Why Maize Sometimes Behaves Like Pine: Throughfall Microstructure and LAI Influence

When vegetation intercepts precipitation, the quantity of rainwater reaching the ground is affected, as it passes through the canopy, drips from it, and runs down the stem. Interception also significantly alters the characteristics of rainfall, which is among others reflected in differences in the number, size and velocity of raindrops. Throughfall drop size distribution was monitored and analysed for three vegetation types, including a single pine tree in an urban park, trees in an urban mixed forest, and a maize field in an agricultural area. Velocity-diameter diagrams were compiled for the 33 selected throughfall events and grouped into three distinct clusters based on similarity using a hierarchical clustering approach. Pine throughfall events were grouped in Cluster 1, urban mixed forest events in Cluster 2, while maize events were split between Clusters 1 (with all the pine tree events) and Cluster 3. A detailed analysis of rainfall microstructure characteristics under maize and pine canopies was conducted in relation to the rainfall event conditions and crop growing stage to evaluate why, in some cases, throughfall microstructure under maize is similar to that beneath pine (events assigned to Cluster 1), and, in other cases, it differs (events assigned to Cluster 3). Throughfall events in Cluster 3 were generally larger and more intense, showing a unimodal temporal distribution. In contrast, maize throughfall events in Cluster 1 exhibited a bimodal distribution, with two intensity peaks separated by a rainfall break. Notably, the maize leaf area index (LAI) exceeded a value of 4 during the period when the shift occurred from the events assigned in Cluster 1 to the subsequent events assigned in Cluster 3. As maize leaves mature, they become less flexible and do not bend as much under the weight of rain. Consequently, throughfall consist of more drips (larger drops) than direct rainfall (smaller drops). Further research could include additional types of vegetation, and the results could be supported by measurements over a longer period of time. These values could also be used for direct analyses of rainfall erosivity.

Acknowledgment: This contribution is part of the ongoing research project entitled “Evaluation of the impact of rainfall interception on soil erosion” supported by the Slovenian Research and Innovation Agency (J2-4489) and the Austrian Science Fund (FWF) I 6254-N.