Solar yam stakes increase yield

Though leaves of conventionally grown staked yam vines often appear green and healthy, there is yellowing or browning of large numbers of hidden inner leaves on the stake/trellis.

However, researchers from the Mandeville-based Northern Caribbean University (NCU) have demonstrated a novel technique using artificial stakes to decrease leaf deterioration as well as increase crop yields. The technique also potentially reduces deforestation and the threat to biodiversity caused by the cutting down of an estimated 10 million saplings per annum across Jamaica for yam stakes.

The research team comprises Dr Mark Harris, professor of environmental chemistry and environmental science; Charles Koomson, graduate researcher; and Lemore Jones, assistant professor. Their findings, titled A Solar Vine-support System for Yam Cultivation, have been submitted to the journal Tropical Science.

Construction

To offset the demand for yam stakes and decrease deforestation, extracting maximum yields in a sustainable way is essential. Normally, three or four yam vines planted around a vertical guide stake produce a 'cylinder', or canopy of leaves, which bathes inner leaves with a dense shade. In this manner, leaves change the composition of light by filtering out the more photosynthetically active wavelengths. The plastic yam stake concept in itself is not new.

However, by attaching a 60cm x 38mm round plastic pipe as perpendicular 'branches' in the shape of north-south and east-west directions into orifices previously made at 30cm intervals into a 2.5m-high rain guttering downspout drain pipe of 10cm square cross section, the NCU researchers doubled the radius of a conventionally staked canopy.

This design trebled what would be the cylindrical area occupied by leaves, thereby diluting the dense interior shade. Further, the extra length of circumference provided to some leaves meant a longer time spent in the brightest light available to the canopy. As a result, leaf longevity was increased. It is hence referred to here as a solar yam stake.

Growth and harvest

All vines were equally irrigated. After just eight months, the solar staked yams produced higher tuber weights than conventionally staked by approximately 30 per cent. The solar stakes also proved to be reusable. Cross-sectional observations of the canopy revealed that the vines supported by the solar stakes had no yellow leaves at any stage during the growth period. In contrast, conventional stakes showed some yellow or brown inner leaves at all stages.

At harvest, scores of green, photosynthesising leaves were observed on strong, greenish vines of 75 per cent of the branched yam stakes. Further, because leaf size decreased in the interior of the canopy, the solar stake contained more large leaves, as it had a wider diameter than that of the conventional stake.

In contrast, leaves and vines on 75 per cent of conventional stakes were in a shrivelled, brown and dry state. This implies that, had the harvest occurred a month later at maturity, the differences in yield would have been even greater. The explanation for the green leaves on the solar stakes were (a) increased light penetration, which reduced leaf mortality and improved photosynthesis; (b) possibly the facilitation of greater air diffusion inside the canopy; and (c) less intense shade in the interior.

Exposing the inner leaves of the yam canopy to improved ambient conditions substantially increased tuber weight. The impact of the weather on the solar stakes was minimal, and they are currently being used a second time. Based on the known durability of the materials used in this study, the researchers predict a usable life of at least 10 years for the solar yam stakes.

As a single conventional yam stake costs $50-$100, and on yam farms, there are approximately 3,000 per acre, solar stakes promise significant benefits not only to farmers and food production, but to the fragile environments such as the Cockpit Country and other ecosystems currently being inexorably deforested to supply large quantities of traditional yam stakes.