Dollar spot ( Sclerotinia homoeocarpa F.T. Bennett) is a common fungal disease of creeping bentgrass ( Agrostis palustris Hudson). Field experiments were conducted to quantify the effects of leaf surface moisture displacement, N fertilization, and collecting or leaving clippings on severity of dollar spot. Tests were conducted on A. palustris cv. Penncross maintained at 0.6 cm (putting green height) and on turf containing A. palustris cv. Penncross and annual bluegrass ( Poa annua L.) maintained at 1.1 cm (fairway height). Six mowing treatments, four of which displaced morning leaf surface moisture and three of which collected clippings, were imposed on turf fertilized with 0, 36.6, and 73.2 kg N ha −1 in 1992 and 1993. Significant reductions of dollar spot after morning mowing or poling treatments, or both, were recorded on turf at both heights of cut and in both years. Maximum reductions of disease due to mowing treatments across all N levels were 81% on fairway turf in 1992 and 53% on putting green turf in 1992. Collecting or leaving clippings did not consistently affect the severity of dollar spot. The effects of N fertilization were significant at various levels in both tests and in both years. Maximum disease reductions comparing 0 and 73.2 kg N ha −1 were 57% on putting green turf in 1992 and 44% on fairway turf in 1993. There were no consistent interactions in the severity of dollar spot among mowing treatments and N levels.
Pearl millet [ Pennisetum americanum (L.) Leeke] is an annual warm season (C4) grass that has a high yield potential during summers when cool season species are heat‐stressed and unproductive. In two field trials, 650 kg round bales were made from long (>100 cm) or short (chopped) (≈15 cm) forage and at bale chamber pressures of 421 or 842 × 10 3 Pa. After 24 h of wilting, forage moisture concentrations at Trial 1 and Trial 2 were 771 and 583 g kg −1 , respectively. The higher baling pressure increased both mass and density of bales ( P < 0.05). Length of cut had no effect on bale weight or density. Core temperatures were lower in higher density bales when the concentration of forage moisture was lower. Water‐soluble carbohydrate concentrations were lower in silages made from the shorter forages ( P = 0.013). Nutritive value of silage decreased during 8 mo of storage regardless of treatment. Baling chamber pressure and forage chopping treatments did not affect neutral detergent fiber (NDF) or in vitro dry matter digestibility (IVDMD) of post‐storage silage. Acidity of silage ranged from pH 4.13 to 5.31. Lactic acid concentrations were lowest in silage in Trial 1 made from the wetter forage (771 g kg −1 ) when chopped to 100 cm. Listeria was present in bales made from the wetter forage. Clostridium botulinum was detected in silage made from chopped forage when baled at low chamber pressure.
Calculating forage availability is challenging for managers of grazing systems due to the spatial heterogeneity of swards. Remote sensing applications may help to overcome this problem through estimates of biomass made with reflectance data. The objectives of this study were to (i) estimate herbage mass using an active, on-the-go, ground-based, narrow band sensor to calculate the normalized difference vegetation index (NDVI), (ii) determine if NDVI may be used to assess spatial variability of herbage mass of grasslands, and (iii) determine if NDVI may be used to evaluate management of grazing systems. The NDVI was measured using an active ground-based sensor, the GreenSeeker (Ntech Industries, Ukiah, CA). In tall fescue [Schedonorus arundinaceus (Schreb.) Dumort], NDVI was correlated with biomass determined by destructive harvesting (r2 = 0.68) and also with a calibrated rising plate meter (RPM) (r2 = 0.54). Semivariograms revealed that NDVI sampling intervals of 0.76 m adequately described the spatial variability structure of grazed swards. The frequency distributions of sward biomass derived from NDVI may reflect the foraging strategies of cattle. Negative skewness and high kurtosis are consistent with selective grazing, while positive skewness and low kurtosis are consistent with less diet selectivity. Frequency distributions also improved definition of available forage within each field. We concluded that spatial properties of grassland biomass may be derived from high resolution NDVI and RPM data and could be used to evaluate conditions of grassland landscapes and to aid decision-making of managed grazing systems.
Water potentials of flag leaves and ears on the same tiller of Kopara wheat were measured soon after ear emergence by a pressure-bomb technique. Water potentials of ears were nearly 0.5 bar higher than those of flag leaves. At soil water levels (0—15 cm) of 20%, water potentials of —8 to —9 bars were recorded at 0900 hr on a day of high solar radiation with relatively little advective heat transfer. In non-irrigated wheat, soil water levels were well below the permanent wilting point, and the water potentials of the ears were lower than— 20 bars. Nitrogen fertiliser had no direct effect on ear water potential, but in non-irrigated wheat it depleted soil water, probably by increasing leaf area index and transpiration. As a result soil water levels in non-fertilised, non-irrigated plots were well above the wilting point, and the water potentials of the ear of wheat growing in them were similar to those which were irrigated.
Abstract Red clover (Trifolium pratense L. cv. ’Grasslands Turoa‘) established with wheat (Triticum aestivum L. cv. Aotea) in Canterbury was under considerable water stress during reproductive stages of deveiopment of the cereal, even when the soil water potential in the top 15 ern was approximately —1 bar. It is postulated that the unfavourable light and moisture environment of the red clover under wheat severely restricted root development to a few centimetres of the soil surface, where much less water was available than at greater depths.
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