A comparison of the genital features of Arion urbiae and A. anguloi suggests that the species are extremely similar, if not identical. This hypothesis is supported by an electrophoretic analysis of 13 putative enzynme loci, which shows that the two species are also genetically yery similar (I = 0.947), while the related A. subfuscus consists of two distinct genetic types (I = 0.421). These results are further confirmed by a study of esterase profiles obtained with isoelectric focusing. It is therefore concluded that A. urbiae and A. anguloi are most probably conspecifie, whereas the genetic types of A. subfuscus may represent two different species.
The objective of the current study was to quantify the response of pasture to phosphorus (P) fertilizer application and legume introduction, by measuring herbage yield, nitrogen (N) and P content, and weight gain of calves in native pastures of Uruguay. Quantitative relationships between pasture characteristics and post-weaning daily live weight gain (DLWG) were also examined. The treatments studied were native grassland (NG) and improved pasture, oversown with Lotus corniculatus L. and Trifolium repens L. with annual applications of either 13 and 26 kg P/ha. From 1996 to 2001 the treatments were evaluated each year with a new group of calves. Total herbage yields of the oversown pastures were not always higher than NG in the initial years, but legume production increased, although without significant differences between P rates on legume or total yield. This was also reflected in the N and P status of the swards. In the last 2 years legume proportion had declined to <0·1, but total herbage yield was significantly higher in the improved pastures. The average DLWG over the 6 years of measurements were 0·319, 0·478 and 0·586 kg/day for NG, P1 and P2, respectively, with average total live weight gain increased 1·8-and 2·5-fold by the legume introduction and annual addition of 13 and 26 kg P/ha, respectively. The study demonstrated that the evaluation of pasture response to P application should not be limited to assessing forage yield increase. Phosphorus availability in the herbage was a better predictor of animal performance than pasture yield. The study highlights that the benefits of oversowing and fertilizer inputs are short-lived, as withholding of fertilizer in the last 2 years resulted in a loss of sown legumes and decline in animal production.
Organic wastes have been reported to reduce saturation of the exchange complex by Al in Al-rich acid soils. For 3 years, the main soil fertility properties were studied in plots sown with mixed pasture species. These plots were fertilized with cattle slurry, dairy sludge (DS), or granulated broiler litter (BL) in comparison with mineral fertilizer. Al saturation levels were low after the initial inorganic liming treatment (19.00-33.71%) but tended to rise under all treatments (21.09-61.37%) except BL (8.45-30.98%), which was also associated with the highest average soil pH and the highest average levels of exchangeable Ca2+, Mg2+, and K+. Treatment DS performed similarly to mineral fertilizer in most respects, but it led to greater available P levels. Under the dry conditions of the second and third years of the study, BL and DS treatments were associated with significantly greater forage yields than the other treatments. Under DS treatment, available P levels were too low to allow the maintenance of mixed pasture, clover being eliminated by the less P-dependent species.
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