3. Alternatives to the traditional land-use system in alentejo, portugal, with special reference to soil tillage (alternative zum traditionellen landnutzungssystem im alentejo, portugal, unter besonderer ber_cksichtigung der bodenbearbeitung.)
Göttinger Beitrege zur Land- und Forstwirtschaft in den Tropen und Subtropen, 31, 1988, 188 pp.
The present paper deals with the problems of the land-use system currently applied in Alentejo which have arisen since agriculture has been mechanized. A review of the history of development of land use in southern Portugal gives the background for understanding the severe problems that faces agriculture in this region.
In field trials on two sites with different levels of soil productivity, a comparative study of the traditional tillage and cropping system, with two alternatives each, was made. The choice of alternatives aimed at reducing the costs for cereal production and exploring the possibilities for improving fodder production in cereal crop rotations. For this purpose, conservation tillage methods, on the one hand, and clover and forage crops, on the other, were compared with the traditional tillage and cropping system. Supplementary investigations of soil-related parameters, herbicide use and cultivation methods for sunflower provided additional information about the possibilities and limitations of the reduced tillage methods.
On average over the three experimental years, the different tillage treatments (ploughing, scarifying and direct drilling) had little effect on cereal yields and forage and pasture dry matter production. However, marked differences in cereal yields between tillage treatments could be detected for single years, weed infestation being the main factor in producing these differences. In contrast to the sandy soil, the triple-disc direct drilling system revealed some problems in assuring a satisfactory cereal plant stand on the heavy clay soil. Yet it was on the light-textured soil where the reduction of tillage intensity tended to produce slightly lower yields.
The triple-disc system proved not to be an appropriate direct-drilling unit for the seeding of sunflower on heavy clay soils. An adequate plant density could only be achieved with seedbed preparation. However, in a trial in which seeding was done by hand without preceding tillage operations, it was found that the direct drilling method itself can be successful in producing sunflower on clay soils.
Early sowing of sunflower is possible and may result in a considerable yield increase. Early sowing in winter, however, is possible only on non-tilled soil. Variation in plant density proved to have little effect on sunflower yield. No differences in the yield of sunflower were observed between fertilized and non-fertilized plots.
Certain crop rotation effects could already be observed after three years of experimentation by considering the effects of the preceding crops on the following ones. To some extent, these effects varied between tillage treatments. On the more productive clay soil, it was mainly the forage crop that showed positive effects, due to the suppression of weeds, whereas on the sandy soil it was the following wheat crop, mainly after ploughing. The regrowth of the green fallow was dependent not only on the soil tillage treatment but also on the herbicide level used on the preceding cereal crop. After one or two years of cereal production, ploughing resulted in a pronounced delay of pasture regrowth and in a reduced total dry matter production. The plant group most affected by ploughing were the legumes.
The higher the herbicide level, the lower the total dry matter production measured. The reverse was true for legume yield. A considerable decrease in surface runoff and an even greater increase in eroded soil was observed in small erosion trials when tillage intensity was reduced.
The investigation of physical, chemical and microbiological parameters of the soil as affected by the tillage method revealed, in some cases, large differences between tillage treatments.
Reduction in soil tillage led to a marked decrease in the nitrate content of sandy soil. The reverse was observed with respect to the soil respiration rate in the top surface layer. Oxygen concentration in the atmosphere of the topsoil under water-logging conditions was found to be less under direct drilling. However, no correlation could be found between oxygen concentration and plant growth.
Small or no differences between tillage treatments were detected in the root development of wheat, bulk density, soil temperature and soil water content at the end of the vegetation period of wheat.
The results are discussed with regard to the comparison of the traditional tillage and cropping system with the chosen alternatives and in the context of results obtained in tillage studies reported by other authors. The study concludes with a comparison of the economics of the different tillage methods, indicating an increase of soil productivity if reduced cultivation or direct drilling are properly performed.
Finally, prospects for changes needed in plant production in the Alentejo are given, and further research subjects, such as weed control and the suitability of other soil types for reduced cultivation, are proposed.
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Traditional land-use systems
Latin America, Brazil, tropical lowlands, Amazonia, indigenous farming systems, study, land tenure, deforestation, potential plants, agroforestry, non-farm activities, rural industry, employment, DESFIL
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