Logo: to the web site of Uppsala University

This study was made within the Management of Acid Sulphate Soils (MASS) project and was carried out at Tan Thanh Experimental Farm.

A large part of the Vietnamese Mekong Delta consists of acid sulphate soils. The acidity causes chemical, as well as biological and physical problems for agriculture. Farmers of the Mekong Delta have in some ways overcome the disadvantages with acidity. Inappropriate strategies may on the other hand lead to further acidification. A physical and a chemical model have been developed within the MASS Project in the aim to find profitable water management methods. In this study some parameters of the soil were studied to obtain data for the models. The aim was also to study the reliability of the performed measuring methods in acid sulphate soils.

The infiltration capacity was measured with a double ring infiltrometer. The infiltration capacity showed large variations, ranging from 3 to 281 mm h^-1. The medium capacity in a drained field was 102 mm h^-1, in a uncultivated field 35 mm h^-1 and in another cultivated, not drained, field 62 mm h^-1. 

Tidal movements from a canal into a field was studied to determine the horizontal transmissivity. The groundwater movement was studied using nine observation tubes along one field. Tidal effects on groundwater could be seen in the tubes as far as 50 m from the canal, but also the evaporation affected the groundwater level. The measured average transmissivity was 15 m²day^-1 which is probably overestimated. The specific storage coefficient in the field was 0.08. The soil cracks during drainage. Those cracks were the reason for the high infiltration capacity.

Further infiltration measurements should be carried on during the period of irrigation. The transmissivity could not be determined by this method, at least not with the observation tubes too far from the canal. Other methods should be used, or the observation tubes should be placed closer to the canal, 0 to 5 metres.