Gaseous nitrogen losses from a soilless culture system in the greenhouse

Gaseous nitrogen losses from a closed-loop rockwool system were investigated during the vegetative growth and the stem fruit stage of cucumbers. On average 12.4% of the N input were released in form of N₂O and N₂. This was equivalent to a mean emission rate of 0.62 kg nitrogen per hectare greenhouse area and day. The highest emission rates occurred during the stem fruit development as an increased root decay and an intensive substrate respiration came on. The proportion of N₂O in the gaseous nitrogen losses decreased with increasing N₂O+N₂ evolution. On average it amounted to 9.6%.A comparison of different cucumber crops during the season showed that the gaseous nitrogen losses were nearly twice as high in the summer as in the autumn. Thus it proceeded almost parallel to the plant growth which also doubled. Furthermore, an effect of the substrate temperature is conceivable, since it was 3–4°C higher in the radiation-rich summer-time.With increasing root density in the substrate gaseous nitrogen losses increased while the N₂O/N₂ ratio declined. Possible reasons for this were a greater rhizodeposition of easily decomposable organic substances, an accelerated oxygen consumption by root respiration and a high density of microorganisms in close vicinity to the roots. The growth of green algae on the substrate surface stimulated the production of N₂O.     

Influence of nutrient solution pH on N2O and N2 emissions from a soilless culture system

The influence of nutrient solution pH on the emission of N2O and N2 was investigated during cultivation of cucumbers in a closed-loop rockwool system. Between pH 4 and 7 these gaseous nitrogen losses increased from 1.6 to 21.1% of the N fertilizer input. This was equivalent to average flux rates of 0.06 and 0.85 kg nitrogen per hectare greenhouse area and day, respectively. The N2O/N2 ratio was inversely related to the total gaseous nitrogen losses. At neutral pH dinitrogen was the main emission product, whereas more acidic conditions favoured the emission of nitrous oxide. The pH effects were probably not indirectly affected by root respiration or exudation as much as by a direct inhibition of the activity of denitrifying microorganisms due to high H+ concentrations since similar results were obtained in unplanted nutrient solution systems with the addition of glucose as carbon source. Despite the low microbial denitrification activity under acidic conditions, nitrogen balance deficits of up to one-fifth of the N input still occurred. It is suggested these losses were predominantly caused by chemodenitrification.     

Using Health Surveillance Systems Data to Assess the Impact of AIDS and Antiretroviral Treatment on Adult Morbidity and Mortality in Botswana

Introduction

Botswana''s AIDS response included free antiretroviral treatment (ART) since 2002, achieving 80% coverage of persons with CD4<350 cells/µl by 2009–10. We explored impact on mortality and HIV prevalence, analyzing surveillance and civil registration data.

Methods

Hospital natural cause admissions and deaths from the Health Statistics Unit (HSU) over 1990–2009, all-cause deaths from Midnight Bed Census (MNC) over 1990–2011, institutional and non-institutional deaths recorded in the Registry of Birth and Deaths (RBD) over 2003–2010, and antenatal sentinel surveillance (ANC) over 1992–2011 were compared to numbers of persons receiving ART. Mortality was adjusted for differential coverage and completeness of institutional and non-institutional deaths, and compared to WHO and UNAIDS Spectrum projections.

Results

HSU deaths per 1000 admissions declined 49% in adults 15–64 years over 2003–2009. RBD mortality declined 44% (807 to 452/100,000 population in adults 15–64 years) over 2003–2010, similarly in males and females. Generally, death rates were higher in males; declines were greater and earlier in younger adults, and in females. In contrast, death rates in adults 65+, particularly females increased over 2003–2006. MNC all-age post-neonatal mortality declined 46% and 63% in primary and secondary level hospitals, over 2003–2011. We estimated RBD captured 80% of adult deaths over 2006–2011. Comparing empirical, completeness-adjusted deaths to Spectrum estimates, declines over 2003–2009 were similar overall (47% vs. 54%); however, Spectrum projected larger and earlier declines particularly in women. Following stabilization and modest decreases over 1998–2002, HIV prevalence in pregnant women 15–24 and 25–29-years declined by >50% and >30% through 2011, while continuing to increase in older women.

Conclusions

Adult mortality in Botswana fell markedly as ART coverage increased. HIV prevalence declines may reflect ART-associated reductions in sexual transmission. Triangulation of surveillance system data offers a reasonable approach to evaluate impact of HIV/AIDS interventions, complementing cohort approaches that monitor individual-level health outcomes.