Abstract
Organic Amendments (OAs) has been used in agroecosystems to promote plant growth and control diseases caused by soilborne pathogens. However, the role of OAs chemistry and decomposition time on plant growth promotion and disease suppression is still poorly explored. In this work, we studied the effect of 14 OAs at four decomposition ages (3, 30, 100, and 300 days) on the plant—pathogen system Lactuca sativa–Rhizoctonia solani. OAs chemistry was characterized via 13C-CPMAS NMR spectroscopy as well as for standard chemical (i.e. N content, pH, EC) and biological parameters (i.e. phytotoxicity and R. solani proliferation bioassay). OAs have shown variable effects, ranging from inhibition to stimulation of Lactuca sativa and Lepidium sativum growth. We recorded that N rich OAs with high decomposability were conducive in the short-term, while converting suppressive in the long term (300 days). On the other hand, cellulose-rich OAs with high C/N ratio impaired L. sativa growth but were more consistent in providing protection from damping-off, although this property has significantly shifted during decomposition time. These results, for the first time, highlight a consistent trade-off between plant growth promotion and disease control capability of OAs. Finally, we found that OAs effects on growth promotion and disease protection can be hardly predictable based on the chemical characteristic, although N content and some 13C CPMAS NMR regions (alkyl C, methoxyl C, and carbonyl C) showed some significant correlations. Therefore, further investigations are needed to identify the mechanism(s) behind the observed suppressive and conducive effects and to identify OAs types and application timing that optimize plant productivity and disease suppression in different agro-ecosystems.
Highlights
The use of Organic Amendments (OAs) has been considered a recommended practice in conventional and organic agriculture
We found that OAs response to decomposition could be categorized into four main groups: the first includes only humus that was consistently suppressive, the second group is made of N rich OAs that were conducive in the short and medium term, but suppressive thereafter, the third group showed a trend of increasing suppression with decomposition time
This study systematically explored the interaction between OAs types and decomposition time, demonstrating that most of the organic materials were either suppressive or conducive to damping-off in relation to feedstock origin and incubation time
Summary
The use of Organic Amendments (OAs) has been considered a recommended practice in conventional and organic agriculture. Addition of OAs in agricultural soil, enhance soil fertility and structure [1,2] and, protect crops by controlling diseases caused by soilborne pathogens [3,4]. The introduction of synthetic fertilizers over the past centuries encouraged farmers to reduce the practice of OAs application [5] which in turns, limited the crucial role of OAs as soilborne pathogen controlling agents. In modern agriculture, the lack of suppressiveness from OAs bring to a dependencies by synthetic products for pests control. The public concerns about the effect of synthetic fertilizers, herbicides and fungicides on human health and environment resulted in the restriction of soil fumigants and fungicides that was the most effective way to control soilborne pathogens. Fungicide resistance in pathogens and the unreliability of chemical control have contributed to the development of a variety of alternative control measures [6]
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