The development of better site preparation techniques made the biggest impact on the development of forestry practice in Scotland. By 1929 turf planting had been adopted in every district on the peat types suitable for forestry. However, the method of turf planting had some basic problems because it was very labour intensive, it did not improve drainage sufficiently, and it was not deep enough to break through podzolic iron pans. It was realised that if the land could be ploughed it would solve these problems and make it possible to cultivate upland moors and plant them economically. In 1927 the first attempts were made to pull a plough by horses, but these experiments were not very successful. The horses were not strong enough to turn the tough peat and the ploughs were not heavy enough to break the iron pan.