Effects of surfactant use and peat amendment on leaching of fungicides and nitrate from golf greens

Soil water repellency in golf putting greens may induce preferential “finger flow”, leading to enhanced leaching of surface applied agrochemicals such as fungicides and nitrate. We examined the effects of root zone composition and the use of the non-ionic surfactant Revolution on soil water repellency, soil water content distributions, infiltration rates, turf quality, and fungicide and nitrate leaching from April 2007 to April 2008. The study was made on 4-year-old experimental green seeded with creeping bentgrass (Agrostis stolonifera L.) ‘Penn A-4’ at Landvik in southeast Norway. Eight lysimeters with two different root zone materials: (i) straight sand (1% gravel, 96% sand, 3% silt and clay, and 4 g kg⁻¹ organic matter) (SS) and (ii) straight sand mixed with Sphagnum peat to an organic matter content of 25 g kg⁻¹ (SP) were used in this study. Surfactant treatment reduced the spatial variability of water contents, increased infiltration rates and reduced water drop penetration times (WDPTs) by on average 99% in and just below the thatch layer. These effects were most evident for SS lysimeters. Surfactant treatment resulted on average in an 80% reduction of total fungicide leaching, presumably due to reduced preferential finger flow facilitated by decreased soil water repellency. Peat amendment reduced fungicide leaching by 90%, probably due to increased sorption of the fungicides to organic matter. Nitrate leaching was also smaller from surfactant-treated straight-sand root zones, but this effect was not significant. The use of trade names in this paper does not imply endorsement of a product.     

Virulence of entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) against Tipula paludosa (Diptera: Tipulidae), a turfgrass pest on golf courses

The European crane fly (ECF), Tipula paludosa Meigen feeds on leaves, crowns, and roots of cool-season turfgrasses causing damage to residential lawns and golf courses. A laboratory study was conducted to determine the susceptibility of ECF larvae to four commercial entomopathogenic nematode (EPN) species (Heterorhabditis marelatus, H. megidis, Steinernema carpocapsae and S. feltiae). The virulence of four S. feltiae isolates recovered from golf courses in Quebec and Ontario were also compared to a commercial strain. LC₅₀ values of EPN against late instar ECF larvae were 152, 562, 763, and 3584 for S. feltiae, H. megidis, H. marelatus and S. carpocapsae, respectively. When non-feeding (without grass seedling), ECF larvae mortalities decreased for all nematode species and concentrations tested. At 25°C, LC₅₀ values for the two most virulent indigenous S. feltiae were 129 and 187 nematodes/larva, not different from the commercial strain. At 5°C, the commercial S. feltiae was more effective than both BIC14A and RE6A isolates against ECF larvae. However, at 15°C, BIC14A was the most virulent at the low concentration of 200 IJs/larva.     

The sensitivity of shoot growth of corn to the least limiting water range of soils

The least limiting water range (LLWR), the range in soil water content within which limitations to plant growth associated with water potential, aeration and mechanical resistance to root penetration are minimal, has been proposed as an index of the structural quality of soils for crop growth. An hypothesis that is implicit in the proposed use of LLWR as an index of soil structural quality is that crop growth is negatively related to the proportion of the total number of measurements in which the water content falls outside the LLWR (p_out) and therefore given a certain climate positively related to the magnitude of the LLWR. The objective of this investigation was to test the hypothesis that plant response, specifically shoot growth rate of corn (Zea mays L.), can be functionally related to p_out and the LLWR of soils. The study was carried out on a farm with a side-by-side comparison of no-till and conventional-till. Thirty two paired sampling sites were located along the two transects. The LLWR and p_out were calculated for the 0–20 cm depth in each sampling site. Shoot growth rate (SGR) was measured during a 17 and 16 day period in 1992 and 1993, respectively that corresponded to the 10–11 leaf stage. Although the variation in p_out accounted for a larger percentage of the variation in SGR than did LLWR, the correlation between SGR and LLWR was high and justifies further studies to determine if crop yield can be related to LLWR under different soil and climatic conditions.     

The effect of different irrigation treatments on yield and quality of Verna lemon

Verna lemon trees were irrigated by six different treatments: five flood and one drip. Soil and plant water status, yields and fruit quality were measured. The drip-irrigated treatment gave higher yield and fruit size. The levels of soluble solids, acidity and sugars in the lemon juice decreased in the treatments that used most water. This is explained by a dilution effect. An erratum to this article is available at .     

The effect of vapor pressure deficit on maize transpiration response to a drying soil

A decline in plant transpiration has been widely observed to occur within a fairly stable range of threshold values of fraction transpirable soil water (FTSW), usually 0.3–0.4. However, the stability of this function has not been compared at various levels of atmospheric vapor pressure deficit (VPD). Soil hydraulic conductivity is likely to be involved in determining the threshold where water supply is limiting. Thus, it was hypothesized that at a high VPD resulting in increased transpiration rates, the FTSW threshold for the decline of transpiration rates as a result of drying soil would be increased. This study was undertaken in controlled environment chambers with two maize (Zea mays L.) hybrids (Pioneer Brand Hybrids `3165' and `3737') so as to subject plants to four VPD levels (1.1, 2.0, 2.9 and 3.6 kPa) during a soil drying experiment. In contrast to the original hypothesis, there was little ( 0.05 FTSW) change in the threshold FTSW in response to increased VPD for either hybrid. In fact, over the narrow 0.31–0.38 FTSW range observed, the two hybrids showed opposite trends in FTSW threshold as VPD increased. These results supported the view that the FTSW threshold for the decline in transpiration with drying soil is stable, showing little sensitivity to changes in VPD.     

The influence of Procambarus clarkii (Cambaridae,Decapoda) on water quality and sediment characteristics in a Spanish floodplain wetland

This study describes the effects of the American red swamp crayfish, Procambarus clarkii Girard, on water quality and sediment characteristics in the Spanish floodplain wetland, Las Tablas de Daimiel National Park. Our short term enclosure study during a summer drawdown revealed that crayfish acted as a nutrient pump that transformed and translocated sediment bound nutrients to the water column. Water quality impoverishment was mainly due to the increase of dissolved inorganic nutrients (soluble reactive phosphorus and ammonia), and a significant increase of total suspended solids occurred likely as a result of crayfish associated bioturbation. At the same time, crayfish reduced the content of organic matter in the sediment and we observed a slight increase of total sediment phosphorus and nitrogen content as a result of crayfish benthic activity. P. clarkii effects, in terms of internal nutrient loading (229.91 mg TP m^–2 d^–1), were shown to be important on a local scale, indicating the significance of internal nutrient supply to water column primary producers particularly under low external supply (summer). Extrapolations to the whole ecosystem, however, revealed a negligible crayfish contribution (0.06%) to total internal nutrient loading (0.035 mg TP m^–2 d^–1). Hence, crayfish spatial heterogeneity patterns are important in global and local matter fluxes and nutrient cycles in wetlands.     

Effects of precipitation on photosynthesis and water potential in Andropogon gerardii and Schizachyrium scoparium in a southern mixed grass prairie

In grassland ecosystems, spatial and temporal variability in precipitation is a key driver of species distributions and population dynamics. We experimentally manipulated precipitation to understand the physiological basis for differences in responses of species to water availability in a southern mixed grass prairie. We focused on the performance of two dominant C₄ grasses, Andropogon gerardii Vitman and Schizachyrium scoparium (Michx.) Nash, in treatments that received ambient rainfall, half of ambient rainfall (“drought” treatment), or approximately double ambient rainfall (“irrigated” treatment). Water potentials of S. scoparium were lower than A. gerardii, suggesting superior ability to adjust to water deficit in S. scoparium. Additionally, drought reduced photosynthesis to a greater extent in A. gerardii compared to S. scoparium. Leaf-level photosynthesis rates were similar in ambient and irrigated treatments, but were significantly lower in the drought treatment. Although stomatal conductance was reduced by drought, this was not limiting for photosynthesis. Leaf δ¹³C values were decreased by drought, caused by an increase in C_i/C_a. Chlorophyll fluorescence measures indicated light-harvesting rates were highest in irrigated treatments, and were lower in ambient and drought treatments. Moreover, drought resulted in a greater proportion of absorbed photon energy being lost via thermal pathways. Reductions in photosynthesis came as a result of non-stomatal limitations in the C₄ cycle. Our results provide mechanistic support for the hypothesis that S. scoparium is more drought tolerant than A. gerardii.