Tillage effects on soil hydraulic properties in space and time: State of the science

Soil tillage practices can affect soil hydraulic properties and processes dynamically in space and time with consequent and coupled effects on chemical movement and plant growth. This literature review addresses the quantitative effects of soil tillage and associated management (e.g., crop residues) on the temporal and spatial variability of soil hydraulic properties. Our review includes incidental management effects, such as soil compaction, and natural sources of variability, such as topography. Despite limited research on space–time predictions, many studies have addressed management effects on soil hydraulic properties and processes relevant to improved understanding of the sources of variability and their interactions in space and time. Whether examined explicitly or implicitly, the literature includes studies of interactions between treatments, such as tillage and residue management. No-tillage (NT) treatments have been compared with various tillage practices under a range of conditions with mixed results. The trend, if any, is for NT to increase macropore connectivity while generating inconsistent responses in total porosity and soil bulk density compared with conventional tillage practices. This corresponds to a general increase in ponded or near-zero tension infiltration rates and saturated hydraulic conductivities. Similarly, controlled equipment traffic may have significant effects on soil compaction and related hydraulic properties on some soils, but on others, landscape and temporal variability overwhelm wheel-track effects. Spatial and temporal variability often overshadows specific management effects, and several authors have recognized this in their analyses and interpretations. Differences in temporal variability depend on spatial locations between rows, within fields at different landscape positions, and between sites with different climates and dominant soil types. Most tillage practices have pronounced effects on soil hydraulic properties immediately following tillage application, but these effects can diminish rapidly. Long-term effects on the order of a decade or more can appear less pronounced and are sometimes impossible to distinguish from natural and unaccounted management-induced variability. New standards for experimental classification are essential for isolating and subsequently generalizing space–time responses. Accordingly, enhanced methods of field measurement and data collection combined with explicit spatio-temporal modeling and parameter estimation should provide quantitative predictions of soil hydraulic behavior due to tillage and related agricultural management.     

Spurious hypercreatininemia: 28 neonatal foals (2000–2008)

Objectives – To (1) determine the occurrence of spurious hypercreatininemia in a population of hospitalized foals <2 days old, (2) assess the resolution of the hypercreatininemia, and (3) determine its association with survival in these foals. Design – Retrospective case series. Setting – 2 Referral hospitals. Animals – Foals <2 days old with an admission creatinine >442 μmol/L (>5.0 mg/dL) from 2 referral hospitals. Interventions – None. Measurements and Main Results – The medical records of 33 foals were reviewed. Twenty‐eight had spurious hypercreatininemia and 5 had acute renal failure. Admission creatinine was not significantly different between the 2 groups (mean [standard deviation]). The creatinine was 1,202 μmol/L (663 μmol/L) (13.6 mg/dL [7.5 mg/dL]) versus 1,185 μmol/L (787 μmol/L) (13.4 mg/dL [8.9 mg/d]) (P=0.96) in each group, respectively, though BUN at the time of hospital admission was significantly higher for acute renal failure foals (P=0.009). In the spurious group, serum creatinine at admission decreased to 504 μmol/L (380 μmol/L) (5.7 mg/dL [4.3 mg/dL]) by 24 hours, and to 159 μmol/L (80 μmol/L) (1.8 mg/dL [0.9 mg/dL]) at 48 hours, and to 115 μmol/L (44 μmol/L) (1.3 mg/dL [0.5 mg/dL]) at 72 hours. Twenty‐three of 28 foals with spurious hypercreatininemia survived to hospital discharge and there was no difference in mean admission creatinine between survivors (1176 μmol/L [628 μmol/L]) (13.3 mg/dL [7.1 mg/dL]) and nonsurvivors (1308 μmol/L [857 μmol/L]) (14.8 mg/dL [9.7 mg/dL]) (P=0.67). Twenty of 28 foals had clinical signs suggestive of neonatal encephalopathy. Conclusion – Creatinine decreased by >50% within the initial 24 hours of standard neonatal therapy and was within the reference interval in all but 1 foal within 72 hours of hospitalization. The diagnosis of neonatal encephalopathy was common in these foals.     

Use of survival analysis as a tool for the genetic improvement of age at first conception in Nellore cattle

Restricted breeding seasons in beef cattle lead to censoring of reproductive data. In this paper, age at first conception (AFC) of Nellore females exposed to the sires for the first time between 11 and 16 months of age, was studied aiming to verify the possibility of genetically advance sexual precocity using a survival model. The final data set contained 6699 records of AFC in days. Records of females that did not calve in the next year following exposure to the sire were considered censored (77.5% of total). The model used was a Weibull mixed survival model including effects of contemporary groups, period (fixed) and animal (random). The effect of the contemporary groups on AFC was important (p < 0.01). Heritabilities were 0.51 and 0.76 in logarithmic and original scales respectively. Results indicate that it is possible to genetically advance sexual precocity, using the outcome of survival analysis of AFC as selection criterion. They also suggest that improvements of the environment could advance sexual precocity too, thus an adequate pregnancy rate for farmers could quickly be achieved.     

Enumeration of Bradyrhizobium japonicum in soil subjected to high temperature: Comparison of plate count, most probable number and fluorescent antibody techniques

The survival of BradyrMzobium japonicum strains in autoclaved and non-autoclaved soil at various temperatures for up to 18 days was determined by plate count, plant infectivity-most probable number (MPN) and modified fluorescent antibody (FA) techniques. The high-temperature tolerant strains studied were BR587, NC1005 and NC1033, and the high-temperature intolerant strains studied were NCI028, 3Ilb24 and 311b123. Each strain was exposed individually in a sandy loam soil at 28, 33 or 37°C under humidity controlled conditions. Those strains reported to be tolerant to elevated temperature in pure culture decreased by <10^1.5 cells g⁻¹ when enumerated by plate count after high-temperature exposure in autoclaved soil. Based on plate counts, the population of two of the three high-temperature intolerant strains added to autoclaved soil decreased by more than 10³ cells g⁻¹ soil after exposure to elevated temperatures. In non-autoclaved soil, the population of all inoculated strains decreased after exposure to elevated temperature when enumeration was by the plant infectivity-MPN technique. In autoclaved soil at 28°C, the correlation between plate count and FA enumerations was significant at the 0.05 probability level for four of the six strains (r² = 0.65). After high-temperature incubation, counts based on the FA technique were not correlated with plate counts of intolerant strains or MPN enumeration of tolerant and intolerant strains (r² = 0.004). Differential survival of B. japonicum strains in autoclaved soil at high temperature as enumerated by plate counts confirms the designation of temperature tolerance made by Munevar and Wollum (1981). However. MPN enumeration of bradyrhizobia in the non-autoclaved system did not follow the original temperature tolerance classifications. Enumeration by FA procedures did not show a decrease in population after exposure to high temperature as observed with the plate and MPN counts. Thus, the FA technique may not adequately indicate population dynamics in short-term ecological studies.     

Induced Ovulation of Southern Flounder Paralichthys lethostigma Using Gonadotropin Releasing Hormone Analogue Implants

Implanted pellets that provide a sustained release of [D-Ala⁶ Des-Gly¹⁰] LHRH-ethylamide (GnRHa) were used to induce maturation and ovulation of Southern flounder Paralichthys lethostigma . Of the 12 females whose ovaries contained follicles with a maximum diameter ≥500 μm, 11 ovulated for the first time within 90 h of hormone implantation. Only 1 fish with a maximum follicle diameter less than 500 μm ovulated within 2 wk after implantation. Ovulated eggs were manually stripped from the females and mixed with sperm from several males. Most females were spawned 1 to 3 times on consecutive days with variable fertility. One female was spawned 11 times producing 668,000 eggs. Fertility was evaluated by examining the incubated eggs for early stages of embryonic cleavage. The percentage of fertile eggs in subsamples of incubated eggs ranged from 7–95%. The results indicate that GnRHa implants can be used to induce repeated ovulation in this species. The variability in fertility is discussed in relation to egg quality.     

Effects of wind-driven rainfall on stemflow generation between codominant tree species with differing crown characteristics

Meteorological influences on the variability of stemflow generation can affect the hydrology, ecology and soil chemistry of wooded ecosystems, yet the effects of directional wind-driven rainfall on differential stemflow production remain relatively un-researched. This study examines the correspondence of directional wind-driven inclined rainfall with stemflow generation in individual tree crowns utilizing multiple correspondence analysis (MCA) and intrastorm observations at 5 min monitoring intervals. In general, preferential stemflow generation at Fair Hill was observed during episodes of inclined rainfall driven by wind from the east to north-northeast (33.76-101.25°). This was supported by MCAs which produced significant correspondences between stemflow production and periods of inclined wind-driven rainfall for nearly all monitored storm events. Intrastorm plots of stemflow production from dominant and subcanopy trees of each codominant species (Fagus grandifolia Ehrh. (American beech) and Liriodendron tulipifera L. (yellow poplar)) also verified this correspondence. Interspecific canopy characteristics of L. tulipifera and F. grandifolia affected crown position, canopy structural characteristics, and, thus, the canopy's response to inclined precipitation. The greater vertical canopy depth observed for F. grandifolia trees enabled them to more efficiently capture inclined rainfall for enhanced stemflow production; whereas, the greater horizontal surface area of L. tulipifera canopies enhanced their droplet capture efficiency and subsequent stemflow generation for periods of un-inclined rainfall. As inclined wind-driven rainfall occurred within a majority of rain events at this site, preferential stemflow production may be a significant process to consider when examining the spatial distribution of canopy-derived water fluxes to the forest floor of wooded catchments under similar meteorological conditions.