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[en] Improving food security, environmental preservation and enhancing livelihood should be the main targets of the innovators of today's farming systems. Conservation agriculture (CA), based on minimum tillage, crop residue retention and crop rotations, has been proposed as an alternative system combining benefits for the farmer with advantages for the society. This paper reviews the potential impact of CA on C sequestration by synthesizing the knowledge of carbon and nitrogen cycling in agriculture, summarizing the influence of tillage, residue management and crop rotation on soil organic carbon stocks and compiling the existing case study information. To evaluate the C sequestration capacity of farming practices, their influence on emissions from farming activities should be considered together with their influence on soil C stocks. The largest contribution of CA to reducing emissions from farming activities is made by the reduction of tillage operations. The soil C case study results are not conclusive. In 7 of the 78 cases withheld, the soil C stock was lower in zero compared to conventional tillage, in 40 cases it was higher and in 31 of the cases there was no significant difference. The mechanisms that govern the balance between increased or no sequestration after conversion to zero tillage are not clear, although some factors that play a role can be distinguished e.g. root development and rhizodeposits, baseline soil C content, bulk density and porosity, climate, landscape position and erosion/deposition history. Altering crop rotation can influence soil C stocks by changing quantity and quality of organic matter input. More research is needed, especially in the tropical areas where good quantitative information is lacking. However, even if C sequestration is questionable in some areas and cropping systems, CA remains an important technology that improves soil processes, controls soil erosion and reduces tillage-related production costs. (author)
[en] In a previous laboratory experiment, extracts of neem (Azadirachta indica A. Juss.) and Gliricidia sepium Jacquin, locally known as mata-raton, used to control pests on crops, inhibited emissions of CO2 from a urea-amended soil, but not nitrification and N2O emissions. We investigated if these extracts when applied to beans (Phaseolus vulgaris L.) affected their development, soil characteristics and emissions of carbon dioxide (CO2) and nitrous oxide (N2O) in a greenhouse environment. Untreated beans and beans planted with lambda-cyhalothrin, a commercial insecticide, served as controls. After 117 days, shoots of plants cultivated in soil amended with urea or treated with lambda-cyhalothrin, or extracts of neem or G. sepium were significantly higher than when cultivated in the unamended soil, while the roots were significantly longer when plants were amended with urea or treated with leaf extracts of neem or G. sepium than when treated with lambda-cyhalothrin. The number of pods, fresh and dry pod weight and seed yield was significantly higher when bean plants were treated with leaf extracts of neem or G. sepium treatments than when left untreated and unfertilized. The number of seeds was similar for the different treatments. The number of nodules was lower in plants fertilized with urea, treated with leaf extracts of neem or G. sepium, or with lambda-cyhalothrin compared to the unfertilized plants. The concentrations of NH4+, NO2- and NO3- decreased significantly over time with the lowest concentrations generally found at harvest. Treatment had no significant effect on the concentrations of NH4+ and NO2-, but the concentration of NO3- was significantly lower in the unfertilized soil compared to the other treatments. It was found that applying extracts of neem or G. sepium leaves to beans favored their development when compared to untreated plants, but had no significant effect on nitrification in soil.
[en] Addition of different forms of nitrogen fertilizer to cultivated soil is known to affect carbon dioxide (CO2) and nitrous oxide (N2O) emissions. In this study, the effect of urea, wastewater sludge and vermicompost on emissions of CO2 and N2O in soil cultivated with bean was investigated. Beans were cultivated in the greenhouse in three consecutive experiments, fertilized with or without wastewater sludge at two application rates (33 and 55 Mg fresh wastewater sludge ha-1, i.e. 48 and 80 kg N ha-1 considering a N mineralization rate of 40%), vermicompost derived from the wastewater sludge (212 Mg ha-1, i.e. 80 kg N ha-1) or urea (170 kg ha-1, i.e. 80 kg N ha-1), while pH, electrolytic conductivity (EC), inorganic nitrogen and CO2 and N2O emissions were monitored. Vermicompost added to soil increased EC at onset of the experiment, but thereafter values were similar to the other treatments. Most of the NO3- was taken up by the plants, although some was leached from the upper to the lower soil layer. CO2 emission was 375 C kg ha-1 y-1 in the unamended soil, 340 kg C ha-1 y-1 in the urea-amended soil and 839 kg ha-1 y-1 in the vermicompost-amended soil. N2O emission was 2.92 kg N ha-1 y-1 in soil amended with 55 Mg wastewater sludge ha-1, but only 0.03 kg N ha-1 y-1 in the unamended soil. The emission of CO2 was affected by the phenological stage of the plant while organic fertilizer increased the CO2 and N2O emission, and the yield per plant. Environmental and economic implications must to be considered to decide how many, how often and what kind of organic fertilizer could be used to increase yields, while limiting soil deterioration and greenhouse gas emissions.
[en] Agricultural application of wastewater sludge has become the most widespread method of disposal, but the environmental effects on soil, air, and crops must be considered. The effect of wastewater sludge or urea on sunflower's (Helianthus annuus L.) growth and yield, the soil properties, and the resulting CO2 and N2O emissions are still unknown. The objectives of this study were to investigate: i) the effect on soil properties of organic or inorganic fertilizer added to agricultural soil cultivated with sunflower, ii) how urea or wastewater sludge increases CO2 and N2O emissions from agricultural soil over short time periods, and iii) the effect on plant characteristics and yield of urea or wastewater sludge added to agricultural soil cultivated with sunflower. The sunflower was fertilized with wastewater sludge or urea or grown in unamended soil under greenhouse conditions while plant and soil characteristics, yield, and greenhouse gas emissions were monitored. Sludge and urea modified some soil characteristics at the onset of the experiment and during the first two months but not thereafter. Some plant characteristics were improved by sludge. Urea and sludge treatments increased the yield at similar rates, while sludge-amended soil significantly increased N2O emissions but not CO2 emissions compared to the other amended or unamended soils. This implies that wastewater sludge increased the biomass and/or the yield; however, from a holistic point of view, using wastewater sludge as fertilizer should be viewed with concern.