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Poster Session 5
“The role of organic matter and biological activity”

Mineralization of organic amendments in a sandy soil of Central Vietnam

Backer, C.D.1; Q.H. Pham2; N.C. Chiang1 and J.E. Dufey1

Keywords: Soil organic matter management, manures, tropics, sandy soils


Farming systems in sandy areas of the tropics require special attention to the management of organic matter. According to a recent survey within the Vietnam-Belgium joint project, a great diversity of organic materials is used by farmers in the coastal sandy zone of Central Vietnam. Research is currently being conducted to evaluate the fertilization capacity of various organic amendments. The poster presents the first results on the mineral-N evolution through the incubation of an acid sandy soil from the Thua Thien Hue Province, amended with 4 types of organic matter: buffalo manure (BM), pig manure (PM), chicken manure (CM), and ash + urine (AU). Along with NH4+ and NO3- measurements, pH, electrical conductivity (EC), and redox potential (Eh) were monitored during incubation. Two laboratory experiments were undertaken according to the incubation method recommended by Keeney (1982) under anaerobic conditions at 37ºC; the first experiment was conducted with 30 g organic amendment per kg of soil for 0, 2, 5, 10, and 20 days as incubation times; the second was carried out with 20 and 40 g organic matter per kg of soil during one week.

Initially, significant amounts of NO3- are found with PM and CM, whereas AU released only NH4+. Limited amounts of inorganic N were released by BM. During the first week of incubation, there was a rapid, but temporary, drop of Eh, and increase of pH, EC and NH4+ concentration in the soil solution. NO3- disappeared quickly for PM and CM. Only slight variations of these parameters were observed after 10 days, which justified the short incubation period to screen organic matter amendments for their N fertilization capacity, notwithstanding their long term contribution to the soil organic pool. Total inorganic N release was in the order CM > AU > PM ≈ BM.

It is worth noting that organic amendments increased soil alkalinity, or soil acid neutralization capacity (release of bicarbonate anions), which can be roughly inferred by pH increase at similar Eh and CO2 pressure values. For a soil amended with 3% organic matter, the pH values after 20 days were approximately 8 for CM and AU, about 6.5 for PM and BM, compared to 5 for the control soil.

1 Universit?atholique de Louvain, Facult??Ing?ierie Biologique, Agronomique et Environnementale, Croix du Sud 2/10, 1348 Louvain-la-Neuve, Belgium.
National Institute for Soils and Fertilizers, Chem – Tu Liem, Hanoi, Vietnam.

Patterns of soil organic carbon and nitrogen in grazed and un-grazed
exclosures of semi-arid rangelands in South Africa

Moussa, A.S.1; L.V. Rensburg1; K. Kellner1 and A. Bationo2

Keywords: Overgrazing, soil organic matter, exclosures


Approximately 66% of the total rangeland surface has become degraded in South Africa. Overall synthesis derived from participatory research has shown that communal rangeland management characterized by overgrazing and overstocking is unsustainable and will lead to irreversible rangeland degradation. However, there is scant quantitative information on the influence of soil factors on rangeland degradation in some of these areas. In this study, we examined the effects of livestock grazing and exclusion on soil organic carbon and nitrogen (nitrate and ammonium) at three communal sites (Austrey 1, Eska/Neuhan and Tseoge). Soil samples were collected at 30 cm depth in April 2004 from open grazed plots and 5 year exclosures. Anova and Tukey HSD (p <0.05) were used to test significant differences. Only organic carbon was significantly different across sites (p = 0.049), averaging 0.18 mg kg-1. Overall no significant difference was recorded at the sites for organic carbon (p = 0.37), NO3- (p = 0.66), and NH4+ (p = 0.90) between grazed and un-grazed plots. Patterns of soil variables differed across sites. At Eska/Neuhan and Tseoge sites, organic carbon increased with grazing, while it decreased at Austrey 1. Nitrate increased at Austrey 1 and Tseoge whereas it decreased at Eska/Neuhan. Results from this study showed that grazing-induced rangeland degradation is site-specific and might be related to some other factors.

1 School of Environmental Sciences and Development, Northwest University (Potchefstroom Campus), Private Bag x6001 Potchefstroom 2520, South Africa
Tropical Soil Biology and Fertility, Institute of the International Center for Tropical Agriculture (TSBF-CIAT) P.O. Box 30677 Nairobi, Kenya

Selection of bacteria from soil samples for liquid biofertilizer production

Piamtongkam, R.1; T. Yongvanich2 and W. Chulalaksananukul3


Twelve isolates of bacteria which could produce cellulase, protease and lipase, were screened from already identified bacteria from several locations including; soil surrounding a food waste dumping area in Bangkok; soil around a hot spring area from Sankampang, Chiang Mai, Thailand; decomposed vegetables and compost from The Royal Project, Chitralada Palace. The selected bacteria were identified as 5 isolates of Bacillus cereus, 1 isolate of Bacillus subtilis, 4 isolates of Bacillus coagulans, 1 isolate of Serratia marcescens and 1 isolate of Pseudomonas aeruginosa. When the enzyme activities were detected, the bacterial isolates with the highest activities of each enzyme were selected for the experimental production of liquid biofertilizer from solid waste. The result from the antagonistic test revealed that these bacteria could be grown together without inhibiting each other and were suitable for biofertilizer production. The solid wastes were then sampled from home food waste and synthetic waste composed of the leftovers from vegetables, animals and used oil in the ratio of 1:1:1 by weight. The liquid biofertilizer consisted of 6 pots as follows: Pot 1 – home food waste; Pot 2 – home food waste with 12 isolates of bacteria; Pot 3 – synthetic waste; Pot 4 – synthetic waste with 12 isolates of bacteria; Pot 5 – autoclaved synthetic waste; and Pot 6 – autoclaved synthetic waste with 12 isolates of bacteria. After 30 days of composting, the properties of the product were determined and were as follows: temperature = 28ºC, pH = 7.5-8.5, moisture content = 80%; C/N ratio = 8.00-16.80 and nutritional values N, P, K; 1.40, 1.20, 1.23 gm% respectively. From these results the nutritional values obtained from the liquid biofertilizers were higher than that obtained from fish waste and some other types of biofertilizers. In addition, the rate of decomposition was more complete. Therefore, the bacteria from this study were appropriate for the decomposition of the waste and hence useful for the production of the liquid biofertilizers.

1 Program of Biotechnology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand
Department of Botany, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand

Management of subsoil hard pans in tropical sodic sandy soil

Kaleeswari, R.K.1; R. Kalpana1 and P. Devasenapathy1

Keywords: Sodic soils, hardpan formation, ploughing, gypsum, coir


The deflocculation of soil particles and organic matter in sodic sandy soils leads to the formation of subsoil hardpans. The presence of a hardpan at a depth of 30 cm from the soil surface limits the cultivation of deep rooted crops by hindering root penetration, movement of water and plant nutrients. A field experiment was conducted using annual moringa (Moringa oleifera Lam.) as test crop. Management strategies involving integrated effect of ameliorating measures viz., mechanical (tillage methods-chisel ploughing), chemical (application of gypsum as per the Gypsum Requirement of soil) and organic ameliorants (composted coir waste, raw coir waste and FYM) were assessed. The influence of subsoil hard pan in tropical sandy soils on root penetration, root volume, hydraulic conductivity, soil bulk density and soil moisture retention characteristics were studied. The results revealed that hydraulic conductivity, soil moisture content, root volume and root penetration ratio were increased due to the integrated use of chisel ploughing, composted coir waste and gypsum. Chisel ploughing and organic amendments incorporation reduced the soil bulk density.

1 Department of Agronomy, Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India

Nitrogen dynamics under different farmer practices in sandy salt-affected
paddy fields in Northeast of Thailand

Suvannang, N.1; C. Quantin2; O. Grunberger3; J.L. Maegh3 and S. Chutchitt1

Keywords: N dynamic, Organic Matter incorporation, salt-affected sandy soils, Rice fields, Northeast Thailand


Soil salinity hazard along with nitrogen mineralization has been identified as the main limiting factors for rice production in Northeast paddy fields. Management activities in rice systems, such as fertilization and Organic Matter (OM) incorporation, affect losses of N through denitrification activity. The aim of the study was to quantify the effects of different farmer practices and level of salinity on the Nitrogen dynamic in soil solution. Two neighbouring fields with different farmer practices were selected. One field was managed with the incorporation of OM and supplied with fertilizers while the other had no amendment at all. Soil solution sampling was performed each week in 2004, at three depths (10, 25 and 45 cm) over a 3 month period under flooded conditions. In each field, sampling was performed in two profiles with distinct salinity levels. Samples were analyzed for NH4-N and NO3-N. Results indicated that accumulation of mineral N during cropping period demonstrated the capacity to supply sufficient N to produce reasonable rice yields. Evidences of the influence of OM incorporation, fertilizer application and anaerobic soil conditions were found on the dynamics and distribution patterns of NH4-N in the soil solution. OM management resulted in sufficient NH4-N supply for rice in the root zone and enhanced nitrification-denitrification processes. Salinity influenced the rate of mineralization, nitrification-denitrification processes, leading to potential NO3-N contamination of groundwater, especially under extreme salinity conditions. With no OM incorporation, nitrification-denitrification was depleted due to lack of carbon source for microbial activity. It should be noted that further research is needed to confirm under controlled conditions, the influence of high salt contents on nitrogen dynamics.

1 Land Development Department, Office of Science for Land Development, Phaholyothin Road, Chatuchak, Bangkok 10900, Thailand
UMR 8148 IDES, Paris-Sud XI University, F-91405 Orsay Cedex, France
IRD – Land Development Department, office of Science for Land Development, Phaholyothin Road, Chatuchak, Bangkok 10900, Thailand

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