Tobacco

Effect of Terra Dynamics humic substances on tobacco leaf anatomy

J. Peacock (Terra Dynamics (Pty) Ltd),
J.W. Swanepoel (University of Pretoria)
C.F. van der Merwe (Potchefstroom University for CHE)

September_02a Humic substances are very important soil constituents. Together with soil clays, the humic substances are responsible for many chemical activities in soils. They enter in complex reactions and may influence the growth of plants indirectly and directly (Tan 1993). Vaughan (1974) made the hypothesis that the enhanced growth of plants with the application of humic substances is due to an increase in the size of the cells, as opposed to an increase in the number of cells. This enlargement involves a stretching or a loosening of the wall already present, as well as the synthesis of new wall materials (Cleland 1971). The aim of this study was to determine whether the humic substances, namely fulvic acid and humic acid could improve tobacco quality and yield. The plants treated with humic substances also received additional calcium as Rihouey et al. (1995) found that if the calcium load in the cell wall area is too low, calcium bridge formation is not possible. The mechanism of interaction of calcium is directly related to the chemical structure of pectins (Rinaudo 1989). Two important characteristics that the farmer requires for optimal tobacco yields are thin but heavy leaves.

The control tobacco (Nicotiana tabacum L.) plants received the normal fertilizer program while the treated plants received humic substances and 60kg/ha calcium additionally. Leaf pieces of 25mm₂ were cut from the middle of the leaf lamina and weighed. Anatomical data was quantified with the aid of a Flexible Image Processing System (FIPS) using light microscopy. Scanning electron microscopy was used to verify this information. The cell walls are also studied with FESEM to determine whether there is any difference in cell wall ultrastructure.

September_02b Tobacco leaves obtained from plants treated with humic substances revealed anatomical differences from that of the control. The leaves of the treated plants were found to be ca. 18µm (Fig. 1 and 2) thinner than the control leaves. The percentage intercellular spaces were 25% less for the tobacco plants treated with humic substances (Fig. 1 and 2). The advantage of smaller percentage intercellular spaces is that it contributes to the drought tolerance of tobacco plants (Van Rensburg et al. 1994) which is an advantage for the farmer in dry warm seasons. Leaf pieces weighed ca. 2mg more for the treated plants than the control. This result could mean higher yields per hectare for the farmer. The tobacco plants treated with humic substances also revealed ca. 10 palisade parenchyma cells more per leaf surface area than the control. This could explain why the thinner leaves weighed more than the thicker leaves together with the fact that it has a smaller percentage intercellular spaces per leaf area.

To conclude, humic substances do result in thin, but heavy leaves for optimal tobacco yield.

References

Cleland, R.E. (1981) Ann.R.Plant Physl. 22, 197.Rihouey, C., Jauneau, A., Cabin-Flaman, A., Demarty, M. Lefébvre, F. & Morvan, C. (1995) Plant Physiol. Biochem. 33, 497. Rinaudo, M. (1989) In: N.G. Lewis & M.G. Paice, ed. Plant Cell Wall Polymers, Biogenesis and Biodegradation. American Chemical Society, Washington, 324. Tan, K.H. (1993) Principles of Soil Chemistry. Marcel Dekker, Inc., New York, 83. Van Rensburg, L., Kruger, H. & Kruger, G.H.J. (1994) S.Afr.J.Bot. 60, 227. Vaughan, D. (1974) Soil Biol. B. 6, 241

Terra Dynamics Humiensuur en Kalsium vir tabak

Figuur A: Krimping van selstrukture met voorbereiding vir die SEM.

Daar is nuwe resultate van die Vaalwater tabakproef wat 6 Desember 1999 geplant is en waarna verwys is in die vorige twee Terra Dynamics Nuusbriewe.

Met behulp van 'n skandeerelektronmikroskoop (SEM) is die tabakblaar se selle 'n 1000 keer vergroot. Die resultate toon dat die sponsparenchiemselle van die kontrole (Fig. A) gekrimp het teenoor die behandeling wat Terra Hume asook 60kg Ca addisioneel ontvang het.

Figuur B: Baie min krimping van selstrukture met voorbereiding vir die SEM.

Kalsium speel 'n belangrike rol in die struktuur van plante se selwande en indien voldoende kalsium nie teenwoordig is sal die struktuur swak wees (Rihouey et al. 1995 en Rinaudo 1989) en krimping sal plaasvind soos in figuur A met die voorbereiding van die materiaal vir SEM.

Verdere studies word voortgesit aangesien die resultate ook van groot belang is vir rakleeftyd van vrugte en groente.

Ekonomiese analise van tabakresultate

Die tabakboer bevind homself in 'n benarde knyptang posisie met 'n tipiese totale insetkoste huidiglik konserwatief geraam op R25 000 per hektaar. Dit teenoor 'n verwagte inkomste van slegs R22-24 000 per hektaar. (Bereken teen die huidige verwagte verkoopprys rondom R10.00 per kilogram en geraamde opbrengs van 2200 to 2 400 kilogram per hektaar).

Tydens die proef op Vaalwater, waarvan die resultate gerapporteer word hier en in die vorige twee nuusbriewe, is 'n 25% hoër opbrengs verkry (2 400 kg/ha teenoor 3 000 kg/ha). Die produk insetkostes van die Terra Dynamics humiensuur, fulviensuur en kalsium produkte was slegs R1 340.00 per hektaar of te wel 5,4% van die tipiese totale insetkoste.

In die Potgietersrus omgewing het 'n Terra Dynamics kliënt sy gereelde 2 200 kg/ha met 32% opgeskuif na 'n gemiddelde 2 900 kg/ha.

Teen die huidige verwagte verkoopprys van rondom R10.00 per kilogram vertaal dit na 'n opbrengs van R6 -7 000 op 'n belegging van R1 340.00 per hektaar.

Terra Dynamics en sy kliënte is oortuig daarvan dat die bestuur van koolstof in die grond (bestuur van grond organiese inhoud) 'n kragtige instrument is om die ys te breek en die raamwerk te skep om insetkoste af te bestuur en inkomste merkbaar te verhoog.

Die opheffing van grondstruktuur probleme met Terra Dynamics se kaliumhumate kan duidelik waargeneem word.

Die grond het 24% slik en 21,4% klei in, en slegs 12,5% stabiele korrels groter as 0,25mm. Met 0,08 massa % kaliumhumaat is die hoeveelheid korrels groter as 0.25mm verhoog na 23,5%.