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Studies across multiple soils find increasing pH decreases water repellency. In this study, water repellency and a range of other soil physical properties of bulk soils, aggregates and intact specimens were measured on a long-term pH field experiment on a single sandy loam soil under a ley-arable crop rotation, with soil pH adjustments occurring annually by adding FeSO4 or CaCO3, to lower or raise the pH, respectively. Crop impacts were investigated by comparing 3rd year grass-white clover to spring oats, at the beginning (May) and end (September) of the growing season to allow soil structure comparisons. As in previous research, increased CO2 microbial respiration (p 55 years of chemical additions to amend soil pH.

Alternate wetting and drying (AWD) irrigation can save large amounts of water in rice cultivation. By repeatedly wetting and drying the soil under AWD, accentuated pore structure of the rhizosphere compared to flooded rice may occur. This could affect root growth and resource capture, but to date the physical structure and behaviour of the rhizosphere of rice under AWD has not been explored. In a controlled glasshouse experiment, two different textured soils were used in split rhizotrunks to separate a root‐zone from bulk soil using mesh. To mimic a paddy field, the top of the rhizotrunk was filled with puddled soil and below the puddled layer there was a sieved soil layer. Root‐zone physical properties were measured using a combination of high resolution X‐ray CT imaging (pore structure), a miniaturised infiltrometer (hydrological) and a small indenter (mechanical). Soil under AWD irrigation had 46% greater macroporosity and 20% more pore connectivity compared to continuous flooding (CF). Compared to the bulk soil, root‐zone soil under AWD or CF had greater macroporosity, water sorptivity and mechanical hardness. In the root‐zone, AWD compared to CF increased the rate of water absorption by around 36%, but did not affect mechanical hardness. Our results suggest AWD interacting with rice roots could promote more effective water transmission through a more stable, larger and better‐connected pore system. The results of this study also suggest that soil physical changes by AWD could improve the utilization of resources in a rice production system. [ABSTRACT FROM AUTHOR]

The interface between plants' roots and soil is strongly affected by rhizodeposits, especially mucilage, that change mechanical and hydrological behaviour. In addition to impacts to aggregation, water capture and root penetration, rhizodeposits may also affect the pull‐out resistance of plant roots. Due to the complex architecture of plant roots and an inability to restrict rhizodeposit production, this study used a simplified system of wooden skewers to simulate roots and chia seed mucilage as a model to simulate rhizodeposit compounds. Pull‐out tests were then carried out to measure the impacts of mucilage, and one (WD1) or two (WD2) cycles of wetting and drying of soils. Using a mechanical test frame, the maximum pull‐out resistance (Fmax) and pull‐out displacement (dL) were recorded, allowing for pull‐out energy (E), average pull‐out force (F¯$$ \overline{F} $$) and bond strength (τmax) to be calculated. The results showed that all pull‐out parameters of the samples with added rhizodeposit compounds tended to decrease between WD1 and WD2, but they were still significantly greater than without the added mucilage. The model rhizodeposit increased all pull‐out parameters by a minimum of 30%. With an additional wet–dry cycle, the mucilage tended to cause a decline in pull‐out parameters relative to a single wet‐dry cycle. This suggests mucilages could enhance the mechanical resistance of roots to pull‐out, but resistance decreases over time with cycles of wetting and drying. To conclude, an important role of mucilage is pull‐out resistance, which has relevance to plant anchorage and root reinforcement of soils. [ABSTRACT FROM AUTHOR]

Subtropical regions have clay-rich, weathered soils, and long dry periods followed by intense rainfall that produces large fluctuations in soil water content (SWC) and hydrological behavior. This complicates predictions of spatio-temporal dynamics, as datasets are typically collected at too coarse resolution and observations often represent a duration that is too short to capture temporal stability. The aim of the present study was to gain further insights into the role of temporal sampling scale on the observed temporal stability features of SWC order to aid the design of optimal SWC sampling strategies. This focused on both sampling frequency and total monitoring duration, as previous analyses have not considered both of these sampling aspects simultaneously. We collected relatively high resolution data of SWC (fortnightly over 3.5 years) for various soil depths and under contrasting crops (peanuts and citrus) at the red soil region of southeast China. The dataset was split into a three-year training period and a six-month evaluation period. Altogether 13 sampling frequencies (intervals ranging from 15 to 240 days) and eight monitoring duration periods (between three and 36 months) were derived from the training period to identify temporal stability features and the most time stable location (MTSL). The prediction accuracies of these MTSLs were tested using the independent evaluation data. Results showed that vegetation type did affect the spatio-temporal patterns of SWC, whereby the citrus site exhibited a stronger temporal variation and weaker temporal stability than the peanut site. However, the effects of both sampling frequency and observation duration were more pronounced, irrespective of the role of vegetation type or soil depth. With increasing sampling interval or decreasing monitoring duration, temporal stability of SWC was generally overestimated; by less than 10% when sampling interval increased from every 15 to 240 days and by up to 40% with duration decreasing from 36 to 3 months. Our results suggest that sampling strategies and trade-offs between sampling interval and duration should focus on capturing the main variability in hydro-climatological conditions. For subtropical conditions, we found that sampling once every 45 days over 24 months to be the minimum sampling strategy to ensure errors in SWC temporal stability of less than 10%.

The extent (determined by the repellency indices RI and RIc) and persistence (determined by the water drop penetration time, WDPT) of soil water repellency (SWR) induced by pines were assessed in vastly different geographic regions. The actual SWR characteristics were estimated in situ in clay loam soil at Ciavolo, Italy (CiF), sandy soil at Culbin, United Kingdom (CuF), silty clay soil at Javea, Spain (JaF), and sandy soil at Sekule, Slovakia (SeF). For Culbin soil, the potential SWR characteristics were also determined after oven-drying at 60°C (CuD). For two of the three pine species considered, strong (Pinus pinaster at CiF) and severe (Pinus sylvestris at CuD and SeF) SWR conditions were observed. Pinus halepensis trees induced slight SWR at JaF site. RI and RIc increased in the order: JaF < CuF < CiF < CuD < SeF, reflecting nearly the same order of WDPT increase. A lognormal distribution fitted well to histograms of RIc data from CuF and JaF, whereas CiF, CuD and SeF had multimodal distributions. RI correlated closely with WDPT, which was used to develop a classification of RI that showed a robust statistical agreement with WDPT classification according to three different versions of Kappa coefficient.

In order to improve the sustainability of agriculture it is imperative that the P-use efficiency of temperate cereal crops be improved. This can be achieved both by agronomic and genetic approaches. While many studies have demonstrated genotypic variation in P-use efficiency in a number of cereal species the robustness of this genetic variation with variation in environment is rarely considered. In this paper we describe an experiment in which we compare the P-nutrition of winter and spring barley genotypes grown in a field trial with contrasting cultivation treatments (conventional vs. minimum tillage) which have been developed over a number of years. We demonstrate that while there is significant variation between genotypes in their P nutrition that this variation is not comparable between cultivation treatments and only one winter barley genotype (cv. Gleam) has beneficial P-use efficiency traits in both cultivation systems. These data suggest that it may be possible to identify a genetic component to variation in P nutrition in barley but that a large interaction with environmental variables may limit the usefulness of any genes or markers discovered for improving P-use efficiency to the conditions under which the screening was performed.

We developed an automated miniature constant-head tension infiltrometer that measures very small infiltration rates at millimetre resolution with minimal demands on the operator. The infiltrometer is made of 2.9 mm internal radius glass tube, with an integrated bubbling tower to maintain constant negative head and a porous mesh tip to avoid air-entry. In the bubbling tower, bubble formation and release changes the electrical resistance between two electrodes at the air-inlet. Tests were conducted on repacked sieved sands, sandy loam soil and clay loam soil, packed to a soil bulk density ρd of 1200 kg m-3 or 1400 kg m-3 and tested either air-dried or at a water potential ψ of -50 kPa. The change in water volume in the infiltrometer had a linear relationship with the number of bubbles, allowing bubble rate to be converted to infiltration rate. Sorptivity measured with the infiltrometer was similar between replicates and showed expected differences from soil texture and ρd, varying from 0.15 ± 0.01 (s.e.) mm s-1/2 for 1400 kg m-3 clay loam at ψ = -50 kPa to 0.65 ± 0.06 mm s-1/2 for 1200 kg m-3 air dry sandy loam soil. An array of infiltrometers is currently being developed so many measurements can be taken simultaneously.