The effects of cover cropping on yield and weed control of potato in a transitional system

Cover cropping can have various beneficial effects to the cropping system such us the increase of soil nutrient content and weed suppression. In this respect, the species used for covering is of great importance. This paper reports results on the yield and weed control effects in potato crops preceded by different cover crops over a 2-year period (2003 and 2004) in Central Italy (Viterbo). Results were obtained in the frame of a more complex study set up in 2002 where in a 3-year chick-pea/potato/tomato rotation, each crop was preceded by 7 different soil managements: 5 cover crops (rapeseed, Italian ryegrass, hairy vetch, snail medick and subclover)+1 unfertilised weedy fallow (cover crop absent)+1 control (weedy fallow fertilised with mineral N at a rate of 170kgha⁻¹ for potato). Two different weed control regimes in potato were also applied [weed-free crop (1 inter-row hoeing+1 hilling up+manual weeding on the row); mechanical control (1 inter-row hoeing+1 hilling up)]. Cover crops were sown in September and cut and ploughed just before potato planting in March. The potato crops following the cover crops were only fertilised with green manure. Averaged over years, all the cover crops produced more above-ground dry biomass than the weedy fallow (4.79tha⁻¹ on average vs 2.36tha⁻¹). Hairy vetch and subclover accumulated the highest N in the incorporated biomass (169 and 147kgha⁻¹), followed by snail medick (108), rapeseed (99), ryegrass (88) and weedy fallow (47). Rapeseed and ryegrass were the most efficient weed suppressors and had the least proportion of weed biomass (<1%) of the total produced by the cover, while they also reduced weed emergence in the following potato crops (8.8plantsm⁻² vs 25.5plantsm⁻² with all other cover crops). Following subclover and hairy vetch the potato crop yield was similar to that obtained by mineral N-P-K fertilisation (48.5tha⁻¹ of fresh marketable tubers). Mechanical weed control compared to weed free crop always reduced potato yield and the reduction, averaged over years, was greater in N-P-K mineral fertilised control (-23.6%) and smaller in ryegrass (-7.9%).