Abstract

Context: Wheat (Triticum aestivum) has a high capacity to compensate grain yield (GY) at lower seed rates than those commonly assumed, especially in high-yield-potential environments. Objective: Our study aimed at assessing: (i) the response of GY, biomass and harvest index of wheat under two contrasting seed rates; (ii) trade-offs among yield components in response to seed rate; and (iii) the sensitivity of grain and crop N and P content and nutrient use efficiency under conventional and low seed rates in the high-yielding environment of southern Chile. Methods: We evaluated two wheat cultivars - Bacanora (higher grain number and intermediate grain weight) and Kambara (lower grain number and higher grain weight)- at two seed rates, a farmers' seed rate of 350 plants m(-2) (CON) and low seed rate of 44 plants m(-2) with square grid planting arrangement (LSR), under optimum crop management conditions during two growing seasons in southern Chile (Valdivia). We evaluated GY and its components, as well as nitrogen (N) and phosphorus (P) economies. Results: Contrasting results were found between cultivars under LSR. Bacanora fully compensated GY components reaching the same GY under both LSR and CON treatments, while Kambara yielded 12% more under the LSR treatment, compared with that of the CON treatment. The LSR treatment decreased the plant height of both cultivars by 0.14 m (19% and 15% in Bacanora and Kambara, respectively), which improved the harvest index. Under the LSR treatment, Bacanora showed a small decrease in grain number while there was no effect in Kambara. Both cultivars reached higher (P 0.001) average grain weight under the LSR treatment. Furthermore, Bacanora increased grain N concentration and both cultivars improved grain P concentration under the LSR treatment. P uptake and P uptake efficiency were increased (P 0.001 and P 0.01, respectively) under the LSR treatment in both cultivars by 18%. Conclusions: Low seed rate (44 pl m(-2)) with square grid planting distribution results in preserved or increased wheat GY compared with the conventional seed rate (350 pl m(-2)), mainly due to an increase in grain weight in both genotypes. The LSR treatment resulted in decreased plant height, allowing an improved harvest index. Additionally, LSR had also a positive effect on grain P concentration, and a remarkably increased of both P uptake and P uptake efficiency. Implications: Our results offer an opportunity to increase the uptake of nutrients such as P, without any GY penalty and may even increase yields, at least in high yield environments, such as southern Chile.