Crop Rotation and Soil Pathogens — Trends in Germany

The need to cut costs has led to a simplification of crop rotation in several fields of plant cultivation. The results of Thormann, who has grown wheat continuously on parts of his farmland for 10 years, are discussed. Also, the preliminary results of our own experiments with increasing proportions of wheat and barley suggest that more wheat and barley may be cultivated in crop rotation than is allowed according to the conventional limits determined by the increase of foot rot diseases and cereal root eelworm. Even in successive crops of maize the problem of soil-borne pathogens can be tackled: the spread of blister smut is stopped by the control of the frit fly and by selection of tolerant varieties; root and stem rots of maize are overcome by the selection of appropriate varieties, too. On the contrary, the potato root eelworm is a serious pest in all sites of intensive potato production. Only an integrated control including the use of resistant varieties and the application of nematicides gives success. Much research work has to be done mainly to get more information on the biotical defence mechanisms of the soil.     

Aerial Application of Chemicals at Low and Ultra-low Volume Against Main Pests of Citrus and Olive Trees in Tunisia and Libya

Encouraging results were obtained in low and ultra-low volume aerial applications against Ceratitis capitata Wied. in Tunisia (Malathion LV 96%) and against this pest and against Dacus oleae Gmel. in Libya (with Malathion LV, phosphamidon 50 and 100% a.i. and dicrotophos 100%). The mixture rates of insecticide and bait were also considered.     

Forestry in the North Cheviot Hills

The history of the woodlands on the igneous rocks of the NorthCheviot Hills is briefly reviewed, and site factors are described.The chief silvicultural problem is selection of species, particularlyon steep exposed hills, and details of performance of variousspecies in this area and on similar Scottish sites are given.The relationship of forestry to existing grazing agricultureis discussed, and there is a good case for further extensiveafforestation on economic grounds. This need not conflict withthe use of the area as a National Park. Forestry has an importantsociological role, in halting rural depopulation.     

THE USE OF GRAZING-ANIMAL OBSERVATIONS IN THE EARLY STAGES OF PASTURE EVALUATION IN THE TROPICS

The use of grazing-time records for the estimation of grass species consumption was investigated in the context of two small-plot grazing trials. It was found that sampling errors were significantly lower than those involved in the cutting techniques used and that a high level of repeatability of results could be obtained.
The overall correlations between fresh-weight yield estimates from sample cuts and grazing records for individual plots were found to be 0·57*** and 0·72*** in the two trials. The bias that was introduced into some of the estimates of species yield appeared to be corrected through the use of palatability data.
It is concluded that the use of grazing-time records for yield estimation amongst species of broadly similar growth habit may have a definite potential in tropical Africa, but that the method requires further testing before being widely adopted.     

How long do honey-bees carry germinable pollen on them?

Bees are used to pollinate plants in isolation cages. Usually the bees have previously flown about freely in the open air and may have gathered pollen from the same plant species.Now the question arises whether the bees can contaminate with this pollen plants with which they are enclosed in an isolation cage. In this connection a number of experiments were undertaken to find out how long bees are loaded with germinable pollen. It appeared that the risk of contamination was practically eliminated by keeping the bees in a house or empty isolation cage for 12 hours.     

A Critical Look at Home Timber from the 'Trade's' Point of View

In planning forest management we have the considerable advantagesin Great Britain of an almost clean sheet, fast growth, amplespecies, resourceful engineers, and inexhaustable markets. Wemust organize so that it pays to grow trees. The kind of timberwanted is discussed; how it should be presented for sale; annualquantities needed by an efficient sawmill; and the level ofprices to be paid.     

Sectional notes

American Journal of Potato Research -