Potentially mineralizable nitrogen from organic materials applied to a sandy soil: fitting the one-pool exponential model

Abstract. Over the last three decades there has been a great increase in the production of waste from urban, industrial and agricultural activity that could be recycled as a source of plant nutrients, and used to enhance soil quality. The use of these materials could partially offset the need for mineral fertilizers, giving both economic and environmental benefits. An incubation experiment was carried out using different organic waste materials applied to a Cambic Arenosol. Air-dried soil was mixed with increasing amounts of composted solid municipal waste, secondary pulp-mill sludge, hornmeal, poultry manure, solid phase from pig slurry, and composted pig manure, resulting in applications equivalent to 0, 40, 80, 120, 160 and 200 kg ha⁻¹ of Kjeldahl nitrogen. The samples were incubated for 244 days under a controlled environment of 24 °C and 60% water holding capacity of the soil. The increasing amounts of waste applied always led to a greater amount of potentially available nitrogen present in the soil/waste mixture. Based on the proportion of their active N fraction, wastes were ranked: poultry manure>hornmeal>solid phase from pig slurry>composted pig manure>secondary pulp-mill sludge>composted municipal solid waste. The results were well described by a one-pool exponential mineralization model, and mineral N formation was proportional to the quantity of waste applied. Of the wastes tested, those from animal sources showed greater nitrogen mineralisation. Nitrification was rapid, and concentrations of ammonium nitrogen remained relatively small.     

Voracity of <Emphasis Type="Italic">Coccinella undecimpunctata</Emphasis>: effects of insecticides when foraging in a prey/plant system

Coccinella undecimpunctata L. is a euryphagous predator established in Azores that offers interesting potential as a control agent in the context of integrated pest management (IPM). However, to further develop IPM against aphids, it is important to evaluate the effects that insecticides might have on voracity. Thus, we proposed to evaluate the effects of pirimicarb and pymetrozine on the voracity of 4th instar larvae and adults of C. undecimpunctata, under distinct scenarios of exposure to chemicals within a prey/plant system. Voracity of C. undecimpunctata was not significantly affected by pirimicarb or pymetrozine when treatments were directly sprayed on the predator; however, when insecticides were sprayed on the prey/plant system, the predator’s voracity was significantly increased. Results suggest that C. undecimpunctata does not detect the insecticide on the aphids and indicate that the increase in voracity may be due to a decrease in the mobility of insecticide-treated aphids, since their capture should be easier than highly mobile non-treated prey. The consequences of such increase in the voracity for IPM programs are discussed.     

Nitrogen and carbon availability of liquid and solid fractions of pig slurry obtained using different separation technologies

Solid–liquid separation is now a common slurry management on European farms and many separation techniques are now available. The choice of technique used is based mostly on financial reasons even if the dry matter separation efficiency is also considered. Nevertheless, previous studies showed that the separation technique used influenced the composition of the resulting liquid (LF) and solid (SF) fractions. Hence, our hypothesis is that separation technique influences the C and N dynamics in soils amended with the resulting SF and LF. A laboratory incubation was performed with a sandy soil to assess the influence of five different separation techniques on the N and C dynamics in soil amended with the resulting LF and SF, namely the potential of each fraction for N and organic matter supply to plant and soil systems. Our results showed that the separation technique affects significantly the soil C pools in soils amended with the resulting LF and SF. Nevertheless, the differences between SFs were very low, whereas higher C losses were observed from LFs obtained with active separation techniques such as sieving relative to passive techniques such as sediment settling. The N dynamics in soils amended with the different SF obtained were similar but the extent of NH₄ ⁺ immobilization differs with the LF considered. Furthermore, higher and faster nitrification was observed with LFs obtained by sediment settling and centrifugation relative to sieving. A higher N mineralization relative to untreated slurry was observed in most fractions and the N mineralization rates were significantly influenced by the separation technique.