Effects of greywater irrigation on germination, growth and photosynthetic characteristics in selected African leafy vegetables

E Lubbe,Sershen Naidoo,N Rodda

doi:10.4314/wsa.v42i2.04

Abstract

The reuse of greywater, wastewater from sources other than toilets, could enable low-income households to save potable water for drinking and cooking. Greywater irrigation of food crops is widely practised but its effects on African leafy vegetables (ALVs), which hold potential for cultivation to improve food security, are unknown. This study investigated the effects of synthetic greywater irrigation on germination in three ALVs, viz., Amaranthus dubius, Cleome gynandra and Solanum nigrum, and subsequent seedling growth in A. dubius and S. nigrum. Seeds and seedlings were treated with chlorinated and dechlorinated greywater and tap water, supplemented with nutrients. Greywater application decreased germination capacity (by 23–25%) when assessed in Petri dishes in A. dubius only. However, greywater application was less harmful to A. dubius seeds sown in soil. Vigour was compromised in greywater-treated seeds of all three species but greywater can be used to irrigate freshly-sown seeds of A. dubius without reducing percentage seedling production. However, greywater irrigation reduced capacity (by 21–23%) and rate of shoot emergence in S. nigrum, and growth and chlorophyll content in both species. These negative effects were accompanied by increased soil electrical conductivity (after 21 d) and pH (after 14 d). The reduced growth under greywater irrigation was most likely based on a reduction in light-harvesting capacity and/or nutrient availability. Overall, S. nigrum seedlings were significantly more sensitive to the negative effects of greywater, possibly due to increased transpirational water loss under greywater irrigation. The effects of greywater were largely independent of chlorine content. Applying greywater in excess of plant requirements and/or alternating greywater irrigation events with freshwater watering events could promote leaching of salts found in greywater. The effects of greywater irrigation on soil water and nutrient availability demand further investigation for ALVs.Keywords: African leafy vegetables, greywater irrigation, germination, seedling growth

Highlights

The number of people living in either water-stressed or waterscarce countries is expected to reach 3 billion by 2025 (Hanjra and Qureshi, 2010)
The present study investigated the effects of greywater irrigation on seed germination capacity and velocity in A. dubius, C. gynandra, and S. nigrum
In S. nigrum, the Seed Vigour Index (SVI) for greywater treatments was relatively lower but these differences were only significant between dechlorinated greywater (DGW) and the two tap-water treatments (p < 0.01)

Summary

Introduction

The number of people living in either water-stressed or waterscarce countries is expected to reach 3 billion by 2025 (Hanjra and Qureshi, 2010). Innovative approaches are needed to attain both water and food security, in subSaharan Africa (Finley et al, 2009; Hanjra and Qureshi, 2010; Rodda et al, 2011). Greywater could be useful for irrigation of subsistence crops such as African leafy vegetables (ALVs), which are consumed across Africa (Van Rensburg et Received: 17 May 2015; accepted in revised form 22 February 2016 al., 2007); its effects on germination and seedling growth in these species are presently unknown. Ex Thellung., Cleome gynandra L., and Solanum nigrum L., which have the potential to become cultivated species (Van Rensburg et al, 2007) This will greatly increase their availability in the face of impending water and food insecurity

Methods

Results

Conclusion