Performance of overwinter cover crops in coastal Lebanon

Abstract EN

The effect of the cover crops, narbon vetch (Vicia narbonensis), oat (Avena sativa), forage radish (Raphanus sativus), on weed suppression and soil nitrogen was studied in field conditions overwinter.

The impact of their residues on the productivity of a subsequent corn crop was followed in the summer of the same year.

Between mid-November and March oat produced, on a dry weight basis, 915 g m-2 against 402 g m-2 for narbon vetch and 292 g m-2 for radish.

Consequently, weeds were suppressed best in the presence of oat.

Narbon vetch was less effective than radish in controlling weeds, as it was slower to get established.

In terms of mineral nitrogen, soils occupied by radish (13.1 mg kg'1 soil) presented smaller concentrations of ammonium-N than those by vetch (18.7 mg kg'1 soil) and the control (19.7 mg kg'1 soil).

Following the overwinter cover crops, plots were split into one half where roots only were incorporated, and another half receiving whole plants.

Residues of whole plants promoted higher production of corn in the booting and flowering stages, as compared to roots only.

At the 50% dough stage, the highest dry matter yield was 7.6 Mg ha'1 after narbon vetch.

Corn yield was the smallest after oat, due to N immobilization.

This was demonstrated, using the litter bag technique, when oat residues (15.6 g N kg-1) lost 31% of their N against 66% for radish residues (21.1 g N kg-1).

For an effective control of weeds and nutrient recycling a cover crop, such as oat, is most efficient.

In this case, the succeeding summer crop needs to receive some extra nitrogen.