Legacy effects override soil properties for CO 2 and N 2 O but not CH 4 emissions following digestate application to soil

The application of organic materials to soil can recycle nutrients and increase organic matter in agricultural lands. Digestate can be used as a nutrient source for crop production but it has also been shown to stimulate greenhouse gas (GHG) emissions from amended soils. While edaphic factors, such as soil texture and pH, have been shown to be strong determinants of soil GHG fluxes, the impact of the legacy of previous management practices is less well understood. Here we aim to investigate the impact of such legacy effects and to contrast them against soil properties to identify the key determinants of soil GHG fluxes following digestate application. Soil from an already established field experiment was used to set up a pot experiment, to evaluate N2O, CH4 and CO2 fluxes from cattle‐slurry‐digestate amended soils. The soil had been treated with farmyard manure, green manure or synthetic N‐fertilizer, 18 months before the pot experiment was set up. Following homogenization and a preincubation stage, digestate was added at a concentration of 250 kg total N/ha eq. Soil GHG fluxes were then sampled over a 64 day period. The digestate stimulated emissions of the three GHGs compared to controls. The legacy of previous soil management was found to be a key determinant of CO2 and N2O flux while edaphic variables did not have a significant effect across the range of variables included in this experiment. Conversely, edaphic variables, in particular texture, were the main determinant of CH4 flux from soil following digestate application. Results demonstrate that edaphic factors and current soil management regime alone are not effective predictors of soil GHG flux response following digestate application. Knowledge of the site management in terms of organic amendments is required to make robust predictions of the likely soil GHG flux response following digestate application to soil

Azanza garckeana: A Valuable Edible Indigenous Fruit Tree of Botswana

Abstract: Azanza garkeana (morojwa) is a valuable edible indigenous fruit tree species confined to east and southern Africa. Because of its multiple use the species is selected and retained by farmers in Botswana when they clear the woodland for crops and building house. It is one of the indigenous fruit tree species that is semi-domesticated by local people in Botswana. The species is an important indigenous source of food in Botswana. Besides proving people with fruits, the tree also provides goods (timber, firewood, fodder etc.) and services (soil conservation, shade etc.). The species is an important source of essential minerals particularly P, Ca, Mg and Na. This paper reviews Azanza garckeana as an important multipurpose indigenous fruit tree with high potential social and economic value in Botswana. Key words: Azanza garkeana, edible indigenous fruit tree, Botswan