. Water available to plants is 3–12%. There is a strongly bimodal pore size distribution with the modal macropore and micropore diameters calculated from the soil moisture retention characteristic curves being about 100 μm and 0.02 μm. The pore size distribution determined by N2-BET method indicates a modal micropore of about 0.01 μm. The total volume of pores >5 μm estimated by image analysis of scanning electron micrographs ranges from 20 to 50% with most of the variation in porosity being due to large differences in macropore (>75 μm) volume.

Adoption of conservation tillage practices on Red Ferrosol soils in the inland Burnett area of south-east Queensland has been shown to reduce runoff and subsequent soil erosion. However, improved infiltration resulting from these measures has not improved crop performance and there are suggestions of increased loss of soil water via deep drainage. This paper reports data monitoring soil water under real and artificial rainfall events in commercial fields and long-term tillage experiments, and uses the data to explore the rate and mechanisms of deep drainage in this soil type. Soils were characterised by large drainable porosities (≥0.10 m3/m3) in all parts of the profile to depths of 1.50 m, with drainable porosity similar to available water content (AWC) at 0.25 and 0.75 m, but >60% higher than AWC at 1.50 m. Hydraulic conductivity immediately below the tilled layer in both continuously cropped soils and those after a ley pasture phase was shown to decline with increasing soil moisture content, although the rate of decline was much greater in continuously cropped soil. At moisture contents approaching the drained upper limit (pore water pressure = –100 cm H2O), estimates of saturated hydraulic conductivity after a ley pasture were 3–5 times greater than in continuously cropped soil, suggesting much greater rates of deep drainage in the former when soils are moist. Hydraulic tensiometers and fringe capacitance sensors monitored during real and artificial rainfall events showed evidence of soils approaching saturation in the surface layers (top 0.30–0.40 m), but there was no evidence of soil moistures exceeding the drained upper limit (i.e. pore water pressures ≤ –100 cm H2O) in deeper layers. Recovery of applied soil water within the top 1.00–1.20 m of the profile during or immediately after rainfall events declined as the starting profile moisture content increased. These effects were consistent with very rapid rates of internal drainage. Sensors deeper in the profile were unable to detect this drainage due to either non-uniformity of conducting macropores (ie. bypass flow) or unsaturated conductivities in deeper layers that far exceed the saturated hydraulic conductivity of the infiltration throttle at the bottom of the cultivated layer. Large increases in unsaturated hydraulic conductivities are likely with only small increases in water content above the drained upper limit. Further studies with drainage lysimeters and large banks of hydraulic tensiometers are planned to quantify drainage risk in these soil types.

The effect of different irrigation strategies on turnip forage crop growth rates, dry matter (DM) yield, water use efficiency (WUE), changes in soil volumetric water content, nutritive characteristics and mineral content was determined on different soil types at different sites (site 1 and 2) over 2 years. Treatments were: (A) a dryland control; (B) fully watered to soil field capacity each week; (C) 75% of full watering; (D) 50% of full watering; (E) 25% of full watering; (F) a single watering to soil field capacity or to a maximum of 50 mm between weeks 0–6; (G) a single watering between weeks 6–8; (H) a single watering between weeks 8–10; and (I) a single watering between weeks 10–12 after sowing. In addition, each irrigation treatment received either 0 or 50 kg N/ha applied 5 weeks after sowing. Responses to applied irrigation water were different at each site and also within one year. At site 1, responses to irrigation were adversely affected by insect damage and delayed sowing, particularly in year 1. However, there were significant increases in DM yield to weekly irrigation regimes in both years, with responses greater in year 2, and responses in both years were greater where nitrogen was applied. At site 2, there were significant responses to weekly irrigation regimes in year 1 with DM yields from fully irrigated plots almost double that of the dryland treatment. In year 2, DM yields from all treatments were similar and it is proposed that lower summer temperatures may have contributed to the improved DM yield observed with the dryland treatment. In both years, at site 2, there were generally higher DM yields with nitrogen application irrespective of irrigation regime. Turnip metabolisable energy values were consistently above 11.5 and 13 MJ/kg DM for leaves and roots respectively, with crude protein contents for leaves ranging from 11 to 20% and 13 to 24% and roots from 6 to 14% and 9 to 17% at sites 1 and 2, respectively. Water use efficiencies varied according to irrigation treatment with higher efficiencies observed at site 2 in both years. In year 1 and 2, total WUE at site 1 varied from 5 to 11 kg DM/ha.mm while at site 2 the range was 20–48�kg�DM/ha.mm with higher values being observed in year 2. As with DM yields it is likely that the observed higher WUE in year 2 was due to lower summer temperatures. At site 2, the dryland treatments produced the highest efficiencies in both years. In contrast, WUE from applied irrigation water ranged from 0 to 35 kg DM/ha.mm at site�1 and from 0 to 23 kg DM/ha.mm at site 2. This study suggests that there is potential to economically irrigate turnips to provide additional DM of high nutritional value for lactating dairy cows, however, issues such as sowing dates, soil type, and insect damage will also influence final yields. In particular, summer temperatures influence both dryland growth potential and growth responses to irrigation. Also single irrigations during the growing period will not significantly increase DM yields over a crop grown under dryland conditions.

Dissolution of dry-milled basalt, dolerite, gneiss, and K-feldspar added to 23 soils has been related to milling time and soil properties. The rocks milled for 10, 60, and 120 min were mixed with 23 type of soils from south-western Australia at a rock/soil ratio of 1/100 (≈10 t/ha), wetted to 110% field capacity, then incubated at 20°C for 2 and 10 months. Measurements of cations extractable by 1 M CH3COONH4 at pH 7 indicate that substantial dissolution occurred in the soil and that milling increased dissolution. After 10 months of incubation, about 18% of Ca and Mg had dissolved from basalt and dolerite milled for 120 min and 40% of Na and K from gneiss and K-feldspar milled for 120 min. Some dissolution occurred with 1 h extraction of non-incubated rock–soil mixtures and these released elements are considered to be readily available plant nutrients. The silicate rocks had minor effects on soil pH and EC of soil-rock mixtures (i.e. increased pH by ≤0.5 unit and EC by ≤127 μS/cm in 1 : 5 water extracts). The large increases in silicate rock dissolution in soils due to milling indicate that milled basalt and dolerite may be used as Ca and Mg fertilisers, and K-feldspar as a K fertiliser. Further research is needed to identify soils and plants for which the application of the silicate rock fertilisers will be most beneficial.

Tropospheric methane (CH4) is oxidised by soil microbes called methanotrophs. We examined them in soil samples from a pristine Nothofagus forest located in New Zealand. Laboratory incubations indicated the presence of high-affinity methanotrophs that displayed Michaelis–Menton kinetics (Km = 8.4 µL/L where Km is the substrate concentration at half the maximal rate). When the soil was dried from its field capacity water content of 0.34 to 0.16 m3/m3, CH4 oxidation rate increased nearly 7-fold. The methanotrophs were thus metabolically poised for very high activity, but substrate availability was commonly limiting. When water content was held constant, CH4 oxidation rate nearly doubled as temperature increased from 5 to 12°C, a range found in the forest. By contrast, CH4 oxidation rate did not change much from 12 to 30°C, and it was zero at 35°C. When water content and temperature were held constant, the optimal soil pH for CH4 oxidation was 4.4, as found in the forest. Soil disturbance by nitrogen (N) and non-N salt amendment decreased CH4 oxidation rate, but this depended on the amendment species and concentration. The methanotrophs were adapted to native conditions and exhibited a great sensitivity to disturbance.

Carrot taproots are prone to radial longitudinal tissue fractures (splitting). The longitudinal alignment of the fractures is consistent with the tangential stress induced by radial growth in the annular cambium. In this study linear variable differential transformers were used to monitor the diurnal radial growth pattern of mature carrot taproots. The diurnal growth pattern was characterised by rapid expansion during the night (dark) period and small shrinkage during the light period. The magnitude of the daily shrinkage was positively correlated with both vapour pressure deficit and global radiation. A positive correlation between the rate of taproot expansion during the night period and global radiation level the preceding day was also recorded. Water stress reduced the taproot night time expansion rate, but the taproot of water stressed plants expanded rapidly when watered to field capacity. Partial defoliation of plants at midday resulted in immediate expansion of the taproot, however, the daily growth rates of the partially defoliated plants was less than untreated control plants over the following 3 days. It was concluded that the short-term changes in taproot diameter could be used to infer changes in tangential stresses and therefore taproot splitting propensity.

Pools of soil selenium (Se) as influenced by moisture regimes were investigated in some normal and seleniferous (which produce vegetation containing >5 mg Se/kg—the maximum permissible level for animal consumption) soils of India. Soil samples were equilibrated with 75 Se by subjecting to alternate wetting and drying cycles and incubated at field capacity and submerged moisture regimes. Each soil sample was subjected to either single extraction with 0.25 M KCl, 0.1 M KH2PO4, and 4 M HCl in a sequence or 7 extractions with KCl followed by 7 extractions with KH2PO4 and 2 with HCl. Amount of 75 Se extracted from different soils incubated at field capacity through single extraction with 0.25 M KCl varied from 8.4 to 30.5% of applied 75 Se for alkaline and 2.6 to 10.4% for acidic soils. Among alkaline soils, a greater amount of 75 Se was extracted from highly calcareous non-seleniferous soils than seleniferous soils. The amount of selenium extracted through 7 sequential extractions with 0.25 M KCl was 1.5-7.0 times greater than that extracted through single extraction. A significant coefficient of correlation between 75 Se extracted through repeated extractions with 0.25 M KCl and pH of the soils (r = 0.93, P ≤ 0.01) suggested greater availability of Se in alkaline than acidic soils. Specifically sorbed soil Se extracted with 0.1 M KH2PO4 through 7 sequential extractions ranged from 15.3 to 24.6% for alkaline and 24.4 to 40.1% for acidic soils. The amount of 75 Se desorbed through multiple extractions with 4 M HCl was negatively correlated with pH (r = -0.95, P ≤ 0.01) and electrical conductivity (r = -0.85, P ≤ 0.05) of the soils. After subjecting to single extraction, residual 75 Se left in soils incubated at field capacity moisture varied from 11.7 to 59.7%. It was negatively correlated with pH (r = -0.85, P ≤ 0.05) and CaCO3 (r = -0.79, P ≤ 0.10) and positively correlated with ammonium oxalate extractable iron content (r = 0.76, P ≤ 0.10) of soils. Compared with the single extraction procedure, only a small amount (9-36%) of 75 Se was left as residual 75 Se after multiple extractions. Relatively less 75 Se was released when the alkaline or acidic soils incubated under submergence were subjected to single or multiple extraction procedures. The multiple extraction procedure could better assess different soil Se pools than the single extraction procedure. At field capacity moisture, large amounts of Se occur in easily available forms. Under submerged conditions, substantial amounts of Se are maintained in the soil solution when Se is removed from the solution through plant uptake or leaching. SR03 S. Kn i Poo ls u ndi

Soil pH affects N2O production mechanisms. The ratio of N2O to N2 may decrease with increasing soil pH during denitrification. Two laboratory experiments were performed to examine the effect of liming on N2O emissions following synthetic urine applications over 42 and 60 days. A silt loam soil at field capacity (water-filled pore space of 57% after treatment application) was adjusted with Ca(OH)2 to produce soils ranging from pH 4.7 to 7.7. The first experiment employed 4 treatments: a control, KNO3 (500 kg N/ha), and synthetic urine at 500 kg N/ha and 1000 kg N/ha. A second experiment used 15N labelled urea in synthetic urine at 500 kg N/ha. The main effect of lime was to promote nitrification, which markedly affected N2O fluxes. After 60 days, the 500 kg N/ha synthetic urine treatment limed to pH 6.1 produced more N2O (0.82% of N applied) than any other soil pH. No optimum soil pH was found for the synthetic urine treatment at 1000 kg N/ha with nitrification incomplete after 60 days. N2O production via nitrifiers dominated the N2O production pathway with large residual NO3– pools. Denitrification was not enhanced since no 15N labelled N2 was detected. However, before any final conclusions can be drawn about the efficacy of liming as a mitigation tool it is vital that the effect of liming on possible denitrification mechanisms and products also be assessed, following nitrification and formation of a nitrate pool. Application of synthetic urine also initiated a priming effect with more carbon evolved as CO2 than was applied.

Soils at a Long Term Ecological Research site near Lake Hoare in Taylor Valley, Antarctica, were investigated during November/December 1999. The soils alongside 6 experimental plots at the research site were described, repeatedly sampled over a 17-day period, and the gravimetric water content, particle size, and conductivity determined daily. At one nearby location, the soil water content was repeatedly measured after a plot irrigation, while at another, the water content of soil adjacent to a snow patch was repeatedly measured to determine the rate of water loss during thawing of snow. Soils at 2 sites at higher elevations outside the research area were also examined for comparison.The soils at the experimental plots were generally similar but differed in stoniness, the presence of occasional silty layers, and the depth to ice-cemented ground. Water contents (gravimetric) of surface horizons were

We report the results from a field experiment in which we examined the spatial and temporal patterns of water uptake by a mature apple tree (Malus domestica Borkh., 'Splendour') in an orchard. Time domain reflectometry was used to measure changes in the soil's volumetric water content, and heat-pulse was used to monitor locally the rates of sap flow in the trunk and roots of the tree. The tree's distribution of root-length density and supporting data to characterise the soil's hydraulic properties were determined for the purpose of modelling soil water movement in the root-zone under an apple tree. Experimental data are compared against the output from a numerical model of the soil water balance that uses Richards' equation for water flow, and uses a distributed macroscopic sink term for root uptake. In general, there was a very good agreement between the measured and modelled results. The apple trees consumed some 70 L of water per day during the middle of summer. The daily water use declined to about 20 L per day with the onset of autumn, coinciding with a reduced evaporative demand and an increasing number of rain days. Water movement in the root-zone soil was dominated by the water uptake via surface roots. Large changes in soil water content were also associated with each irrigation event. Our experimental data support the contention that more frequent irrigation in smaller doses will result in less water percolating through the root-zone. Such an irrigation strategy should make more efficient use of water by minimising the leaching losses. It will also be helpful for environmental protection by reducing the percolation losses of water and solute beyond the grasp of the roots.