Effects of activated charcoal and quebracho tannins added to feed or as soil conditioner on manure quality in organic agriculture

• Published in: Organic agriculture 2015-12, Vol.5 (4), p.245-261
• Main Authors: Ingold, Mariko, Al-Kindi, Amal, Jordan, Greta, Dietz, Herbert, Schlecht, Eva, Buerkert, Andreas
• Format: Article
• Language: English
• Subjects: activated carbon; agricultural soils; Agriculture; arid lands; Biomedical and Life Sciences; carbon nitrogen ratio; crop yield; crops; Environment; feces; field experimentation; goat manure; goats; growth retardation; irrigated farming; Life Sciences; mineral fertilizers; nitrogen; nutrients; organic production; Plant Sciences; radishes; Raphanus sativus; sodium; soil conditioners; soil fertility; soil organic matter; soil quality; solar drying; Sustainable Development; sweetcorn; tannins; tropical agriculture; Zea mays
• ISSN: 1879-4238; 1879-4246
• DOI: 10.1007/s13165-015-0104-8

Animal manure is one of the major nutrient and carbon (C) sources in many low to medium input systems of irrigated agriculture in subtropical drylands, particularly if managed under the constraints of organic regulations. Under year-round hot and irigated conditions, high losses of C, nitrogen (N) and other nutrients may lead to soil quality deterioration and reduced crop yields. In an effort to develop approaches slowing down decomposition of soil applied manure, activated charcoal (AC) and quebracho tannin extract (QT) were either fed to goats or directly mixed with manure prior to application in a 2-year field experiment conducted with sweet corn (Zea mays L.) and radish (Raphanus sativus L.) in the Batinah Plain of Oman. Sun-dried faeces of goats fed AC had a 15 % higher C concentration and a 25 % higher C/N ratio than pure goat manure, whereas QT feeding only increased sodium (Na) concentration. While sweet corn performed best under equivalent mineral fertilization, the addition of AC and QT to goat feed or to goat manure reduced growth and development of sweet corn by 20 and 30 %, respectively, compared to pure goat manure, regardless of the application method. Radish yielded highest when fertilized with either pure goat manure or AC-amended goat manure, whereas mineral fertilizer and QT-amended manure applications inhibited its growth. Activated charcoal may be a promising additive to increase soil organic matter and increase soil fertility, if it does not hamper nutrient supply to crops. Quebracho tannins, however, impaired crop production, and further research is needed to evaluate whether tannins from other sources added to agricultural soils have similar detrimental effects on crops.