Role of Canopy Coverage in Water Use Efficiency of Lowland Rice in Early Growth Period in Semi-Arid Region

Tetsuji Suzuki,Osmund Mwandemele,Jun-Ichi Sakagami,Yasuhiro Izumi,Morio Iijima,Koji Yamane,Luke Kanyomeka,Takeshi Ohta

doi:10.1626/pps.16.12

Abstract

An appropriate combination of rice cultivar and cropping system that maximizes water use efficiency (WUE) may improve yield of rainfed lowland rice. In the paddy field, a large amount of water is consumed by evaporation during the early growth period, and it can be reduced by canopy coverage especially in semi-arid regions. Therefore, we evaluated the role of canopy coverage in WUE of rice in the early growth period in semi-arid region. A pot experiment was conducted in Namibia to investigate the genotypic and species difference in WUE, and another pot and a field experiment were conducted to investigate the effects of planting density on WUE. Although no significant difference was observed among species, the mean WUE was in the decreasing order of Oryza sativa, and Oryza glaberrima followed by the interspecific progenies including NERICA. In contrast, there was a significant difference in WUE at the genotypic level. Highly tillering genotypes such as WAB1159-2-12-11-5-1 and WITA 2 showed a high WUE. Furthermore, WUE was significantly correlated with the number of tillers (R2 = 0.453), and higher planting density resulted in a higher WUE. In contrast, stomatal conductance had no significant correlation with WUE (R2 = 0.081). Thus, the physical conditions affected by number of tillers and planting density had greater impacts on WUE than physiological characteristics such as stomatal conductance. The suppression of surface water evaporation by coverage was significant, probably contributing to WUE improvement. To increase WUE in semi-arid regions, we recommend the increase of canopy coverage and higher planting density.

Highlights

More than 30% of the global rice cropping area is rainfed lowland (IRRI, 2010) and irrigation systems are often too expensive to implement (Becker and Johnson, 2001)
S&P is a major component in water loss, we focused on the suppression of surface water evaporation to achieve a high water use efficiency (WUE) in this study because a large amount of water loss occurs during the early growth period by surface water evaporation (Adachi et al, 1995; Cabangon et al, 2002)
No significant difference was observed among species, the mean WUE was in the decreasing order of Oryza sativa and Oryza glaberrima followed by interspecific progenies including NERICA

Summary

Introduction

More than 30% of the global rice cropping area is rainfed lowland (IRRI, 2010) and irrigation systems are often too expensive to implement (Becker and Johnson, 2001). The direct seeding technique has been proposed to reduce water loss by shortening the land preparation period (Cabangon et al, 2002), but this technique is not always applicable in rainfed paddy fields in semi-arid regions. The increase of canopy coverage may help suppress surface water evaporation in rainfed paddy fields. The increase of canopy coverage can be an effective method to improve WUE in rainfed paddy field in such regions. There are few if any field studies conducted in semi-arid regions that take into account the role of canopy coverage in WUE of rice. Transplanting of large plants with a high planting density might improve WUE of rice by suppressing surface water evaporation. We hypothesized that the increase of canopy coverage would reduce surface water evaporation and improve WUE of rice in semi-arid regions. We investigated the effects of planting density on WUE in pot and field experiment since planting density substantially affected canopy coverage, and we discuss the role of canopy coverage in WUE of rice

Methods

Results

Conclusion