IMPACT OF VERMICOMPOST AND NITROGEN-PHOSPHORUS- POTASSIUM APPLICATION ON BIOMASS PARTITIONING,NUTRIENT UPTAKE AND PRODUCTIVITY OF ARECANUT

A long-term field experiment (1998 to 2010) investigated the effects of vermicompost (VC) and chemical fertilizers (CF) application alone or in combination on biomass partitioning, nutrient uptake and productivity of arecanut. Trunk biomass (kg palm^?1) was significantly higher with integrated treatments (40.8–43.0) than control (23.9). Biomass partitioning to kernel varied between 4.6% in control to 7.7% in CF 100 and 200% nitrogen (N)- phosphorus (P)- potassium (K). The leaf P and K content varied significantly among treatments. The N immobilized in trunk (g palm^?1) was significantly higher in integrated treatments (119-127) than in control (93). Phosphorus and K uptake by trunk followed same trend. The leaf K uptake and total K removed were found significant. The nutrition treatments registered significantly higher kernel yield (2508–3176 kg ha^?1) than control (1721 kg ha^?1). The increased yield of arecanut from chemical fertilizers (73–85%) was more pronounced when compared to VC (48–59%) and integrated treatments (46–63%) over control.     

Mutualism between euryhaline tilapia Sarotherodon melanotheron heudelotii and Chlorella sp.—Implications for nano-algal production in warmwater phytoplankton-based recirculating systems

The West-African euryhaline tilapia, Sarotherodon melanotheron heudelotii shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults. When reared using an appropriate ration in intensive aquaculture systems, S. m. heudelotii also consume algal-based detritus, and contribute to sediment mineralization, clean up their environment, and ultimately stimulate and sustain algal growth. We analysed such practical advantages for phytoplankton-based recirculating systems, using S. m. heudelotii and Chlorella sp. as biological material originating from the prototype of such a system operated in Senegal. We performed a 24-h factorial design experiment in 36 tubs, cross-classifying three levels of S. m. heudelotii (fishless control, unfed fish, and fed fish) with four levels of Chlorella initial density.Chlorella overall mean density increased significantly from fishless, to unfed fish, and fed fish treatments, and with Chlorella initial density. S. m. heudelotii did not alter nitrogen nor phosphorus concentrations, only affected by algal initial densities. Most ammonia excreted by fish was probably uptaken by Chlorella. Bacteria-mediated diurnal nitrification was possibly an alternative ammonium loss mechanism at highest oxygen concentrations. Algae were not limited by nitrogen or phosphorus but most likely by low dissolved organic carbon availability. Chlorella differential responses with fed vs. unfed Sarotherodon suggest that CO₂ supplied by heterotrophic S. m. heudelotii respiration played a key role. Observed Chlorella growth rates were similar to the highest rates obtained in algal mass cultures, enriched with CO₂, nitrate and phosphate, under artificial lighting.Our results suggest the existence of a Sarotherodon-Chlorella mutualism in our systems, where S. m. heudelotii provide CO₂, the major limiting factor of Chlorella growth, whereas Chlorella oxygenate and detoxify the water media from ammonia, promoting S. m. heudelotii production. This mutualism could be used to optimize photosynthetic suspended-growth aquaculture systems, particularly in the Tropics where light is abundant and temperature is continuously high.     

Agroforestry systems and soil surface management of a tropical alfisol:

Field runoff plots, 70 x 10 m each, were established on a tropical Alifisol in southwestern Nigeria to monitor water runoff, soil erosion and nutrient loss in water runoff. The non-agroforestry control treatment (A) was established at two levels: plow-till and no-till systems of seedbed preparation. There were two agroforestry systems based on contour hedgerows of (B) Leucaena leucocephala and (C) Gliricidia sepium established at 4-m and 2-m spacings. Field plots were established in 1982 and hydrological measurements were made for uniform maize-cowpea rotation for 12 consecutive growing seasons from 1982 through 1987. Once established hedgerows of Leucaena at 2-m spacing were extremely effective in reducing water runoff and controlling erosion. Runoff, erosion and nutrient losses were generally more from maize grown in the first season than from cowpea grown in the second. Mean seasonal erosion from maize was 4.3, 0.10, 0.57, 0.10, 0.64 and 0.60 t/ha for plow-till, no-till, Leucaena-4m, Leucaena-2m, Gliricidia-2m treatments, respectively. Mean runoff in the first season from treatments listed in the order above was 17.0, 1.3, 4.9, 3.3, 4.3, and 2.4 percent of the rainfall received. There were high losses of Ca and K in water runoff from the plow-till treatment. In contrast to runoff and erosion, losses of bases in water runoff from agroforestry treatments were relatively high, high concentration of bases in runoff was probably due to nutrient recycling by the deep-rooted perennials.     

Water and nutrient use efficiency of a low-cost hydroponic greenhouse for a cucumber crop: An Australian case study

The Australian greenhouse industry is primarily dominated by low-cost hydroponic greenhouses for delivery of water and nutrients to plants to grow a variety of vegetable crops including cucumber and tomato. The nutrient rich drainage water from these greenhouses is generally released into the local environment causing pollution concerns. This study was initiated to investigate the opportunities in recycling drainage water to increase water and nutrient-use efficiency of hydroponic greenhouses and reduce the environmental impact of the drainage water discharge. Results indicated that a total of 4.15 ML/ha of irrigation water was applied during the 13 weeks crop growing period of which 2.56 ML/ha was drained off and 1.59 ML/ha was used to meet the crop evapotranspiration demand. The study showed that the recycling of the drainage water resulted in a 33% reduction in potable water used for irrigation in cucumber production. The drainage water contained 59% applied N, 25% applied P and 55% applied K and illustrated the potential for nutrient recovery and production cost savings through the reuse of drainage water. This case study demonstrates that some relatively simple changes in irrigation practices within greenhouse systems to recycle drainage water can considerably improve sustainability of low-cost hydroponic greenhouses and help minimise the environmental footprint of the greenhouse industry.     

建筑中水回用及其存在的问题

建筑中水回用技术是解决当前某些缺水城市水资源危机的重要途径。本文在简要介绍建筑中水水源的基础上,通过分析前人试验和已建中水回用系统,从处理工艺的技术可行性和经济性可行性等方面出发,对建筑可用中水处理工艺进行了介绍,同时还对建筑中水回用存在的问题和发展趋势进行了分析。