Tillage erosion is the soil movement and erosion by tilling a given plot of land. Tilling every other year is called rotational tillage. Only light pruning and occasional tilling to reduce weeds is necessary. In traditional agricultural systems, tilling disturbs the soil ecosystem, affecting biotic and abiotic factors. This also helps prevent soil loss by avoiding erosion after tilling. One of the purposes of tilling is to remove weeds. Very few people were engaged in tilling the soil on account of wars. They all praised the virtues of a life devoted to the tilling of the soil. Spanish farmers also introduced tilling and irrigation to the land, further changing the landscape. The helots were used as unskilled serfs, tilling Spartan land. Oftentimes this may include tasks such as tilling land, grinding grain, carrying water and cooking. Another theory associates Varaha with tilling of the land for agriculture. Recent improvements to drills allow seed-drilling without prior tilling. They believed that bottom trawling, like tilling of land, actually increased production. They would receive payment in clearing and tilling the first two acres.