In drought-prone environments, sweet sorghum and sorghum-sudangrass hybrids are considered worthy alternatives to maize for biogas production. The biomass productivity of the three crops was compared by growing them side-byside in a rain-out shelter under different levels of plant available soil water (PASW) during the growing periods of 2008 to 2010 at Braunschweig, Germany. All crops were established under high levels of soil water. Thereafter, the crops either remained at the wet level (60-80 % PASW) or were subjected to moderate (40-50 % PASW) and severe drought stress (15-25 % PASW). While the aboveground dry weight (ADW) of sweet sorghum and maize was insignificantly different under well-watered conditions, sweet sorghum under severe drought stress produced 27 % more ADW than maize. The ADW of sorghum-sudangrass hybrids significantly lagged behind sweet sorghum at all levels of water supply. The three crops differed markedly in their susceptibility to water shortage. Severe drought stress reduced the ADW of maize by 51 %, but only by 37 % for sweet sorghum and 35 % for sorghum-sudangrass hybrids. The post-harvest root dry weight (RDW) in the 0-100 cm soil layer for maize, sweet sorghum and sorghum-sudangrass hybrids averaged 4.4, 6.1 and 2.9 t ha À1 under wet and 1.9, 5.7 and 2.4 t ha À1 under severe drought stress. Under these most dry conditions, the sorghum crops had relatively higher RDW and root length density (RLD) in the deeper soil layers than maize. The subsoil RDW proportion (20-100 vs. 0-20 cm) for maize, sweet sorghum and sorghum-sudangrass hybrids amounted to 6 %, 10 % and 20 %. The higher ADM of sweet sorghum compared with maize under dry conditions is most likely attributable to the deep root penetration and high proportion of roots in the subsoil, which confers the sorghum crop a high water uptake capacity.

No abstract

No abstract

the traditional classification, according to the primary storage carbohydrate, into sucrose-, fructan-, and starch-Introduction of the fructan crops root chicory (Cichorium intybus crops, is becoming increasingly inappropriate. A recent L.; RC) and Jerusalem artichoke (Helianthus tuberosus L.; JA) into example is the creation of a fructan beet through inagricultural production systems is desirable to diversify crop rotation. Field experiments were conducted to compare the agronomic perfor-serting into sugarbeet a single gene from Jerusalem artimance of RC and JA with sugar beet (Beta vulgaris L.; SB). One choke that encodes an enzyme which converts sucrose set of cultivars during 1995, 1996, and 1997 and an additional set in 1997 to fructan (Sé venier et al., 1998). From an agroecological were grown on a sandy loam soil (Haplic Luvisol) at Braunschweig, point of view, it is desirable to have for each kind of Germany. Crops were cultivated with and without supplemental irrigaagricultural raw products one or few alternative crops, tion, complete and no weed control (1995 and 1996), and N fertilization instead of a single multiple-use major crop. However, rates of 0, 60, and 120 kg ha Ϫ1 . Severe water stress caused significant under present conditions in agriculture, root chicory and but similar storage organ yield losses in all crops, whereas mild water Jerusalem artichoke will only become true alternative stress mainly affected JA yields. Averaged across years and N levels, sugar crops if the raw materials are produced at prices storage organ yield losses through weed competition under irrigation competitive to those of established high yielding crops. amounted to 70, 47, and 8% in SB, RC, and JA, respectively. Averaged across years, in the absence of water and weed stress, SB, RC, and

The cup plant (Silphium perfoliatum L.) is discussed as an alternative energy crop for biogas production in Germany due to its ecological benefits over continuously grown maize. Moreover, a certain drought tolerance is assumed because of its intensive root growth and the dew water collection by the leaf cups, formed by fused leaf pairs. Therefore, the aim of this study was to estimate evapotranspiration (ET), water-use efficiency (WUE) and the relevance of the leaf cups for the cup plant's water balance in a 2-year field experiment. Parallel investigations were conducted for the two reference crops maize (high WUE) and lucerne-grass (deep and intensive rooting) under rainfed and irrigated conditions. Root system performance was assessed by measuring water depletion at various soil depths. Transpiration-use efficiency (TUE) was estimated using a model approach. Averaged over the 2 years, drought-related above-ground dry matter reduction was higher for the cup plant (33 %) than for the maize (18 %) and lucerne-grass (14 %). The WUE of the cup plant (33 kg ha À1 mm À1 ) was significantly lower than for maize (50 kg ha À1 mm À1 ). The cup plant had a lower water uptake capacity than lucerne-grass. Cup plant dry matter yields as high as those of maize will only be attainable at sites that are well supplied with water, be it through a large soil water reserve, groundwater connection, high rainfall or supplemental irrigation.