Microlysimeters to Measure the Water Use of Seedling Cotton

Information on water use of cotton, from planting to squaring, is limited. Part of the problem is that the measurement of water use is difficult given the small size of the cotton plant and the lack of soil and plant based sensors available to measure crop water use. Thus the objective of this research was to design a weighable lysimeter to measure the water use of cotton in the early stages of crop growth and under field conditions. For this purpose, cylindrical lysimeters (15 cm x 35 cm) were built and weighed using load-cells. This design was selected because this size would allow for a couple of plants to grow to first square, yet small enough to be weighed by a single load cell. Lysimeters were placed in the field after planting, prior to cotton emergence before the first week of the experiment. Beginning each week of the study, a set of 16 lysimeters (8 bare soil, 8 containing cotton) were randomly chosen and extracted from the soil. The MLs were then capped on the bottom and placed into individual holes dug into the soil on top of load cells. The soil holes were cased with pipe for ease of measurement. Each subsequent week of the study, 16 new MLs were extracted from the soil until all MLs were used. Daily changes in microlysimeter mass were measured, and the change in mass was converted to depth (mm) of water loss. Cotton seedling transpiration was measured as the difference in water loss between the planted and bare soil MLs. Ancillary measurements taken during the study included were: soil and ML temperature, LAI, soil water content and local weather data for reference crop evapotranspiration.