Deep plowing is a plowing to a depth greater than 50 cm (20 in) as compared to ordinary plowing which rarely exceeds 20 cm (8 in).[1] The purpose of deep plowing is to modify the soil water retention characteristics over the long term.[1] In one long-term test, lasting 35 years, the mean annual grain yield was 2,800 lbs per acre (3,138 kg per ha) with deep plowing, which was 10% greater than the 2,550 lbs per acre (2,858 kg per ha) yield in unplowed plots.[1]
Under certain conditions, it is recommended to use deep plowing in preparing the soil for planting new vineyards.[2]
There is a movement away from plowing altogether and from deep plowing in particular.[3] The theory is that this will stop the loss of topsoil, increase the organic content of soil and reduce runoff of fertilizer and pesticides into rivers.[3] Another part of the no-plowing theory is that ground moisture would be conserved; but this was shown to be incorrect by a 35-year study.[1]