Traditional agriculture on sloping fields has always had to combat the loss of soil due to runoff, mainly through very labor-intensive practices such as the construction and maintenance of terraces. On some modern farms, however, strongly oriented toward mechanization (as ours is not):
- inter-row grass cover has to be used to slow runoff;
- organic material has to be added frequently to improve the structure of the soil and penetration of water;
- passage of the tractor between the rows has to be eliminated: only overturning the topsoil to a shallow depth in late fall every 2-3 years; this process also improves the subsequent growth of the grass cover;
- country roads have to be built following the direction of the rows, to interrupt the flow of runoff and direct it to the appropriate pond or drainage system on the farm itself.
The regional authorities have to supply clear, simple recommendations for the organization of the drainage system on the farm, and supply and maintain the drainage system at a higher, multi-farm level.
Political leaders have to recognize and support efforts to prevent runoff at all levels.
At the level of the farm, management of the grass cover is fundamental to prevent and reduce runoff.
In order to rate the effectiveness of different kinds of grass covering, work is ongoing to evaluate four types of management between the rows:
- “Standard” management by the grower;
- continuous overturning of topsoil, simulating inter-row clearing;
- single clearing between the rows once a year in late fall;
- planting of autochthonous grasses to simulate a natural long-lasting grass cover;
- nectariferous grass cover, i.e. blends of grass species capable of attracting insects and thereby increasing biodiversity.
The first results show that continuous overturning of the bare soil generates runoff rich in suspended solids, but the main disadvantage of this option is the formation by the tractor of deep tracks and the difficulty of transiting on them when muddy.
Clearing once in late fall is an interesting option, because it leaves no tractor tracks and improves later regrowth of the grass cover; if done in late fall (November), during the wet season, there is no risk of runoff because the topsoil layer is soft and even the most intense rains can soak into it.
The use of autochthonous species is interesting and is a simple and economic method, available for vineyards. It is important to note that a single planting is seldom sufficient to replace the mixtures of commercial seeds in use for many years, however in case of new vineyards, using autochthonous species can be strongly recommended to increase the diversity of the grass cover.
The nectariferous blend is interesting because it grows very rapidly in mid-autumn and by the end of winter the coverage is 100% so the risk of runoff is very low, as in the case of the single ploughing. It is important to note that this mixture should be used every two inter-rows and a roller-crimper should also be used in a timely manner in late spring to prevent interference with protection of the grapes.
The ability to increase biodiversity, in particular of insects, is proportionate with the extent of use of this mixture, so only its use in most of the vineyard can have significant effects.
In 2020 total precipitation was 1,271 mm in 85 days of rain, very close to the average for the last 27 years (1,308 mm (340 standard deviation) in 95 days of rain) (ARPAV, email@example.com).
In the Soave district, where the slopes are very steep (>20%) there were a total of 8 rain/runoff events, showing that runoff is a rather common event in hilly conditions.
In the vineyard used in this study by our farm, only 1 runoff event was recorded between August 28-31, 2020, after a very heavy downpour: the maximum intensity was 9.2 mm/5 min, and the total rainfall was 136 mm. It is important to stress that the vineyard studied is not very prone to runoff because the slope is slight and the soil is rich in sand and organic material, so only extreme precipitation could cause significant runoff.