Abstract
Choosing genotypes with a high capacity for taking up nitrogen (N) from the soil and the ability to efficiently compete with weeds for this nutrient is essential to increasing the sustainability of cropping systems that are less dependent on auxiliary inputs. This research aimed to verify whether differences exist in N uptake and N fertilizer recovery capacity among wheat genotypes and, if so, whether these differences are related to a different competitive ability against weeds of wheat genotypes. To this end, 12 genotypes, varying widely in morphological traits and year of release, were grown in the presence or absence of interspecific competition (using Avena sativa L. as a surrogate weed). Isotopic tracer 15N was used to measure the fertilizer N uptake efficiencies of the wheat genotypes and weed. A field experiment, a split-plot design with four replications, was conducted during two consecutive growing seasons in a typical Mediterranean environment. In the absence of interspecific competition, few differences in either total N uptake (range: 98–112 kg N ha−1) or the 15N fertilizer recovery fraction (range: 30.0–36.7%) were observed among the wheat genotypes. The presence of competition, compared to competitor-free conditions, resulted in reductions in grain yield (49%), total N uptake (29%), and an 15N fertilizer recovery fraction (32%) that were on average markedly higher in modern varieties than in old ones. Both biomass and grain reductions were strongly related to the biomass of the competitor (correlation coefficients > 0.95), which ranged from 135 to 573 g m−2. Variations in both grain and biomass yield due to interspecific competition were significantly correlated with percentage of soil cover and leaf area at tillering, plant height at heading, and total N uptake, thus highlighting that the ability to take up N from the soil played a certain role in determining the different competitive abilities against weed of the genotypes.
Highlights
Breeding activity on durum wheat (Triticum durum Desf.) carried out in Italy over the past 70 years has involved the constant release of cultivars selected to perform well under intensive crop management and characterized by an increased yield potential (De Vita et al, 2010), through the exploitation of Rht genes, which has caused a drastic reduction in plant height and a consequent increase in the harvest index (Giunta et al, 2007)
The present study had as objectives to verify whether differences in N uptake and N fertilizer recovery exist among wheat genotypes that differ in their year of release and, if so, to verify whether these differences are related to a different competitive ability against weeds
On the whole, when wheat was grown in the absence of a competitor, the old genotypes produced a higher grain protein content than the modern varieties
Summary
Breeding activity on durum wheat (Triticum durum Desf.) carried out in Italy over the past 70 years has involved the constant release of cultivars selected to perform well under intensive crop management and characterized by an increased yield potential (De Vita et al, 2010), through the exploitation of Rht genes, which has caused a drastic reduction in plant height and a consequent increase in the harvest index (Giunta et al, 2007) This has resulted in a reduction in the competitive ability of wheat against weeds (Lemerle et al, 1996; Vandeleur and Gill, 2004). It is possible that an important role could be played by the capacity of the crop to compete with weeds for belowground resources, such as water and nutrients, and in particular for nitrogen (N)
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