The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na+ and Cl- in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na+ and Cl- in shoots probably caused harmful effects and reduced growth of plants.

Organic fertilizers have recently been gaining popularity; however, their governance is not completely assessed in developing countries. This study investigated the nutrient composition of so-called organic fertilizers in Vietnam's markets and issues related to their production, and evaluated their potential to contaminate the groundwater. We analyzed the physicochemical properties of 12 domestic and four imported products of the fertilizers, and conducted a cultivation experiment in sandy soil with the fertilizer applied at a rate of 200 mg N kg −1 soil using an automatic watering apparatus in a greenhouse. We further studied the production of an "organic fertilizer" from coffee by-products. The nutrient content greatly varied among domestic products, whereas they were quite similar among imported products. The product packaging of the collected samples lacked information regarding raw materials. Two thirds of the domestic products contained over 30% of the total N in the inorganic form, implying that the N content dramatically increased in the fertilizers rather than in their supposed raw materials. The stages involved in the production were composting, the addition of extra soil as a bulking agent, and the mixing-in of chemical substances to increase the nutrient content before packing. The remarkably high ratio of inorganic N to total N was attributed to excessive N leaching from soil by the application of domestic fertilizers. These results suggested the need for quality criteria guidelines for organic fertilizers in Vietnam that underline not only nutrient levels, but also the control of raw materials and production process of compost, because they are closely related to nutrient uptake and the leaching loss of nutrients.

The objective of this study was to examine the feasibility of sewage sludge composting using a simple aeration method. Two consecutive composting trials (run A and run B) using Japanese sludge and woodchips (1:1, v/v) were conducted in cubic boxes (0.45 × 0.45 × 0.45 m) made by plywood at Okayama University. Air was forced up through small holes perforated on two open-ended parallel PVC pipes (ø 16 mm, 0.25 m apart) laid at the base. The results show that compost temperatures were rapidly increased to the peak points of 47.4 °C (run A) and 74.8 °C (run B) within the first 2-3 days and varied depending on each composting run and vertical locations. The changes in physicochemical properties with particular attention to inorganic nitrogen (NH-N, NO-N) and free amino acid nitrogen (FAA-N) indicated that the biodegradation took place by different mineralization pathways during the composting process. The degradation of organic matter into amino acids followed by ammonification was predominant in run B, whereas the nitrification was greater in run A. A pot experiment using the two finished composts and their raw materials was carried out to study their effectiveness as fertilizer to Komatsuna (Brassica rapa var. perviridis). The total plant biomass produced by the composts was similar to chemical fertilizer. The lowering proportions of FAA-N/T-N, NH-N/NO-N, and C/N ratios in the composts compared to those in raw materials was found to correlate with the increase in plant biomass.

Plant residues supply carbon-rich source but also affect nitrogen (N) dynamic in the plant-soil system. Two consecutive incubations were conducted to examine soil net N mineralization from compost and urea as affected by additions of carbon sources with controlled C/N ratios. For incubation 1-set 1, powder of bamboo stem (BS) was incorporated into paddy soil with increasing rates from 0 to 2457.2 mg total C/kg soil that can cover a wide range of C used in the later incubations. For incubation 1-set 2, either sewage sludge compost or urea was added with BS to increase their C/N ratios up to 10 and 25. Amended materials were then incorporated into paddy soil at the same rate of 100 mg total N/kg soil. For incubation 2, we compared the effectiveness of three different carbon sources, i.e., BS, powder of residual wood for building (WB) and rice straw (RS) on potential N immobilization of compostamended sandy soil after regulating C/N values of amendments up to 25. The major results obtained were as follows: 1) The net N mineralization rates decreased with increasing amounts of added-C, indicating the immediate availability of the BS. 2) N immobilization of nitrate was greatest in treatment of BS and compost (C/N=25), whereas, N immobilization of ammonium was found in treatments of BS and urea (both C/N=10 and C/N=25). 3) N immobilization was significantly greater in the soil incorporated with BS and RS than that with WB. Our findings suggest that the mineralization-immobilization turnover (MIT) of N in soil can be controlled by adding readily available plant residues. 

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