This paper describes the extraction of water by field crops of sunflower and sorghum from deep podzolic profiles during a drying cycle encompassing most of the growth period. The work was done to evaluate sunflower as a prospective dryland crop for southern Australia, and data are presented for two contrasting years. Sunflower extracted water more rapidly from all levels of the measured profile (0-2 m). Both species drew similar amounts from the top 1 m, but sunflower took two to three times more than sorghum from 1-2 m, the difference being greater in the year of greater evaporative load. Sunflower exhausted the soil of available water to 150-175 cm, sorghum only to 50 cm, taking progressively less from each successive layer down the profile. Extraction of available water from 0-2 m by sunflower was estimated to be 92%, and by sorghum 64%. In the absence of rainfall during its growth period, dryland sunflower is strongly dependent on the presence of water at depth - for example, at 50% flowering the crop was already drawing two-thirds of its water from below 1 m. This dependence limits the frequency with which the crop may be grown in southern Australia and regions similarly characterised by low effective summer rainfall, high evaporative load, and uncertainty in the time needed for a recharge of the profile sufficient to grow sunflower again. In such environments, sunflower may better be regarded as an opportunity crop than as one featuring regularly in farm rotations.
The use of poplar tree systems (PTS) as evapotranspiration barriers on decommissioned landfills is gaining attention as an option for leachate management. This study involved field-testing the Simultaneous Heat and Water (SHAW) model for its ability to reliably estimate poplar transpiration, volumetric soil water content, and soil temperature at a landfill located in southern Ontario, Canada. The model was then used to estimate deep drainage and to ascertain the influence of a young PTS on the soil water balance of the landfill cover. The SHAW model tended to underestimate poplar transpiration [mean difference (MD) ranged from 0.33 to 3.55 mm on a daily total basis] and overestimate volumetric soil water content by up to 0.10 m3 m(-3). The model estimated soil temperature very well, particularly in the upper 1 m of the landfill cover (MD ranged from -0.1 to 1.6 x degrees C in this layer). The SHAW model simulations showed that deep drainage decreased appreciably with the presence of a young PTS largely through increased interception of rainfall, and that PTS have a good potential to act as effective evapotranspiration barriers in northern temperate climate zones.
Growth and water use were studied in field-grown sunflower and sorghum, mainly in a long drying cycle, though other water treatments were included. When water was plentiful, sorghum was the more productive, but in the drying cycle the order was reversed, largely because sunflower extracted more water. This, together with a smaller leaf area and close control of transpiration rate through stornatal sensitivity to air humidity, ensured a far more favourable leaf water status in sunflower, contributing to its much faster net assimilation rate. In view of the species' different photosynthetic pathways and the large difference in water use efficiency generally associated with these pathways. an unexpected outcome was the smallness of this difference. In the drying cycle, sunflower had the further advantages of a strongly determinate habit and a phenology which was unaffected by drought, even when very severe. Consequently, all plants flowered. In sorghum, drought arrested development, which proved disadvantageous in a continued drought, but turned to dramatic advantage in a late break, when sorghum grain yield increased by 75%, while sunflower responded not at all.
Groundnut rust (Puccinia arachidis Speg.) is widely spread in Zambia and is a new threat to groundnut crops in Africa. Fungicides tested for Cercospora control were also effective when both rust and leafspot occurred and yield increases up to 102% were obtained. The most effective chemicals were chlorothalonil, mancozeb plus benomyl and a mixture of mancozeb, benomyl and fentin.
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