Allelopathic influences of organic and bio-dynamic treatments on yield and quality of wheat and potatoes

Abstract

Keywords: allelopathy, biodynamic, organic, quality, sustainability, silicon. To verify the effectiveness of an established set of agricultural techniques involving application of natural solutions and extracts, crop rotations and associations - here collectively designated as Applied Allelopathy; a sequence of field, glasshouse and laboratory experiments was carried out from 1993 to 1997. Two test crops of world importance - wheat and potatoes, were chosen to provide responses from both a Mono and a Dicotyledon with physiologically different growing habits and end products (grains, tubers). The following treatments were tested: 1. Field sprays - used in sequence and additional to compost treatments: P500 soil spray (fermented cow manure), P501 plant spray (ground quartz), Nettle aqueous extract (Urtica dioica - planta tota), Equisetum axvense decoction and Kieselguhr (diatomaceous earth) suspension. 2. Compost additives P502 to P507 (200 mg.m-3) : Achilea millefolium - flowers, Matricaria recutita - flowers, Urtica dioica-planta tota, Quercus robur - bark, Taraxacum officinale - flowers and Valeriana officinalis - flowers' liquid extract. 3. Rotations with a Rye-Vetch mixture for assessment on crop responses and weed suppression through green manuring and mulching. The specific objective is to identify whether and/or which of the biodynamic preparations, organic and mineral extracts and rotations with weed suppressing green manures, do have allelopathic effects on the yield and quality (e.g., baking and storage properties) of wheat and potatoes. A general objective is to develop and test an integrated set of simple methodological designs that can combine systems (holistic) and analytical approaches, built upon a coherent critical philosophical-scientific foundation. Although the main scope of this research work is on the Agronomic aspects and results, some indications of the underlying physiological and biochemical mechanisms involved in the obtained results are given. Consecutive series of randomised complete block design (split-plots and factorials) field and glasshouse trials were carried out as blind-coded experiments, comparing Control, NPK, Organic and Biodynamic compost soil treatments, combined with field sprays and extracts in different dilutions. Results were based on field assessment of growth, biomass, weeds and yields; storage and laboratory analysis of quality parameters such as thousand grain weight (wheat TGW), Hagberg Falling Number (wheat HFN), dry matter and mineral contents, storage losses, grading and tissue browning (potatoes). The method of Selected Orthogonal Contrasts for partitioning the treatment sums of squares was used to allow specific comparisons between treatments. Significant differences using the F-test, were found both for the interaction of soil treatments and sprays overall in the field experiments and for several comparisons involving individual treatments and dilutions. The BD and organic systems offered significant positive differences in relation to the nil control, in terms of both yields (for both wheat and potatoes) and quality. This was expressed especially in the lower potato storage tissue browning and its resulting higher net amount of good marketable tubers, but also in the ideal wheat baking quality achieved by the BD treatment. Organic and BD yield increases did affect quality parameters like wheat TGW and potato DM%, which remained as high as in the control. They also did not cause any significantly different increase in soil nitrate and ammonium, actually displaying the same levels of these compounds as the control in the soil analysis results.The agrochemical treatment (Nitram for wheat, NPK for potatoes) produced significantly higher yields only in the wheat trials, but offered significantly lower values of wheat TGW and potato DM%, and very significantly increased soil nitrate levels in the soil, even after harvest time. The BD and organic systems did not differ in general in terms of yields, although there were trials like potato'93 in which the organic yielded significantly less than the agrochemical treatment, while the BD did not. It was in terms of both wheat and potato quality that the BD treatment system showed the following significant advantages, even over the comparatively equivalent organic system: • Ideal wheat flour baking quality (HFN, well-balanced alpha-amylase activity). • Significantly less potato tuber pest field damage and storage losses by tissue browning. Biodynamic and allelopathic sprays, like silica P501 and nettle water (Urtica dioica), can significantly improve yields and quality of both potatoes and wheat. However, their general mode of action can be defined as regulatory or "normalising", considering that when over-applied at near optimum crop conditions, they can reduce yields and negatively affect quality parameters. A green manure rotation and mulch like the rye plus vetch mix used in Experiments Three and Four (1994) can have significant effects, either beneficial (build-up of soil organic matter and weed suppression) or detrimental (allomonic action of allelochemicals present in the plant residues) on the subsequent crops. Silicon (Si) based sprays produced interesting results in the 1995 wheat and potato split-plot field trials, especially P501 in the interaction with the BD soil treatment system, which offered a significant opposite interaction response in relation to the other three systems. This phenomenon was expressed in the following results: • The DGA biomass samples of wheat, potato plants and weeds, which showed significantly contrasting growth curves and sample DWts between P501 and the water control spray. • While P501 increased the HFN in the BD system, it decreased HFN values in the other three systems. • While P501 sharply decreased total and ware potato yields in the BD system, it increased them in the other three systems. The opposite contrast occurred in relation to potato 'chat' yields, which increased in the BD system, while decreasing it in the other three systems. • P501 also increased the amount of storage browning in tubers from the BD system, while decreasing it in the other three systems. These results and the fact that the BD treatment system produced significantly contrasting results in relation to the other systems for most of the interactions observed, including the analytical approach field trials, support the hypothesis of a regulating or normalising effect of the BD preparations. They generally increase yields and improve quality under sub-optimal conditions, but cause limitations whenever applied beyond these optimum levels for specific parameters (Spiess, 1979; Raupp & Konig, 1996).