Abstract
The role of crop canopies in the global water cycle is a topic of increasing international interest. How much rain and sprinkler-irrigation water are returned to the atmosphere or reach the soils beneath crop canopies, and the pathways of those water inputs at the soil, are linked to agricultural productivity and sustainability. This concise-format review synthesized and evaluated the available, limited, observational data (138 studies) on cropland throughfall, stemflow, and/or interception for >60 crop species covering all major climate types to obtain a global analysis of rainfall and sprinkler-irrigation partitioning by crop canopies. Partitions normalized per unit rain/sprinkler-irrigation (relative fractions, %) vary greatly across crop types with the interquartile range of throughfall, stemflow, and interception being 58–83%, 2–26%, and 11–32%, respectively. Stemflow data distribution across crop types is more often different than for throughfall and interception, contributing to overall variations in the partitioning of rain and irrigation observed to date. Partitions per storm also differ depending on the magnitude of rain or sprinkler-irrigation events and the stage of crop growth. Furthermore, throughfall and stemflow input patterns at the soil surface and subsurface may erode soils through different physical processes (i.e., throughfall droplet impact/splash versus scouring by stemflow); however, more research is needed to elucidate the underlying mechanisms and overall impacts. Finally, comparative analyses of partitions among croplands, shrublands, and forests indicate that crop canopies partition rain inputs differently and that there is a lack of studies in croplands. Hence, we suggest that future effort should be directed to the partitioning of rainfall and sprinkler-irrigation by canopies in agricultural settings.
Highlights
Global crop production and its connection to water resources are foundational to human well-being
Understanding rainfall and sprinkler-irrigation partitioning patterns and variations in croplands may be relevant to global crop productivity and sustainability, as well as water resource management, especially given current global climate change projections
Croplands have had the highest proportion of water input becoming recharge, compared to grasslands, woodlands, and scrublands [86]; study on the ecohydrological processes of cropland ecosystems that control the amount of water inputs to the surface is merited
Summary
Global crop production and its connection to water resources are foundational to human well-being. Over the past 150 years, modeling frameworks for the partitioning of rainfall into interception, throughfall, and stemflow have been primarily based on observational studies in forests and shrublands [9,10,11,12]. This is problematic as plant canopy structure in agricultural settings differs markedly from forests and shrublands, especially for herbaceous crops; croplands are expected to partition rainfall and sprinkler-irrigation waters differently. This article is a condensed review of 138 studies reporting these observations to date, to (i) discuss the relevance of these synthesis and comparative results to surface (i.e., soil erosion) and subsurface processes (i.e., soil moisture) in croplands, (ii) compare these observations to several hundred forest and shrubland studies recently synthesized [9], and (iii) identify current knowledge gaps and suggest future directions for rainfall and irrigation partitioning research in cropland ecosystems
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