Competitive interactions between chick-pea genotypes and weeds

Growing chick‐pea in sustainable systems requires the use and development of more competitive genotypes which can complement the effects of reduced input weed control. A 2‐year study assessed the competitive ability of 13 genotypes grown in either the presence or absence of weeds, in a split‐plot design including the weeds in pure stands. Crop and weed density, phenology, relative biomass of crop (RB_c) and weeds (RB_w), crop yield characters, crop biometric traits in the absence of weeds, relative biomass total of mixtures (RBT) and crop competitive ability (C_b = ln RB_c/RB_w) were recorded. Lines C136, C120, C101 and C106, and cultivars Pascià, Visir and Sultano gave the best seed yield in the absence of weeds (1.8–2.0 t ha^?1 DM). Weeds reduced yield by 75% and 83% in C136 and C133 and by 87–97% in the other genotypes. Weed biomass in mixture (mainly Chenopodium album) averaged 4.42 t ha^?1 DM. Chick‐pea genotypes C136 and C133 were the most competitive, but weeds were more competitive than any of the chick‐peas. C_b was correlated directly to the height of first fertile pod (r² = 0.84) and inversely to the insertion angle of primary branches to the vertical (r² = 0.77). Intergenotypic variation for competitive ability could be exploited in integrated weed control using more competitive genotypes, or used in breeding programmes aimed to develop highly competitive cultivars on the basis of easily screenable characters.     

Focus on ecological weed management: what is hindering adoption?

Despite increased concerns regarding the heavy reliance of many cropping systems on chemical weed control, adoption of ecological weed management practices is only steadily progressing. For this reason, this paper reflects on both the possibilities and limitations of cultural weed control practices. Cultural weed control utilises a number of principles, predominantly: (i) a reduced recruitment of weed seedlings from the soil seedbank, (ii) an alteration of crop–weed competitive relations to the benefit of the crop and (iii) a gradual reduction of the size of the weed seedbank. Compared with chemical control, the general applicability, reliability and efficacy of most measures is only moderate, and consequently, cultural control strategies need to consist of a combination of measures, resulting in increased systems complexity. Combined with the trade‐offs connected to some of the measures, this hampers large‐scale implementation. It is argued that tailoring cultural weed management strategies to the needs and skills of individual farmers would be an important step forward. Research can aid in improving the utilisation of cultural weed control strategies by focussing on a broadening of the range of available measures and by providing clear quantitative insight in efficacy, variability in outcome and trade‐offs of these measures.     

Competition between safflower and weeds as influenced by crop genotype and sowing time

The effects of crop genotype and sowing time on competition between safflower (Carthamus tinctorius L.) and weeds were investigated in a 2-year field study. Each year, safflower was grown as a pure stand and in mixture with a natural weed infestation, mostly represented by Polygonum aviculare L., Fallopia convolvulus (L.) A. Löve and Chenopodium album L., in an additive design including weed stands grown without the crop. Grain yield reduction ranged from about 50% to 80% depending on crop genotype, and was higher under spring sowing (mid-March) than under winter sowing (mid-February). In general, those genotypes incurring the least yield reduction gave the greatest suppression of weed biomass. More competitive genotypes also tended to reduce the proportion of C. album in the weed biomass at harvest, particularly in 1994 (the wetter growing season). The competitive ability of the crop was mainly correlated with its biomass at early growth stages, but was not related to its grain-yielding ability in the absence of weeds. Results showed that more competitive crops may be obtained by sowing the most competitive genotypes early. Selecting for higher competitive ability in safflower does not seem to imply a reduction in grain-yielding ability.