Chinampas, Aztec agriculture employed chinampas for their harvests at the empire's center. Chinampa is a farming technique that employs small, rectangular plots to cultivate crops on the shallow lake bottoms of Mexico's valley. These islands then provided fertile soil and easy access to water for agriculture. The use of chinampas for agricultural purposes represents an important contribution to the development of New Spain (Mexico). Before this innovation, Spanish farmers had only been able to rely on natural fertility of the soil or large-scale irrigation projects for successful cultivation. The introduction of this new technology allowed them to have two harvest seasons per year instead of one, which greatly increased food production for the colony. This form of agriculture was very labor-intensive, so it was not appropriate for large-scale production. Also, the islands could not support much weight, so most crops were grown in floating platforms called tablas de palma. These were usually made out of wood and dragged across the lake bed to where they would be needed when ready for harvesting. There are still many lakes in Mexico that employ this method of agriculture today. The system had its drawbacks though. It was difficult to transport goods on or across the islands, so trade within the colony was limited. It also meant that if one part of the island became depleted of crops, it would need to be replaced with more expensive land farther from the center.