Measurement of mulberry shrubs grazed by cattle

C. F. Cereti, F. Rossini & U. Francia
Dipartimento di Produzione Vegetale
Università degli Studi della Tuscia, Viterbo, Italy

INTRODUCTION

The necessity to provide alternative sources of forage in certain periods of the year has encouraged research on new crops. Some deciduous shrubs, including mulberry, can contribute to balancing forage supply during the summer months. Mulberry foliage can be considered a good protein supplement during the summer period, improving the intake of free-range cattle in marginal areas.

The measurement, evaluation and agronomic management of shrubs introduced in the Mediterranean forage system has been problematic. Among the various methods proposed for indirect evaluation of forage shrub production, photography appears to be most valid, both in measurement speed and reliability (Cereti and Rossini, 1992; 1993).

A trial was carried out to evaluate the practicality of the photographic method and to learn about mulberry productivity and relative grazing merit.

METHODS

A two-year trial was carried out in 1992-93 at Tormancina, centra1 Italy (42° latitude north). In the first ten days of August a herd of Maremmana cows grazed on 50 mulberry plants (M. alba). The shrubs had been planted in 1988 at a density of 5 000 plants/ha (2 x 1 m) on the volcanic soil commonly found in Roman hillsides. In 1990 the shrubs were subjected to mechanical pruning at two different heights (10 and 80 cm). The photography and scanner technique for mass evaluation was used (Cereti and Rossini, 1992) with a green filter and a black opaque background to reduce disturbances caused by natura1 illumination (areas of shrubs in shadow, shadow on the screen). Shrub volume difference (?V), before (Vl) and after grazing, was used to determine DM (DM) availability and intake. The relationship between the dimensiona1 parameters and the DM was obtained by manually stripping the leaves each year using 15 sample shrubs. Having observed that cattle feed from shrubs up to 180 cm, DM was only considered available up to this height.

RESULTS AND DISCUSSION

There was more rainfall in 1992 than in 1993. Good soil humidity was maintained up to the second half of July 1993. The relation between standing dry phytomass (g) and mean shrub volume before defoliation or Vl (dm3) was:

Standing dry phytomass = 0.71 Vl + 3.08

r2 = 0.95**

The relation was not influenced by pruning height of shrubs and, thus was used for the calculation of shrub DM availability (Table 1).

TABLE 1

DM availability (g/plant) during the two-year trial

Year	Pruning height
	10 cm	80 cm	Mean
1992	50.2	101.2	74.6
1993	60.0	120.6	92.0
Mean	55.1a	105.8b

Means were significantly different at the 1 percent level.

The relationship between the DM removed by the animals (g) and the average volume difference (dm3) of the shrubs taken before and after grazing (V) was the following:

Dry phytomass removed = 1.13V + 9.15

r2 = 0.93**

For this relationship, the dimensional parameters and the DM of the sample shrubs were measured not only before and after total leaf stripping by browsing, but also at intermediate stages in order to include various degrees of use. The DM estimate using this relationship did not differ from that obtained using the previous relation. The shrubs pruned at 80 cm produced, on average, more than double that of those pruned at 10 cm (114.6 g/plant compared with 50.4 g/plant).

In this case the quantity of DM resulted comparable to that actually used by the animals. The explanation could be that during the two years in which the trial was carried out the shrubs were completely stripped by the animals.

CONCLUSION

The indirect evaluation of shrub forage production determined by a photographic survey could be applied in normal operative conditions while maintaining a high degree of certainty. Moreover, research results show that the higher cutting height enables greater productivity of mulberry, even after three years of pruning. The shrubs pruned at 80 cm need frequent attention (every two or three years) as they tend to increase the average production leve1 rapidly above requirement (Correal, Otal and Sottomayor, 1990). The 10 cm pruning can be practised only during the first or second year after planting to make the shrubs suitable for browsing.

BIBLIOGRAPHY

Cereti, C. F. & Rossini, F., 1993. An attempt to measure indirectly shrub’s biomass. In Fodder trees and shrubs in the Mediterranean production systems: objectives and expected results of the EC research contract. p.187-191. CEC.

Cereti, C.F. & Rossini, F. 1992. Stima, mediante l’analisi d’immagine, della fitomassa asportabile e asportata da arbusti di Medicago arborea L. Riv. di Agron., 4: 536-541.

Correa1, E.; Otal, J. and Sottomayor, J.A., 1990. Effect of grazing frequency and cutting height on the production of browsing biomass of Oldman saltbrush (Atriplex nummularia L.) in S.E. Spain. Sixth Meeting of the FAO European Subnetwork on Mediterranean Pastures and Fodder Crops, Bari (Italy), 17-19 October.