Abstract
Early strategies of crop growth and N acquisition can be critical for determining competitive interactions between weeds and crops. Grain legumes and especially lupins are known to be poor competitors against weeds. Grain legumes are known to have low mineral soil N uptake abilities. However, inter- and intraspecific differences in N uptake ability in relation to below-ground traits have received little attention. Our objectives were (i) to measure differences among lupins for a set of traits associated with early growth and N acquisition; (ii) to examine how this variation compares to differences between lupin and a cereal, triticale, and (iii) to assess if mixing lupin with triticale provides a higher potential than does pure lupin regarding plant biomass and mineral soil N acquisition early in the crop cycle. Lupin (12 genotypes) and triticale plants were grown separately and in mixed species pairs in a replacement design for 1 and 2 months in three rhizotron experiments. Shoot and root biomass, root length, root expansion dynamics, N2 fixation and mineral soil N uptake were measured. Differences among lupin species and genotypes regarding traits related to early growth and to mineral soil N uptake were observed, but all lupins demonstrated slow early growth and low ability to absorb mineral soil N compared to triticale. In lupin-triticale mixture, a contrast in early growth strategies between species induced a higher total soil mineral N uptake compared with pure lupin. Complementarity between lupin and triticale persisted during the second month, when interactions began. This complementarity may allow for reduced competition between species, favouring higher triticale biomass production than in pure triticale, without compromising lupin growth.
Highlights
To reduce dependency on chemical weed control, managing crop competitive ability is a key component of integrated weed management (Jordan 1993)
Most crop competitive ability studies have explored above-ground traits and have identified key traits involved in crop– weed competition such as height, leaf area and branch number (e.g. Christensen 1995; Lemerle et al 1996; Bussan et al 1997; Jacob et al 2016)
The objectives of the present study were (i) to measure the range of variation between lupin genotypes and species for a set of traits with respect to early growth and N acquisition, (ii) to examine how this variation in traits compares to differences between lupin and a cereal, triticale, and (iii) to assess if mixing lupin with triticale provides a higher potential for plant biomass and the acquisition of mineral soil N early in the crop cycle compared with pure lupin
Summary
To reduce dependency on chemical weed control, managing crop competitive ability is a key component of integrated weed management (Jordan 1993). Most crop competitive ability studies have explored above-ground traits and have identified key traits involved in crop– weed competition such as height, leaf area and branch number Christensen 1995; Lemerle et al 1996; Bussan et al 1997; Jacob et al 2016) Such studies have not identified systematically strong correlations between weed suppression and above-ground traits, suggesting that below-ground traits may play a significant role. Crop below-ground competitive ability has been less studied than the above-ground ability despite evidence that competition between plants for water and nutrients is as strong or stronger than competition for light (Martin and Snaydon 1982; Satorre and Snaydon 1992; Casper and Jackson 1997), especially at low nutrient levels (Kiær et al 2013). Few studies have examined above- and below-ground traits during initial growth stages (Thorup-Kristensen 1998)
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