Sustainable weed management in a lettuce growing conservationist system

Abstract

Soil disturbance, irrigation, and nitrogen fertilization excesses in lettuce crops have reduced the sustainability of the sector and favoured competition against weeds. This study aimed to evaluate the effect of cover crops and nitrogen fertilization management on weed control, weed-species dynamics, and soil seed bank in successive lettuce cultivation under no-tillage. The experiment was carried out in a tropical region during summer and arranged in a (3×4) +1 factorial scheme. Treatments consisted of three soil cover managements (Crotalaria juncea, Urochloa ruziziensis, and fallow) and four nitrogen (N) topdressing rates (0, 60, 120, and 180 kg ha−1) in a lettuce crop under fertigation. A conventional tillage system under more intense soil disturbance was also evaluated at the highest N rate. The results showed that lettuce cultivation on U. ruziziensis stood out regarding weed control. Higher soil disturbance in the conventional tillage increased weed emergence (288.9 and 245.8 plants m−2) compared to the fallow area (13.9 and 38.9 plants m−2), U. ruziziensis (4.2 and 9.7 plants m−2), and C. juncea (56.9 and 20.8 plants m−2) in successive cultivations, respectively. Soil cover management changed the dynamics of weed species emergence, especially in the first cultivation. Nitrogen topdressings did not affect weed dry matter and density at the time of weeding. The average number of non-dormant weed seeds within the 0.0-0.10 m soil seed bank layer reached 7,077 seeds m−2, with no difference among treatments. Therefore, sustainable management of lettuce cultivation using cover crops in rotation, associated with no-tillage, effectively controls weed communities, with emphasis on U. ruziziensis, regardless of the nitrogen fertilization management