The effects of straw burning and drying-rewetting cycles on nutrient availability were studied in an attempt to assess the practical importance of the yearly precropping practice by farmers of burning off excess crop residues and of the seasonal climate of North-East Nigeria. Changes in soil properties resulting from heating three soils up to 700°C and from field burning of straw on three soils were determined. Heating to 250° did not affect soil texture but increased exchangeable NH4+-N, available P, Fe, Mn and phosphate adsorption. A peak of NH4+-N representing decomposed organic N, retained by cation exchange sites was observed after heating at 250°. Soil physical and chemical properties were changed by heating to ≥500^o, resulting in fusion of clay particles into sand-sized particles, decomposition of soil organic matter and alteration of soil minerals with a corresponding increase in non-exchangeable cation status of the soils. The changes observed after field burning of straw were mainly due to deposition of ash; these include a dramatic increase in phosphate adsorption and addition of considerable amounts of inorganic P and exchangeable cations. The availability to maize of the inorganic P returned in ash after field burning or released as a result of laboratory heating of soils was assessed over a 7 day period. The increased P status of the soils after straw burning or heating was not significantly reflected in plant uptake of P but K adsorption was enhanced from the ash. Fertilization of heated and field burnt + overlying ash soil samples resulted in adsorption of P with a corresponding reduction of P concentration in the soil solution and P uptake. The N mineralized after rewetting air-dried clay soils or those containing very low organic matter was insignificant. Investigations also showed that, when dried soils were rewetted, the flush of mineral N was derived mainly from soil organic matter and not from killed microbial cells.

No description available.

No description available.

The coralline soils of atolls suffer from multiple nutrient deficiencies that severely limit crop growth. This study was conducted to assess the nutrient status of the soils of the inhabited atolls within the Marshall Islands (MI), and to determine what local materials could be used to correct deficiencies limiting crop growth. Surface and subsoils from 25 atolls were collected and analyzed for their chemical properties, and soil test results were evaluated with a missing element pot study. Soil tests revealed that the MI soils were severely deficient in K (0.12 cmol c kg -1 ) and marginally deficient in Cu (0.13 ug g -1 ). The missing element study showed that the soil was deficient in K, S, N, P, and Cu. An incubation experiment and a series of greenhouse experiments were conducted to evaluate the ability of locally available organic materials to mineralize N and supply adequate nutrients to crops. Vigna marina and fish meal showed the highest N mineralization capacity, and the Gompertz equation provided the best fit. Chinese cabbage plants grew as well in soils amended with chicken manure, Vigna marina , and copra cake as they did in soil treated with chemical fertilizers. Plants grown in soil amended with fish meal did not grow as well due to inadequate K supply. Nitrogen recovery was highest in V. marina treatment at 92% followed by the chemical control (83%), chicken manure (34%), fish-meal (18%), and copra cake (9%). Added coconut leaves immobilized N and resulted in very poor cabbage growth. Comparisons between relative growth rate (RGR) and nutrient relative accumulation rate (RAR) showed that nutrients supplied from the V. marina amendment to the cabbage plant matched plant demand. In a rate experiment in the greenhouse, adding 10.1 g kg -1 of V. marina leaves (dry weight) supplied 350 mg N kg -1 to 5 week-old corn plants representing 38% of the total amount of N added in the amendment. Splitting the application quantity improved corn growth at the highest addition rate. Copra cake showed less promise as a suitable organic amendment. Supplementing copra with chemical N and P, and V. marina leaves with and without Cu and B did not improve crop growth compared with copra alone. The soil exhibited low P adsorption capacity, and corn and lettuce growth responded to high Olsen P soil levels. The results of the greenhouse experiments showed that V. marina is a potential organic fertilizer material to correct soil nutrient deficiencies for good crop growth in the Marshall Islands.

Por apresentar elevada capacidade de produção e por ser uma das poucas cultivares adaptadas à produção de "chips", a cultivar de batata 'Atlantic' responde por cerca de 80% do mercado brasileiro formal de batata consumida desta forma. Com os objetivos de determinar as curvas de crescimento de massa de material seco, o acúmulo máximo e a exportação de nutrientes, em lavouras comerciais, em duas safras, pela cv. 'Atlantic', realizou-se este trabalho nos períodos de setembro a dezembro de 2001(safra das águas) e de fevereiro a março de 2002 (safra da seca) em Itapetininga-SP, localizada na latitude 23 o 35'08" S, longitude 48 o 02'50" W e com 636 m de altitude. Para isso, foram delimitadas quatro parcelas de 100 m X 17 m em lavouras comerciais, das quais foram realizadas coletas semanais das plantas a partir de 20 dias após o plantio. As plantas coletadas foram separadas em raízes, caules, folhas e tubérculos e secas e pesadas para a obtenção da massa de material seco nos diferentes estádios de desenvolvimento, sendo posteriormente moídas, e submetidas à análise para a obtenção da extração de nutrientes ao longo do ciclo. A análise estatística dos parâmetros avaliados foi feita considerando-se as épocas de plantio e quatro repetições. Os resultados permitiram as seguintes conclusões: a safra das águas produziu mais massa de material seco que a safra da seca. O acúmulo de massa da planta foi influenciado pelos estádios da cultura e pela safra: vegetativo (2,2 e 5,2%) < tuberização (13 e 20%) < enchimento de tubérculos (90 e 95%) < maturação (100 e 100%) para a safra das águas e da seca, respectivamente. A seqüência de acúmulo máximo na safra das águas foi: nitrogênio > potássio > cálcio > fósforo > magnésio > enxofre > ferro > manganês > zinco > boro > cobre. Na safra da seca, o potássio trocou de posição com o nitrogênio e o fósforo com o cálcio. O acúmulo máximo dos nutrientes depende da safra e do nutriente: nitrogênio (140 e 119); fósforo (17,6 e15,2); potássio (134 e 139); cálcio (21,7 e 14,6); magnésio (14,3 e 6,9); enxofre (10,8 e 14,6) em kg ha -1 ; boro (107 e 84,3); cobre (43,5 e 38,9); ferro (1.229 e 790); manganês (250 e 130); zinco (156,6 e 124,6) em g ha -1, para as safras das águas e da seca, respectivamente. A seqüência de exportação de nutrientes pelos tubérculos na safra das águas foi: nitrogênio > potássio > fósforo > enxofre > magnésio > cálcio > ferro > zinco > boro > manganês > cobre. Na safra da seca, potássio trocou de posição nitrogênio e cobre com manganês. / By presenting a high yield potencial and being one of the few cultivars adapted for chipping, Atlantic potatoes are responsible for approximately 80% of the brazilian formal potato chips market. With the objective of determining the growth curves, maximum nutrient accumulation and nutrient exportation, this study was carried out in Itapetininga, São Paulo State, at 23o 35'08" S of latitude, 48o 02'50" W of longitude and 636 meters above sea level, in two commercial areas of Atlantic potatoes from September to December 2001 (wet season), and from February to March 2002 (dry season). Four plots with 100 m X 17 m were set in each experiment and plants were collected weekly, after 20 days from planting. The collected plants were separated in roots, stems, leaves and tubers, dried and weighted, to obtain the dry-matter at different stages of growth. Samples were ground and analized to obtain nutrients concentration and to calculate nutrients accumulations. Statistical analysis considered the season and four replications. Results showed that wet season potatoes had higher dry-matter production than those of dry season. Nutrient accumulation was influenced by growth stage and season: vegetative (2.2 and 5.2%) < tuberization (13 and 20%) < tuber bulking (90 and 95%) < maturation (100 and 100%) for wet and dry season, respectively. The maximum nutrient accumulation in the wet season was: nitrogen > potassium > calcium > phosphorus > magnesium > sulphur > iron > manganese > zinc > boron > copper. During dry season, potassium changed position with nitrogen, and phosphorus with calcium. Maximum accumulation of nutrients (kg ha-1 for macronutrients and g ha-1 for micronutrients) depended on the season and on the nutrient: nitrogen (140 and 119); phosphorus (17.6 and 15.2); potassium (134 and 139); calcium (21.7 and 14.6); magnesium (14.3 and 6.9); sulphur (10.8 and 14.6); boron (107 and 84.3); copper (43.5 and 38.9); iron (1229 and 790); manganese (250 and 130); zinc (156.6 and 124.6), for wet and dry season, respectively. The nutrient exportation by the tubers in the wet season was: nitrogen > potassium > phosphorus > sulphur > magnesium > calcium > iron > zinc > boron > manganese > copper. In the dry season, potassium changed position with nitrogen, and copper with manganese.

Por apresentar elevada capacidade de produção e por ser uma das poucas cultivares adaptadas à produção de "chips", a cultivar de batata 'Atlantic' responde por cerca de 80% do mercado brasileiro formal de batata consumida desta forma. Com os objetivos de determinar as curvas de crescimento de massa de material seco, o acúmulo máximo e a exportação de nutrientes, em lavouras comerciais, em duas safras, pela cv. 'Atlantic', realizou-se este trabalho nos períodos de setembro a dezembro de 2001(safra das águas) e de fevereiro a março de 2002 (safra da seca) em Itapetininga-SP, localizada na latitude 23 o 35'08" S, longitude 48 o 02'50" W e com 636 m de altitude. Para isso, foram delimitadas quatro parcelas de 100 m X 17 m em lavouras comerciais, das quais foram realizadas coletas semanais das plantas a partir de 20 dias após o plantio. As plantas coletadas foram separadas em raízes, caules, folhas e tubérculos e secas e pesadas para a obtenção da massa de material seco nos diferentes estádios de desenvolvimento, sendo posteriormente moídas, e submetidas à análise para a obtenção da extração de nutrientes ao longo do ciclo. A análise estatística dos parâmetros avaliados foi feita considerando-se as épocas de plantio e quatro repetições. Os resultados permitiram as seguintes conclusões: a safra das águas produziu mais massa de material seco que a safra da seca. O acúmulo de massa da planta foi influenciado pelos estádios da cultura e pela safra: vegetativo (2,2 e 5,2%) < tuberização (13 e 20%) < enchimento de tubérculos (90 e 95%) < maturação (100 e 100%) para a safra das águas e da seca, respectivamente. A seqüência de acúmulo máximo na safra das águas foi: nitrogênio > potássio > cálcio > fósforo > magnésio > enxofre > ferro > manganês > zinco > boro > cobre. Na safra da seca, o potássio trocou de posição com o nitrogênio e o fósforo com o cálcio. O acúmulo máximo dos nutrientes depende da safra e do nutriente: nitrogênio (140 e 119); fósforo (17,6 e15,2); potássio (134 e 139); cálcio (21,7 e 14,6); magnésio (14,3 e 6,9); enxofre (10,8 e 14,6) em kg ha -1 ; boro (107 e 84,3); cobre (43,5 e 38,9); ferro (1.229 e 790); manganês (250 e 130); zinco (156,6 e 124,6) em g ha -1, para as safras das águas e da seca, respectivamente. A seqüência de exportação de nutrientes pelos tubérculos na safra das águas foi: nitrogênio > potássio > fósforo > enxofre > magnésio > cálcio > ferro > zinco > boro > manganês > cobre. Na safra da seca, potássio trocou de posição nitrogênio e cobre com manganês. / By presenting a high yield potencial and being one of the few cultivars adapted for chipping, Atlantic potatoes are responsible for approximately 80% of the brazilian formal potato chips market. With the objective of determining the growth curves, maximum nutrient accumulation and nutrient exportation, this study was carried out in Itapetininga, São Paulo State, at 23o 35'08" S of latitude, 48o 02'50" W of longitude and 636 meters above sea level, in two commercial areas of Atlantic potatoes from September to December 2001 (wet season), and from February to March 2002 (dry season). Four plots with 100 m X 17 m were set in each experiment and plants were collected weekly, after 20 days from planting. The collected plants were separated in roots, stems, leaves and tubers, dried and weighted, to obtain the dry-matter at different stages of growth. Samples were ground and analized to obtain nutrients concentration and to calculate nutrients accumulations. Statistical analysis considered the season and four replications. Results showed that wet season potatoes had higher dry-matter production than those of dry season. Nutrient accumulation was influenced by growth stage and season: vegetative (2.2 and 5.2%) < tuberization (13 and 20%) < tuber bulking (90 and 95%) < maturation (100 and 100%) for wet and dry season, respectively. The maximum nutrient accumulation in the wet season was: nitrogen > potassium > calcium > phosphorus > magnesium > sulphur > iron > manganese > zinc > boron > copper. During dry season, potassium changed position with nitrogen, and phosphorus with calcium. Maximum accumulation of nutrients (kg ha-1 for macronutrients and g ha-1 for micronutrients) depended on the season and on the nutrient: nitrogen (140 and 119); phosphorus (17.6 and 15.2); potassium (134 and 139); calcium (21.7 and 14.6); magnesium (14.3 and 6.9); sulphur (10.8 and 14.6); boron (107 and 84.3); copper (43.5 and 38.9); iron (1229 and 790); manganese (250 and 130); zinc (156.6 and 124.6), for wet and dry season, respectively. The nutrient exportation by the tubers in the wet season was: nitrogen > potassium > phosphorus > sulphur > magnesium > calcium > iron > zinc > boron > manganese > copper. In the dry season, potassium changed position with nitrogen, and copper with manganese.

Thesis (Msc. (Agriculture)) --University of Limpopo, 2011 / The impact of agricultural chemicals on the environment has come under close scrutiny in the country of South Africa, for that reason, we are investigating alternative and appropriate methods for nutrients management. The objective of the study was to assess infield spatial variability of soil nutrients in a uniformly managed corn field, and (ii) to recommend method that can potentially help corn (Zea mays L.) producers in Limpopo Province to enhance grain yield with optimal utilization of resources. The study was conducted at Syferkuil agricultural experimental farm (23o50’ S; 29 o40’ E) of the University of Limpopo, in the northern semi-arid region of South Africa. Prior to planting of corn on this uniformly managed 7 ha portion of a 1 705 ha farm, the field was mapped with Ag132 Trimble differentially corrected global positioning system (DGPS) equipped with Field Rover II® GIS mapping software. Land suitability assessment for corn was conducted before planting and the field was classified for suitability as S1 based on FAO guidelines for irrigated agriculture and South African Binomial System of Soil classification. Soils and corn leaf sample parameters, including N were collected and measured from geo-referenced locations on a 40 x 40 m grid. Nutrient distribution spatial maps were produced with Surfer software 8.0. There was a significant variability (P≤0.05) of soil nutrients and pH across the corn field. Corn grain yield ranged from 2.7 to 6.3 Mg ha-1. For a land suitability class of S1 under linear irrigation in a semi-arid environment, these grain yields were considered lower. This lower grain yields can be linked to variability of soil nutrients, and pH because the field was classified suitable according to FAO guidelines. This field, with its significant variability of nutrients and pH that resulted in lower grain yields, is potentially a good field for precision agriculture IX methods of nutrient management such site-specific management zones for environmental quality and economic efficiency. Keywords: Maize, Small-scale farming, Soil nutrient management, and Spatial variability

Market gardening is commonly characterised by intensive cultivation, high inputs of both organic and inorganic fertilisers, chemical over/misuse, frequent irrigation, and a low degree of soil cover. While market gardening is readily perceived to be detrimental to waterways, there is remarkably little data to quantify the impacts. Soil and nutrient loss in stormwater runoff varies with soil type, climate and production systems. Therefore local data are needed to determine the impact of market gardening on the Hawkesbury-Nepean. This should lead to a better understanding of how land management influences runoff quantity and quality so that practices can be improved. Objectives of this research were to : quantify sediment, N and P loss and assess the implications for waterways; relate sediment, N and P losses to specific land management practices and assess their impacts on profitability; and, reflect on this research in terms of extension and adoption of better land management. An 8.8 ha property with 6.6 ha of market garden was used as a case study in the Hawkesbury-Nepean Catchment. Soil samples were collected at the beginning and end of the study. Sediment core samples were collected from the drainage channel. A rainfall simulator was used to compare runoff volume from green manure and bare fallow beds. The research produced several recommendations for the extension and adoption of improved land management. In order to reduce sediment, N and P losses in stormwater, the primary focus should be on improving soil and nutrient management, in particular matching fertiliser inputs more closely to nutrient requirements. The secondary focus should be on utilising structural measures, in particular farm dams, to prevent pollutants from entering waterways. The outcome should be decreased costs to the farmer and decreased impacts on waterways. The use of N-fixing green manure to decrease the use of poultry manure should be explored. / Master of Science (Hons)

Drought and poor soil fertility are often cited as major constraints to rainfed lowland rice production in Laos, particularly in the central and southern parts of the country, where uncertainty in the growing season is common, due mainly to a combination of unreliable rainfall and coarse textured soils with a low water holding capacity and high rates of deep percolation. The soil conditions, together with fluctuations in rainfall distribution, are regarded as the most serious constraints to achieving high and stable grain yields in the rainfed lowland rice ecosystem in this region. Improvements in rainfed lowland rice productivity depend, in part, on improved predictions of water availability, as well as better understanding of soil nutrient and water stress limitations to grain yield. The use of a soil water balance model, in conjunction with the quantification of soil nutrient availability, can help in estimating free water levels in the rice fields, thereby helping determine the duration of the growing period, as well as, helping with predictions of potential yield reduction due to water stress and soil nutrient limitations. Linking the simulated results with Geographic Information System (GIS) can help quantify the spatial pattern of these attributes at a provincial or regional scale. This study was aimed at quantifying the spatial distribution of water availability, including the frequency and severity of water stress development during the growing period, and to estimate the effects of soil fertility and water stress on rice productivity in Savannakhet province in southern Lao PDR. The current status in relation to the variability in field water availability, soil fertility, farm crop management practices and grain yield throughout Savannakhet province were quantified, first by collecting farm data from 53 and 48 farmers’ fields in the 2007 and 2008 cropping seasons, respectively, These farms were selected to be representative of a wide range of soil and climate conditions within the province. The results show that rainfall distribution pattern, soil type and toposequence position of paddy fields, are crucial factors contributing to the temporal variation in field water availability. The overall yield loss due to water stress associated with late season drought was estimated to be rather small (10%, 5% and 3% for the top, middle and bottom toposequence positions of rice fields, respectively) in the 2008 wet season. On the other hand, application of chemical fertilizer has a large effect on final grain yield, with 50 kg N ha-1 and 30 kg P2O5 ha-1 increasing yield by 600 to 800 kg and 800 to 1000kg ha-1 respectively, in the 2007 and 2008 cropping seasons. A new soil water balance (SWB) model that incorporates the effect of low soil clay content on deep percolation, was developed to quantify field water availability and the length of growing period (LGP) for various rainfall lowland rice cropping environments. The model estimates the amount of water stored in a soil profile, the profile being divided into two layers: Layer 1 (0-200 mm) consists of standing water and the topsoil layer, while Layer 2 (200-1000 mm) is the subsoil layer. The SWB model was validated with field experimental data obtained in the 2002 and 2008 cropping seasons. The simulated free water levels were close to those recorded for the observed field data, with a small mean average error, lower root mean square error, and significant correlation coefficient and index of agreement over all sites across the three toposequence positions of paddy fields. Maps of the length, start and end of growing period (LGP, SGP and EGP, respectively) for rainfed lowland rice in Savannakhet province, were developed using the SWB model, with inputs of median weekly climatic data and soil water characteristics. The province was delineated into three main LGP zones with a short LGP zone (less than 21 weeks) in the east, northwest and some rice fields in the south-western corner of the province; an intermediate LGP zone (21 to 24 weeks) was defined in the central and western part of the province; and a long LGP zone (greater than 24 weeks) for the south and for some rice fields in the western part of the province. The variation in the SGP from year-to-year was due largely to the variation in rainfall early in the wet-season (e.g. April), while EGP was strongly dependent upon the clay content of the soils being cropped. The SWB model was combined with other models that estimate yield potential, soil nutrient supply and yield reduction by low soil water level, to characterize and map the suitability zones for rainfed lowland rice in Savannakhet province. The overall results of the model performance on yield estimates were satisfactorily, with a significant correlation coefficient (0.54**) and high index of agreement (0.68) over the 2007 and 2008 seasons. The model classified three main rice agro-ecological zones according to the suitability of climate and soil conditions. The majority of the lowland rice growing areas are classified as moderately suitable to marginally suitable, while the potential area classified as being high suitable is very small. A large potential response of rice yields to fertilizer inputs is predicted for most of rice growing areas in the province. The best sowing time for achieving a high yield, as evaluated by the model, is the first half of June. Appropriate crop phenology and increasing fertilizer use efficiency that matches with water availability and soil conditions in each rice agro-ecological zone, are important in achieving improvements in rice productivity, as substantial improvements in rice fields cannot be achieved by improving water availability alone, where paddy fields are dominated by soils with low level of indigenous fertility. Although the model is capable of quantifying field water availability and crop yield due to the limitations associated with low levels of soil nutrients and water stress, the model has the potential for further improvements in two areas. First, the estimates of water loss need to be modified by incorporating variable factors such as slope of paddy field, which can affects lateral water movement and hence free water level. Second, the model should incorporate some key agronomic variables, such as internal efficiencies and recovery efficiencies of applied fertilizer, which depend on variety, crop management and climatic conditions, and these factors can be modelled.

Drought and poor soil fertility are often cited as major constraints to rainfed lowland rice production in Laos, particularly in the central and southern parts of the country, where uncertainty in the growing season is common, due mainly to a combination of unreliable rainfall and coarse textured soils with a low water holding capacity and high rates of deep percolation. The soil conditions, together with fluctuations in rainfall distribution, are regarded as the most serious constraints to achieving high and stable grain yields in the rainfed lowland rice ecosystem in this region. Improvements in rainfed lowland rice productivity depend, in part, on improved predictions of water availability, as well as better understanding of soil nutrient and water stress limitations to grain yield. The use of a soil water balance model, in conjunction with the quantification of soil nutrient availability, can help in estimating free water levels in the rice fields, thereby helping determine the duration of the growing period, as well as, helping with predictions of potential yield reduction due to water stress and soil nutrient limitations. Linking the simulated results with Geographic Information System (GIS) can help quantify the spatial pattern of these attributes at a provincial or regional scale. This study was aimed at quantifying the spatial distribution of water availability, including the frequency and severity of water stress development during the growing period, and to estimate the effects of soil fertility and water stress on rice productivity in Savannakhet province in southern Lao PDR. The current status in relation to the variability in field water availability, soil fertility, farm crop management practices and grain yield throughout Savannakhet province were quantified, first by collecting farm data from 53 and 48 farmers’ fields in the 2007 and 2008 cropping seasons, respectively, These farms were selected to be representative of a wide range of soil and climate conditions within the province. The results show that rainfall distribution pattern, soil type and toposequence position of paddy fields, are crucial factors contributing to the temporal variation in field water availability. The overall yield loss due to water stress associated with late season drought was estimated to be rather small (10%, 5% and 3% for the top, middle and bottom toposequence positions of rice fields, respectively) in the 2008 wet season. On the other hand, application of chemical fertilizer has a large effect on final grain yield, with 50 kg N ha-1 and 30 kg P2O5 ha-1 increasing yield by 600 to 800 kg and 800 to 1000kg ha-1 respectively, in the 2007 and 2008 cropping seasons. A new soil water balance (SWB) model that incorporates the effect of low soil clay content on deep percolation, was developed to quantify field water availability and the length of growing period (LGP) for various rainfall lowland rice cropping environments. The model estimates the amount of water stored in a soil profile, the profile being divided into two layers: Layer 1 (0-200 mm) consists of standing water and the topsoil layer, while Layer 2 (200-1000 mm) is the subsoil layer. The SWB model was validated with field experimental data obtained in the 2002 and 2008 cropping seasons. The simulated free water levels were close to those recorded for the observed field data, with a small mean average error, lower root mean square error, and significant correlation coefficient and index of agreement over all sites across the three toposequence positions of paddy fields. Maps of the length, start and end of growing period (LGP, SGP and EGP, respectively) for rainfed lowland rice in Savannakhet province, were developed using the SWB model, with inputs of median weekly climatic data and soil water characteristics. The province was delineated into three main LGP zones with a short LGP zone (less than 21 weeks) in the east, northwest and some rice fields in the south-western corner of the province; an intermediate LGP zone (21 to 24 weeks) was defined in the central and western part of the province; and a long LGP zone (greater than 24 weeks) for the south and for some rice fields in the western part of the province. The variation in the SGP from year-to-year was due largely to the variation in rainfall early in the wet-season (e.g. April), while EGP was strongly dependent upon the clay content of the soils being cropped. The SWB model was combined with other models that estimate yield potential, soil nutrient supply and yield reduction by low soil water level, to characterize and map the suitability zones for rainfed lowland rice in Savannakhet province. The overall results of the model performance on yield estimates were satisfactorily, with a significant correlation coefficient (0.54**) and high index of agreement (0.68) over the 2007 and 2008 seasons. The model classified three main rice agro-ecological zones according to the suitability of climate and soil conditions. The majority of the lowland rice growing areas are classified as moderately suitable to marginally suitable, while the potential area classified as being high suitable is very small. A large potential response of rice yields to fertilizer inputs is predicted for most of rice growing areas in the province. The best sowing time for achieving a high yield, as evaluated by the model, is the first half of June. Appropriate crop phenology and increasing fertilizer use efficiency that matches with water availability and soil conditions in each rice agro-ecological zone, are important in achieving improvements in rice productivity, as substantial improvements in rice fields cannot be achieved by improving water availability alone, where paddy fields are dominated by soils with low level of indigenous fertility. Although the model is capable of quantifying field water availability and crop yield due to the limitations associated with low levels of soil nutrients and water stress, the model has the potential for further improvements in two areas. First, the estimates of water loss need to be modified by incorporating variable factors such as slope of paddy field, which can affects lateral water movement and hence free water level. Second, the model should incorporate some key agronomic variables, such as internal efficiencies and recovery efficiencies of applied fertilizer, which depend on variety, crop management and climatic conditions, and these factors can be modelled.