Aurora Sombrero

In barley cropping systems of northern Spain, agronomic practices and weather conditions are key components of weed control efficacy. We compared the short-term effects of conventional tillage with minimum tillage (MT) and zero tillage (ZT), in barley monoculture and barley rotation systems. Weed density and weed species number were measured at tillering and flowering barley stages. We found that tillage system can influence weed density and weed species establishment due to, in part, the available light for weed seeds. The results obtained indicate that the MT system facilitates the prevalence of the grass weed Bromus diandrus Roth (50.37%) and the annual dicots Galium aparine (L.) and Buglossoides arvensis (L.) I.M. Johnst. abundant were high in the MT system too, 43.71% and 43.97% respectively. The germination of these species showed a high dependence on light availability. We saw that barley-monoculture plots had a large infestation of Bromus (71.29%) and barley-rotated plots presented more infestation of Galium and Buglossoides (74.36% and 84.4%, respectively). After herbicide application, weed infestation in conservation systems was reduced in barley-rotated plots compared with barley-monoculture. If conservation systems avoided the presence of dominant weeds, the weight of each weed species was balanced within competitive relationships of the cropping systems. Our results confirmed that MT and ZT systems favour different weed species emergences in barley-rotated plots. The combination of MT and barley-rotated cropping system resulted in greater weed diversity and lower total weed density.

Carbon isotope discrimination (?) has been found to be either positively or negatively related to grain yield of small grain cereals when grown in contrasting environments. In order to clarify a possible association between grain yield of barley ( Hordeum vulgare L.) and ? of mature kernels, five 6-rowed and five 2-rowed barley cultivars were evaluated in 22 rainfed environments of northern Mediterranean Spain. Analyses of variance suggested that the genotypic ? values were more consistent across environments than the genotypic yields. Genotype×environment (G×E) interaction for grain yield was further explored by fitting an AMMI (additive main effects and multiplicative interaction) model. The first 2 multiplicative axes were found significant. The AMMI2 model provided more accurate estimates of genotypic yields within environments than the conventional unadjusted means across replicates. AMMI2 estimates were used for input into cluster analysis, grouping environments that ranked genotypic yields similarly. Three major groups were obtained, with average yields of 2.42 t/ha (cluster I), 3.06 t/ha (cluster II), and 5.16 t/ha (cluster III). The genotypic ranking for ? did not vary substantially across clusters, but it changed for grain yield. The average genotypic yields in the low-yielding cluster I ranked opposite to those in the high-yielding cluster III, suggesting the existence of a crossover point at an intermediate yield level. The association between grain yield and ? for genotypic means within clusters was variable. In cluster I, yield and ? tended to be negatively related, whereas they were positively related in clusters II and III. Genotypes with lower ?, i.e. with higher transpiration efficiency, performed better in low-yielding environments (mostly those grouped in cluster I). On the contrary, a high genotypic ? was of advantage in medium (cluster II) and high-yielding environments (cluster III). This observation supports the assumption that drought tolerance and high yield potential under non-limiting growing conditions may be antagonistic concepts in barley. Genotypic means for kernel number per m 2 and ? were consistently and positively related within clusters, suggesting that a constitutively high ? may have been driven by a large genotypic reproductive sink. The convenience of using ? as a selection criterion in areas exhibiting a considerable G×E interaction for grain yield is discussed.

The superior end‐use qualities and reputation for emergence in poor seed bed conditions has maintained club wheat (Triticum compactum Host) as an important, though small class, of wheat in the Pacific Northwest. Our objectives were to determine yield component development in two agronomic zones representative of the fallow/wheat growing region of the Pacific Northwest and to characterize and compare yield component and spike development in two club and two common wheat (Triticum aestivum L.) genotypes. The experiments were conducted at Moro and Pendleton, OR, in 1988 and 1989, where data were collected on yield components and on spike and kernel characters of identified culms. Yields were significantly higher at Pendleton than Moro. Lower floret fertility at Pendleton resulted in fewer and heavier seeds. Kernel weight was apparently the yield component associated with the yield advantage at Pendleton. Early tiller development at Pendleton also favored the development of spikes with greater capacity for yield component compensation. Differences were identified for yield component development in the cultivars Tres, OR8218, Hill 81, and Stephens; however, total grain yield was not significantly different. Although club spikes were one‐half the length of common spikes, spikelet number was not different between classes. Moreover, the number of fertile spikelets and the percentage of fertile spikelets per spike was significantly greater in club genotypes compared with common genotypes. The club genotypes produced more kernels in 1989 than the common genotypes. Kernel weight was consistently less for club lines. These differences were found in the mainstem and tillers T1 to T4. Kernel weight may play an important role in the early seedling establishment in regions where soil moisture is inadequate at planting.