Speaker
Description
1. Introduction
Mechanical weed control is a major element of weed suppression in organic farming systems. In addition to the direct effect on weed growth, mechanical weeding, such as harrowing or hoeing, is known to induce side effects on several soil- and crop-related properties. There is a lack of knowledge regarding the effect of mechanical weeding on soil N dynamics and soil moisture in organic maize cultivation after a legume-rich ley (Gilbert et al. 2009). In the context of efficient use of resources and increasing occurrence of extreme weather events (e.g., drought, heavy rainfall), the impact of mechanical weeding needs to be further examined and reconsidered.
2. Material and methods
A field trial was conducted in two consecutive years (2021, 2022) on a sandy loam in North-West Germany to investigate the impact of mechanical weeding on soil mineral nitrogen (SMN), soil moisture and crop yield in silage maize (Zea mays L). The previous crop in both trial years was grass-clover (Lolium multiflorum LAM., Trifolium pratense L.). Mechanical weed control was performed by harrowing or hoeing three times per growing season and compared to a control treatment without soil disturbance. The two treatments (mechanical weeding (mech): harrowing or hoeing; chemical weeding (chem): herbicide) were arranged in a randomised block design with four replications. For investigating SMN, disturbed soil material was taken from 0-5 and 5-20 cm soil depth directly before harrowing or hoeing and two and four days afterwards, respectively. Additionally, soil samples were taken at greater depths (0-30, 30-60, and 60-90 cm) before sowing and after harvest to calculate net N mineralization according to Kühling et al. (2023). Soil water content was first determined gravimetrically by drying a subsample of each soil sample and then volumetrically using the bulk density determined in field. Maize was harvested manually as whole plants. Weed coverage was determined directly before each mechanical weed control and at harvest using a Goettinger Schaetzrahmen (0.1 m²).
3. Results
In 2021, several events were observed where SMN was up to 47 % lower after mechanical weeding in 0-5 cm soil depth compared to the chemical treatment (32.59 kg ha-1), while in 2022, SMN in 0-5 cm was significantly different between treatments in only one event (12.60/16.05 kg ha-1; mech/chem). Mechanical weeding did not affect SMN in 5-20 cm soil depth but led to higher volumetric water content (VWC) in both soil depths, with differences between years and days of measurement (fig. 1). Both treatments (mechanical and chemical) did not completely suppress weed growth. Weed cover was significantly higher for the mechanical treatment at the third measure (12.67 %) and at harvest (10.07 %) in 2021 than for the chemical treatment (1.42/1.18 %), while no significant effect of the different treatments on weed cover was observed in 2022 (2.88/3.6 %; chem/mech). Net N mineralization and biomass yield were not affected by the different weed control treatments.
4. Discussion
The incorporation of grass-clover residues before sowing enhanced N mineralization, which was indicated by a high net N mineralization and high SMN content in both soil layers and years. Furthermore, compared with those of the chemical control, significantly higher weed coverage was observed for mechanical weeding in 2021 after the third treatment and at harvest. Low temperatures at the time of sowing could have delayed maize development and benefitted weed growth. These results indicate that the difference in SMN content between mechanical and chemical weeding around the third treatment (hoeing) may have occurred due to higher N uptake by weeds in the mechanically weeded plots. In 2022, no difference in weed growth was observed between the treatments, which was also reflected in similar SMN contents. In our study, higher VWC after mechanical weeding was attributed to improved water infiltration. Superficial soil disturbance by mechanical weeding following conventional tillage could have been beneficial due to disrupting the soil crust after rainfall.
5. References
Gilbert PA, Vanasse A, Angers DA (2009) Harrowing for weed control: Impacts on mineral nitrogen dynamics, soil aggregation and wheat production. Soil Tillage Res 103:373–380.
Kühling I, Mikuszies P, Helfrich M, et al (2023) Effects of winter cover crops from different functional groups on soil-plant nitrogen dynamics and silage maize yield. European Journal of Agronomy 148.
| Keywords | harrowing; hoeing; N mineralization; organic farming |
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