REPOSITORY > RESULTS

Abstract

Due to increasing food demands, an improvement in the growth of food crops is desired as a mechanism of increasing yields. At the same time, agricultural sustainability should be achieved to meet these food demands without harmful environmental effect. To this end, highly reactive plasma technologies have been introduced to agricultural research as “plasma agriculture”. These environmentally benign alternatives to chemical-based approaches show promise regarding germination, growth and yield stimulation of various crops.
In this dissertation, we have studied the effects of inductively coupled, low-pressure radio frequency oxygen plasma on garlic cloves. Specifically, we worked with a Slovenian autochthonous garlic cultivar (Ptujski spomladanski) with the aim of boosting garlic growth, strengthening the plant, and improving its yield, while maintaining an ecologically friendly approach.
To treat the cloves, we have used pilot-scale and industrial-scale plasma reactors at a variety of treatment conditions. We have characterized the employed discharges using OES and a catalytic probe, as well as evaluated the effect of plasma treatment on the clove temperature. The physico-chemical and biological responses of unpeeled and peeled cloves differed due to the shielding function of the protective leaf, as well as differences in surface chemistry and biological function.
The effect of oxygen plasma on the surface properties of cloves was substantial. We have analyzed changes in the surface chemistry using XPS and ATR-FTIR. The plasma treatment increased the surface oxygen content and the O/C ratio through progressive oxidation of cuticular waxes, brought upon by functionalization mechanisms. At the same time, minor elements appeared at the surface in low amounts, indicating their exposure from deeper layers due to chemical etching of the cuticle. Surface morphology modification was evident in SEM and AFM images. In particular, with increasing oxygen atom dose, plasma treatment progressively etched the surface of the protective leaf. Conversely, protruding waxy structures appeared at the surface of plasma-treated peeled cloves, suggesting surface restructuring. The combined effect of changes to surface chemistry and morphology was increased wettability, indicated by WCA measurements, as well as improved water uptake.
Plasma treatment also affected the biological response of the cloves. During laboratory growth, treatment at suitable conditions increased sprout length, root length, and/or root number. These improvements translated into yield increases in field growth experiments, as indicated by higher mean dried bulb mass compared to garlic grown from untreated cloves. Further, the achieved yield improvements persisted into the second and third generation of garlic without the need for additional treatment.
Our findings show that at suitable plasma treatment conditions, garlic sprout and root growth is stimulated. Using properly tuned discharge parameters, plasma treatment can be a useful agricultural tool for stimulation of garlic germination and improvement of its yields.