Nitrogen dynamics in maize-based agroforestry systems as affected by landscape position in southern Malawi

In Malawi, agroforestry is very promising for N replenishment; however, there are still large variations in the performance of these agroforestry technologies on farmers’ fields. A study was conducted on-farm to determine the influence of three landscape positions on N dynamics in maize (Zea mays L.)-based agroforestry systems. The agroforestry systems were relay fallow using Sesbania sesban (L.) Merr or Tephrosia vogelii (Hook F.), simultaneous fallow using Gliricidia sepium(Jacq.) Walp., and maize without trees as a control. Sesbania was superior to other systems in the bottom slope, producing the highest tree biomass (1,861 kg ha⁻¹), whereas, gliricidia gave the highest tree biomass production in the mid-slope (2,147 kg ha⁻¹) and upper slope (1,690 kg ha⁻¹). Preseason inorganic N, maize flag leaf N concentration, maize total N uptake and maize yields followed a similar trend to tree biomass production with tree-based cropping systems exhibiting higher productivity (P < 0.05) than the cropping systems without trees. Nitrogen leaching from gliricidia agroforestry systems was lower than in the other agroforestry systems across all landscape positions as evidenced by 17% lower amounts (P < 0.05) of inorganic N adsorbed to ionic exchange resin membranes at 60 cm soil depth most likely due to the permanent root system of gliricidia. The difference between δ¹⁵N values of the trees and the soil did not change between landscape positions suggesting that if the leguminous trees fixed atmospheric N₂, the proportion of total N uptake was identical at all locations. We concluded that landscape positions have a significant effect on tree performance with sesbania remarkably adapted to the bottom slope, gliricidia to the mid-slopes and tephrosia fairing similar in both the bottom slope and mid-slopes.     

Timing of lymphocyte activation in neonates infected with human immunodeficiency virus

PURPOSE: To report the results of vitreoretinal surgery for the management of complications associated with congenital retinoschisis in children. METHODS: We conducted a review of consecutive children with complications of congenital retinoschisis treated with advanced vitreoretinal techniques. Nine eyes of seven patients with congenital retinoschisis had vitreoretinal surgery for one of the following complications of congenital retinoschisis: hemorrhage within a large schisis cavity with a dense vitreous hemorrhage; rapid progression of schisis threatening the macula; obscuration of the macula by the overhanging inner wall of a schisis cavity; a combined schisistraction retinal detachment; or a combined schisis-rhegmatogenous retinal detachment. Vitreoretinal surgery consisted of vitrectomy, inner schisis wall retinectomy, fluid-gas exchange, endolaser treatment, and perfluoropropane gas injection. After vitreoretinal surgery, patients were followed up for a mean of 26 months (range, 9 to 67 months). Retinal reattachment, visual acuity, and visual fields were used as outcome measures. RESULTS: Eight of nine eyes had successful retinal reattachment. Six eyes postoperatively had improved visual acuity or visual field, or both. One eye had stabilization of visual acuity, and two eyes had a decrease in visual acuity. CONCLUSION: In children with complications of congenital retinoschisis, vitreoretinal surgery with excision of the inner wall of the peripheral schisis cavity may be effective in achieving retinal reattachment, thereby improving visual acuity or visual field size.     

Maize yield response,nitrogen use efficiency and financial returns to fertilizer on smallholder farms in southern Africa

Maize is considered as “life” in southern Africa because it is the staple food crop and the main component of food aid interventions. However, its productivity is very low, partly because of the limited use of external inputs. Although maize response to fertilizer has been the focus for many years of studies on research stations, information is scanty on the level of crop response and profitability on smallholder farms in most parts of southern Africa. Therefore, the objective of the present analysis was to determine yield responses, nitrogen use efficiency and returns to investment in fertilizer in the unimodal rainfall region of southern Africa. This analysis compared yield responses to various rates of nitrogen (N) fertilizer with maize grown without external inputs (absolute control) on a total of 940 demonstration sites in 47 districts across Malawi, Mozambique, Zambia and the southern highlands of Tanzania. Across the sites, average yields were 1.6 t ha^?1 in the control, 2.8 t ha^?1 with ≤50% of the recommended N rate and 4 t ha^?1 where 100% or more of the recommended N rate was applied. Except in Zambia, agronomic efficiency and partial factor productivity of N were higher with 50% of the recommended N rate compared to 100% of the recommended N rate. Net present values (NPV) were also positive in over 50% of the cases, indicating that investments in N fertilizer will generate profits over time. In contrast, for maize grown without N fertilizer, NPVs were negative in over 68% of the cases across the four countries. The value-cost ratio was >2 with the various N rates at the aggregate level, but it was <2 on sites in Mozambique and Zambia. We conclude that growing maize without N inputs results in loss of land productivity and profitability while application of 50% or more of the recommended N fertilizer ensures substantial increases in yields and profitability.