Applicability of subirrigation in clayey paddy fields converted to upland fields.

Abstract

To determine the applicability of subirrigation in clayey paddy fields converted to upland fields, water movement during subirrigation and the effect of subirrigation on wheat yields were investigated in field tests. Subirrigation supplies water to drain pipes by gravity from the irrigation canals. The results were : ① Where the subsoil had well-formed cracks, irrigation water flowed laterally in the subsoil through the cracks, and penetrated the plowed layer by gravity from the subsoil near the drain pipes after the cracks in the subsoil were filled. ② When supplying irrigation water up to the plowed in this manner, it was necessary to pay attention to the ability of crop to endure wet conditions as the plowed was extremely wet for some time even when drainage took place after irrigation. Supplying water only to subsoil with roots growing in cracks, not up to the plowed layar, was found to be suitable for wheat. ③ Little leakage of irrigation water and high permeability in the subsoil by well-formed cracks were necessary to use subirrigation. However, it is difficult to establish objective criteria that will determine fields which satisfy these requirements.