Measuring soil infiltrationrates in cultivated land : A case study of Ifakara, Tanzania

Abstract: An increased global food demand requires an increase in agricultural land use, which in turn affects the hydrologic cycle. A central process in this regard is infiltration of rainfall through the land surface. While there are standard values available for different soil types, land cover also has a documented influence on infiltration rates. This makes infiltration highly variable acrosss patiotemporal scales and as such, difficult to measure in field, thus selection of an appropriate measurement technique is important to consider. Therefore, this study aimed to establish a method for robust infiltration measurements and compare rates from various crops (rice andmaize) and soils (sand and clay) to see if there is consistency between physical controls on infiltration and farming practices. The study area is located near the town of Ifakara in south-central Tanzania. Data were gathered during eight weeks (October- November) using variousring infiltrometer set-ups. The results from 12 comparative infiltration measurements indicated that a smaller ring implies less measurement precision. Precision was improved by using a doublering setup and/or a larger single ring. Infiltration measurements from the nine agricultural fields corresponded well to estimations from the Horton infiltration equation (correlation coefficient >0.98). The results from all 36 measurements indicated a statistically significant difference between crop types as well as between soil types. The significance was, however, higher for soils compared to crops. Part of the inconsistency of infiltration rates could be explained by the cultural factor where traditions are important for crop choice and farming. Further, the measured infiltration confirmed the large spatial variations of infiltration rates both within and across fields, with implications for large scale agricultural development.