The Song government provided tax incentives to farmers who tilled lands along the edges of lakes, marshes, seas, and terraced mountain slopes. Farming was made possible in these difficult terrains due to improvements in damming techniques and using chain pumps to elevate water to higher irrigation planes. The 10th century introduction of early-ripening rice that could grow in varied climatic zones and topographic conditions allowed for a significantly large migration from the most productive lands that had been farmed for centuries into previously uninhabited areas in the surrounding hinterland of the Yangzi Valley and Southeast China, which experienced rapid development. The widespread cultivation of rice in China necessitated new trends of labor and agricultural techniques. An effective yield from rice paddies required careful transplanting of rows of rice seedlings, sufficient weeding, maintenance of water levels, and draining of fields for harvest. Planting and weeding often required a dirty day of work, since the farmers had to wade through the muddy water of the rice paddies on bare feet. For other crops, water buffalos were used as draft animals for ploughing and harrowing the fields, while properly aged and mixed compost and manure was constantly spread.