Surface and subsurface losses of N and P from salt-affected rice paddy fields of Saemangeum reclaimed land in South Korea

The present study was carried out to evaluate nutrient losses that occur during the course of agricultural activity from rice paddy fields of reclaimed tidal flat. For this study, we chose a salt-affected rice paddy field located in the Saemangeum reclaimed tidal area, which is located on the western South Korean coasts. The plot size was 1,000 m² (40 m × 25 m) with three replicates. The soil belonged to the Gwanghwal series, i.e., it was of the coarse silty, mixed, mesic type of Typic Haplaquents (saline alluvial soil). The input quantities of nitrogen and phosphorus (as chemical fertilizer) into the experimental rice paddy field were 200 kg N ha⁻¹ and 51 kg P₂O₅ ha⁻¹ per annum, and the respective input quantities of each due to precipitation were 9.3–12.9 kg N ha⁻¹ and 0.4–0.7 kg P ha⁻¹ per annum. In terms of irrigation water, these input quantities were 4.5–8.2 kg N ha⁻¹ and 0.3–0.9 kg P ha⁻¹ per annum, respectively. Losses of these nutrients due to surface runoff were 22.5–38.1 kg N ha⁻¹ and 0.7–2.2 kg P ha⁻¹ for the year 2003, and 26.8–29.6 kg N ha⁻¹ and 1.6–1.9 kg P ha⁻¹ for the year 2004, respectively. Losses of these nutrients due to subsurface infiltration during the irrigation period were 0.44–0.67 kg N ha⁻¹ and 0.03–0.04 kg P ha⁻¹ for the year 2003, and 0.15–0.16 kg N ha⁻¹ and 0.05–0.06 kg P ha⁻¹ for 2004. When losses of nitrogen and phosphorus were compared to the amount of nutrients supplied by chemical fertilizers, it was found that 11.3–19.1% of nitrogen and 0.5–1.7% of phosphorus were lost via surface runoff, whereas subsurface losses accounted to 0.2–0.8% for nitrogen and only 0.02–0.04% for phosphorus during the 2-year study period.     

Environmental multifunctionality of Indonesian agriculture

Industrial and urban developments in Indonesia focus on the economic merits, but neglect agricultural services that, when disappear, will destabilize the environmental and livelihood systems. A series of 5-year study has evaluated various aspects of multifunctionality and implications of paddy field conversion on the disappearance of multifunctionality. Soil loss from a series of 18 terraced paddy fields in central Java is negligible. Only a few terraces located along the streams directly caused sedimentation. The functions of flood mitigation, water-resource conservation, erosion reduction, organic waste disposal, heat mitigation, and rural amenity of paddy fields in Citarum watershed in West Java were significant. The ‘replacement costs’ of such functions was about 51% ($92.67 million yr⁻¹) of the total price of rice of $181.34 million yr⁻¹ produced in the 156,000 ha paddy field. This amount could be considered as free services by the farmers to the society. However, because of society's negligence and unawareness, conversion has been accelerating while development of new paddy fields has been decelerating in the last few years. Low and fluctuating price of agricultural products, unavailability or non-affordability of agricultural supplies and inaccessibility to market are among the major disincentives faced by farmers. Because of appreciable multifunctionality they produce, farmers deserve various incentives for the sake of environmental sustainability and other services.     

Spatial variation of infiltration rate and compactness in paddy fields

Percolation loss of water in rice fields is a major cause of low water use efficiency. Variation of infiltration rate and soil compactness in four paddy fields (with clay, silty clay, clay loam, and loam textures) was investigated in northern Iran. In each field, in longitudinal and transverse directions, points located 0.5, 2.5, 6.5, 12.5, … m from the bunds were selected and water infiltration rate and resistance to penetration of a pocket penetrometer were measured. The results showed that in clay soil, average final infiltration rate (f _c) in longitudinal direction, transverse direction, and center of the field was 0.216, 0.136, and 0.08 cm day⁻¹, respectively. The f _c for loamy soil was 2.77, 2.32, and 0.409 cm day⁻¹, respectively. Similar differences were observed in the other two soil textures. In general, effect of direction of the field for measuring infiltration rate was not statistically significant. Loam and clay loam soils, with resistance to penetration of 0.37 and 0.33 kg cm⁻², were not significantly different. But, clay and silty clay soils with resistance to penetration of 0.25 and 0.14 kg cm⁻² were significantly different (P < 0.05). Resistance to penetration of the penetrometer was not affected significantly (P < 0.05) by direction of measuring this parameter in the field. The conclusion is that if measured soil physical properties in a paddy field are going to be representative of the whole field, they should be measured at different locations, especially near the bunds. Another strategy for obtaining a representative infiltration rate or compactness for a paddy field is uniform puddling of the field.     

Convective velocity of ponded water in the vegetated paddy lysimeter

Ponded water convection kinetics should be altered by growth stages of rice plants. We investigated the convective velocity of ponded water in a vegetated paddy field. The convective velocity was measured using the equipment through use of the principle of a hot-wire anemometer, and the temperature profile of the ponded water was measured using lysimeters with and without paddy rice vegetation. The maximum convective velocity in a vegetated plot was 0.7 mm s⁻¹, slower than the maximum velocity in an unvegetated plot, which was 1.6 mm s⁻¹. The convective velocity in a vegetated plot increased slightly when the temperature of the surface water was higher than that near the soil, between 09:00 and 17:00.     

Accumulation of arsenic and its distribution in rice plant (Oryza sativa L.) in Gangetic West Bengal, India

The presence of arsenic in irrigation water and in paddy field soil were investigated to assess the accumulation of arsenic and its distribution in the various parts (root, straw, husk, and grain) of rice plant from an arsenic effected area of West Bengal. Results showed that the level of arsenic in irrigation water (0.05–0.70 mg l⁻¹) was much above the WHO recommended arsenic limit of 0.01 mg l⁻¹ for drinking water. The paddy soil gets contaminated from the irrigation water and thus enhancing the bioaccumulation of arsenic in rice plants. The total soil arsenic concentrations ranged from 1.34 to 14.09 mg kg⁻¹. Soil organic carbon showed positive correlation with arsenic accumulation in rice plant, while soil pH showed strong negative correlation. Higher accumulation of arsenic was noticed in the root (6.92 ± 0.241–28.63 ± 0.225 mg kg⁻¹) as compared to the straw (1.18 ± 0.002–2.13 ± 0.009 mg kg⁻¹), husk (0.40 ± 0.004–1.05 ± 0.006 mg kg⁻¹), and grain (0.16 ± 0.001–0.58 ± 0.003 mg kg⁻¹) parts of the rice plant. However, the accumulation of arsenic in the rice grain of all the studied samples was found to be between 0.16 ± 0.001 and 0.58 ± 0.003 mg kg⁻¹ dry weights of arsenic, which did not exceed the permissible limit in rice (1.0 mg kg⁻¹ according to WHO recommendation). Two rice plant varieties, one high yielding (Red Minikit) and another local (Megi) had been chosen for the study of arsenic translocation. Higher translocation of arsenic was seen in the high yielding variety (0.194–0.393) compared to that by the local rice variety (0.099–0.161). An appreciable high efficiency in translocation of arsenic from shoot to grain (0.099–0.393) was observed in both the rice varieties compared to the translocation from root to shoot (0.040–0.108).     

Export rate of dissolved organic matter from paddy fields during cultivation-activity events

The aim of this study is to quantify the dissolved organic carbon (DOC) of drainage water from paddy fields in agricultural areas of Tottori prefecture, Japan. In four experimental paddy fields, DOC concentration varied much from 1.1 to 10.1 mg C l⁻¹, and was the highest during heavy runoff that occurred in April when there was a non-agricultural period. However, variation in DOC concentration did not always correspond to rainfall, but depended more on cultivation-activity events such as tilling, planting, draining in summer, and final draining in autumn. The water discharge rate from each experimental field was estimated by using a hydrologic model (the Tank Model and a genetic algorithm). Daily DOC export rate per unit area of three experimental paddy fields was calculated to be 0.0074, 0.0052, and 0.0081 kg a⁻¹ day⁻¹, respectively. The daily DOC export rate showed large seasonal variation with the highest value in May and June. It can be concluded that DOC export from paddy fields can be a substantial source of DOC in receiving waters, and the export rate depends much on cultivation method practice. It might be suggested that DOC export from paddy fields can be controlled by a better water management practice of farmers.     

Economic valuation of cultivated lands as nitrogen removal/effusion sites by newly proposed replacement cost method

To valuate the multifunctionality economically is effective to make it possible to realize the value for the nation and to compare functionalities among countries of the world. In this paper, the external economies of paddy fields and fallow paddy fields including wetlands as N removal function sites, and of upland fields and orchards as pollution sites are valuated by the newly proposed replacement cost method, by replacing them with construction costs of water quality improvement facilities. In addition, we discuss an agricultural land-use scenario in which cultivated land has no net negative economic effect on the water environment. The results showed that (1) paddy fields and fallow paddy fields including wetlands were respectively valued at 1.2×10³ and 2.81×10³ JPY m⁻² on average as the N removal sites, (2) upland fields had 0.32×10³ JPY m⁻² on average of economic value, and suggested that paddy fields have an external economic value that compensates for the negative external economic value of upland fields 3.65 times their size.     

Fertilization management of paddy fields in Piedmont (NW Italy) and its effects on the soil and water quality

The fertilization management of the rice crop in Piedmont was analyzed at a regional scale, and the agronomic and environmental sustainability of the actual fertilization strategy of rice was evaluated through the analysis of its effect on the soils and waters quality. On average, a total amount of 127 kg ha⁻¹ of N, 67 kg ha⁻¹ of P₂O₅ and 161 kg ha⁻¹ of K₂O were supplied to the rice crop. In most cases N and P fertilization was rather well balanced with crop removal. The N balance was in the range ±50 kg for 77% of the surface. The low concentration of N in the groundwater reflected the small N surplus. P fertilization resulted to be smaller than removal for 53% of the surface. Nevertheless, the soil extractable P was very high, probably because of former higher P inputs. This resulted in a high concentration in water courses and aquifers. The K fertilization was excessive (surplus >100 kg ha⁻¹) for 53% of the surface, but most soils showed a low K content. K is probably contributing to nutrient leaching to a great extent. The average soil organic matter (SOM) content of paddy fields was higher than that of normally-cultivated soils in Piedmont, and the C/N was higher, owing to the low mineralization rate in waterlogged conditions. The SOM content was in relation with the management of the crop residues, as the tradition of burning straw after harvest was still widespread on 65% of the paddy surface.     

Assessment of nitrogen contamination of groundwater in paddy and upland fields

This study aims to assess the nitrogen contamination of groundwater in paddy and upland fields. A reactive chemical transport model PHREEQC and a variable saturated groundwater flow and transport model FEMWATER were used to evaluate the vertical transport of nitrogen compound in various soil types of paddy and upland. The shallow groundwater quality monitoring data of 2003, 2006, 2009 in the Choushui river alluvial fan, the major agriculture production area in Taiwan, were applied to support the validity of the numerical simulation findings. Results from PHREEQC and FEMWATER simulations showed that the organic-rich impermeable plow sole layer underneath the muddy layer of rice paddy can effectively reduce NO₃ ⁻ and N₂ to NH₄ ⁺ and retard the movement of NH₄ ⁺. However, in the upland field which has no plow sole layer, the NH₄ ⁺ can move easily to the shallow aquifer and contaminate the groundwater. The spatiotemporal distribution of NO₃ ⁻–N and NH₄ ⁺–N in the Choushui river alluvial fan revealed that high nitrate–N contamination areas were located mainly in the upland field of the proximal fan, where the granular unconfined aquifer was vulnerable to surface contaminants. Moreover, the unconfined nature of the aquifer allows the oxidization of NH₄ ⁺ to NO₃ ⁻ and accelerates the plume movement. High ammonium–N concentration areas were mostly dispersed in the distal-fan area where upland planting and aquacultural farming were prevailed. The high NH₄ ⁺–N found in the northern Choushui river alluvial fan was attributed to the alternative planting of rice and upland crops, and the plow sole layer was broken to maintain the quick drainage upland crop needs.     

Nitrogen and phosphorus leaching losses from paddy fields with different water and nitrogen managements

While many water-saving rice production techniques have been adopted in China, the environmental effects of these techniques require further investigation. This study aims to assess nitrogen (N) and phosphorus (P) leaching losses under real conditions in different water and N managements. Two water and three N treatments are conducted in the Taihu Lake region of China. Results show that the total N leaching losses during the rice season under flooding irrigation (FI) are 12.4, 9.31, and 7.17 kg ha⁻¹ for farmers’ fertilization practices (FFP), site-specific N management (SSNM), and controlled-release nitrogen fertilizer management (CRN), respectively. Under controlled irrigation (CI), the respective losses were 7.40, 5.86, and 3.79 kg ha⁻¹ for the same management methods. The total P leaching losses during the rice season under FI were 0.939, 0.927, and 0.353 kg ha⁻¹ for FFP, SSNM, and CRN, respectively. Under CI, the losses were 0.424, 0.433, and 0.279 kg ha⁻¹, respectively, for the same management methods. Ammonium and nitrate N accounted for 42.2–65.5% and 11.8–14.7% of the total nitrogen leaching losses under different water and N management methods, respectively. Due to significant decrease of volumes of percolation water and nitrogen and phosphorus concentrations in percolation water, N and P leaching losses were reduced in the CI treatment compared to the FI treatment under the same N management. The reduction of N input and application of controlled-release nitrogen fertilizer can reduce N and P leaching losses from paddy fields.     

Assessment of the long-term variation in the nitrogen pollution load potential from farmland to groundwater in the Tedori River Basin, Japan

The long-term nitrogen pollution load potential (NPLPg) to groundwater from farmlands was examined in the Tedori River Basin. The NPLPg was estimated using the difference between N in the fertilizer application rate and N outputs in crop yield at 5-yearly intervals from 1960 to 2005. The total yearly NPLPg of 1,085 t (103 kg) in the 1960s decreased to 774 t by 1975. Thereafter, the NPLPg gradually increased to 976 t in the 1990s, but decreased again to 369 t in 2005. The NPLPg decreased by 23% for rice and by 37% for horticultural crops from 1960 to 2005 with an overall decrease of 34%. The NPLPg per unit area was relatively stable over time for rice, soybean, barley, and horticultural crops, but there were significant differences among them. The NPLPg for rice ranged from 39 to 85 kg ha⁻¹ year⁻¹ with an average of 65 kg ha⁻¹ year⁻¹ and that of the horticultural crops ranged from 273 to 357 kg ha⁻¹ year⁻¹ with an average of 302 kg ha⁻¹ year⁻¹ The significant long-term changes in the NPLPg suggest that evaluation at a specific point in time is insufficient for an integrated assessment of groundwater pollution.     

Impact of earthen waste storage on nitrate concentration of surface water

In 1992 and 2002, investigations on the water quality and hydrology were carried out in a small agricultural catchment where swine waste was stored in earthen waste storage. The in-stream nitrogen loads and the nitrogen inputs on a sub-catchment scale were estimated and compared between 1992 and 2002. For the entire catchment, the estimated nitrogen inputs increased from 22.5 to 32.9 ton year⁻¹ (from 406 to 594 kg ha⁻¹ year⁻¹), whereas the nitrate nitrogen concentration at the outlet was constant—27 mg l⁻¹. In a sub-catchment (area C) with earthen waste storages, the nitrate nitrogen concentrations at the outlet were high, 42–51 mg l⁻¹. In a sub-catchment (area A) with an earthen waste storage, which was not in service since 1990, although the nitrogen inputs were maintained at 390 kg year⁻¹ (53 kg ha⁻¹ year⁻¹), the nitrate nitrogen concentrations at the outlet decreased from 26 to 4.9 mg l⁻¹. With assuming that the nitrogen transport rates for sources except swine waste are equal to the rates estimated for a sub-catchment without earthen waste storage, the in-stream nitrogen loads for area A were estimated to decrease from 1,334 to 94 kg year⁻¹ and the transport rates for area A were estimated to decrease from 3.95 to 0.73. These results suggest that the effluent from earthen waste storage has affected surface water quality two years after the storage was out of service and its effect largely decreased after a decade.     

Diffusion of oxygen through lenticels in potato tuber

Summary Diffusion into the potato tuber of oxygen for respiration takes place only through lenticels, and not through the rest of the periderm. The number of lenticels which were capable of injection with methylene blue solution was observed to be about 100 per tuber. Rates of oxygen diffusion per lenticel varied from 0.024 to 0.296 cm³ h⁻¹ atm⁻¹ with a mean of 0.1105±0.013 cm³ h⁻¹ atm⁻¹.     

Spatial variability of soil saturated hydraulic conductivity in paddy field in accordance to subsurface percolation

Insufficient puddling with inappropriate implements or imprecise time/intensity may alter saturated water flow in paddy soil spatially or temporary due to change in aggregate size distribution, dry bulk density, saturated hydraulic conductivity, and percolation rate of the soil. In this study, spatial variability of saturated hydraulic conductivity (K _s), a key parameter of the saturated water flow, in Fuchu Honmachi paddy plot (100 m × 28 m) was characterized based on dielectric or ADR dry bulk density (ρ_b-ADR) with help of non-similar media concept (NSMC) and geostatistics model to meet its correlation to subsurface percolation. A 100 cc core and an ADR data were sampled from each sub-plot (7 m × 7.5 m), and then were used for measuring and predicting ρ_b and K _s. The predicted data agreed with the measured ones, in which they fitted well the x = y line with RMSE of 0.029 cm³ cm⁻³ (R ² = 0.68), 0.027 g cm⁻³ (R ² = 0.71) (ρ_b), and 0.098 cm d⁻¹ (R ² = 0.45) for θ, ρ_b, and K _s, respectively. The predicted ρ_b and K _s had similar trend in spatial variability to the measured ones particularly within the distance of 46.3–51.9 m and 26.2–27.9 m, respectively. The spatial variability of the predicted K _s coincided to that of the subsurface percolation rate, in which they had similar distance of dependence. The results indicated that the presenting method can be reasonably accepted.     

Assessment of management of direct seeded rice production under different water conditions in Cambodia

In order to assess direct seeding of rice technology to cope with future agricultural labor shortage in Cambodia, agronomic experiments were conducted in 2005 and 2006 to compare direct seeding with transplanting under three water conditions (non-flooded, shallow flooded, and deep flooded conditions) with/without weed control by herbicides (bentazone and cyhalofop-butyl) for two Cambodian rice varieties (shorter stature and early maturity Sen Pidao, taller stature and longer maturity Phka Rumduol). Average rice yield in 2 years was lower in direct seeding (341 g m⁻²) than transplanting (404 g m⁻²), but interaction components with year, varieties, water conditions, and weed management were significant, and the attained maximum yield of direct seeding (510 and 464 g m⁻² for Phka Rumduol variety in shallow flooded condition with weeding in 2005 and 2006, respectively) was similar to that of transplanting. Plant length and dry weight of rice were reduced in non-flooded and deep flooded conditions compared with shallow flooded condition, and grain yield was the highest in shallow flooded condition. Yield advantage of Phka Rumduol over Sen Pidao increased under direct seeding, particularly under non-flooded conditions in 2005 because weed infestation was more suppressed in Phka Rumduol even without weeding. Increase in 100 g m⁻² of weed infestation prior to heading (dry weight basis) reduced about 20% of attainable yield with weed control. This study identified importance of stature and growth duration of rice varieties and presence of standing water as well as the weed control, in order to develop and extend direct seeding in the Cambodia.     

Recycling of rice straw to improve wheat yield and soil fertility and reduce atmospheric pollution

Burning of rice straw is a common practice in northwest India, where rice–wheat cropping system is extensively followed. The practice results in loss of nutrients, atmospheric pollution and emission of greenhouse gases. A field experiment was conducted at Indian Agricultural Research Institute, New Delhi, India during the rabi season (November to April) of 2002–2003 to evaluate the efficacy of the various modes of rice straw recycling in soil in improving yield and soil fertility and reducing not only carbon dioxide emission but also nitrous oxide (N₂O) emission. The treatment with no rice straw incorporation and application of recommended doses of fertilizer (120, 26 and 50 kg N, P and K ha⁻¹, respectively), gave the highest yield of wheat. Treatments with the incorporation of rice straw at 5 Mg ha⁻¹ with additional amount of inorganic N (60 kg N ha⁻¹) or inoculation of microbial culture had similar grain yields to that of the treatment with no straw incorporation. The lowest yield was recorded in the plots where rice straw was incorporated in soil without additional inorganic N and with manure application. All the treatments with rice straw incorporation had larger soil organic C despite the effect on the mineralisation of soil organic matter. Emission of N₂O was more when additional N was added with rice straw and secondary when straw was added to the soil because of higher microbial activity. The study showed that burning of rice straw could be avoided without affecting yield of wheat crop by incorporating rice straw in soil with an additional dose of inorganic N or microbial inoculation. However, the reduction of N₂O emission due to avoiding burning is in part counterbalanced by an increase in emission during the subsequent wheat cultivation.     

Evaluation of the management practice for controlling herbicide runoff from paddy fields using intermittent and spillover-irrigation schemes

Two water management practices, an intermittent irrigation scheme using automatic irrigation system (AI) and a spillover-irrigation scheme (SI), were compared for the fate and transport of commonly used herbicides, mefenacet (MF) and bensulfuron-methyl (BSM) in experimental paddy plots. Maximum mefenacet concentrations in paddy water were 660 and 540 μg L⁻¹ for AI and SI plot, respectively. The corresponding values for bensulfuron-methyl were 46.0 and 42.0 μg L⁻¹. Dissipation of the herbicides in paddy water appeared to follow the first-order kinetics with half-lives (DT₅₀) of 1.9–4.5 days and DT₉₀ (90% mass dissipation) of 7.8–11.3 days. The AI plot had no surface drainage, hence no herbicide was lost through paddy-water discharge. However, SI plot lost about 38 and 49% of applied mefenacet and bensulfuron-methyl, respectively. The intermittent irrigation scheme using automatic irrigation system with a high drainage gate was recommended to be a best management practice for controlling the herbicide losses from paddy fields. The paddy field managed by spillover-irrigation scheme may cause significant water and herbicide losses depending on the volume of irrigation and precipitation. The water holding period after herbicide application was suggested to be at least 10 days according to the DT₉₀ index.     

Historical Changes in Urban Rice Production Systems in Tokyo,Japan

Abstract

Historical changes in planting area, yield improvements, and production of both paddy and upland rice (Oryza sativa L.) in Tokyo and the whole of Japan from 1877 to 2003 were reviewed. The area of rice in Tokyo was at its peak (17,000 ha) at the beginning of the 20th century but dramatically reduced thereafter except for the period of 1950s, to200 and 30 ha for paddy and upland rice, respectively, in 2003, due to urbanization. After the 1950s, the land-use efficiency rate in Tokyo was reduced from 180 to 100% and rice self-sufficiency rate from 4 to 0.1%. There was historical yield improvement of paddy rice in Tokyo particularly after 1960s in the Southern and Northern Tama regions, but the current yield level in Tokyo (ca. 400 g m-²) is lower than that in the whole of Japan (more than 500 g m-²) eventhough crop damage due to low temperatures is not serious.The reasons were discussed from the viewpoints of (1) less agricultural inputs and agronomic management, (2) declining rice research after the 1970s, (3) higher elevating air temperature(e.g. 1.4°C for the last 40 years), in Tokyo, and (4) yield component differences. Upland rice in Tokyo has a planting area comparable with paddy rice (ca. 7,000 to 8,000 ha) during the 1950s, but yield improvement during the last 50 yearsis not noticeable (ca. 150 g m-²) with no development of cultivars, and with greater fluctuation of crop situation index due to drought compared with paddy rice. This review paper discusses the importance of urban rice production system, along with a proposal of the alternatives.     

Simulation of salt and water movement and estimation of water productivity of rice crop irrigated with saline water

The HYDRUS-ID model was experimentally tested for water balance and salt build up in soil under rice crop irrigated with different salinity water (ECiw) of 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ in micro-lysimeters filled with sandy loam soil. Differences of means between measured (M) and HYDRUS-1D predicted (P) values of bottom flux (Q _o) and leachate EC as tested by paired t test were not found significant at P = 0.05 and a close agreement between RMSE values showed the applicability of the HYDRUS-1D to simulate percolation and salt concentration in the micro-lysimeters under rice crop. Potential ET values of rice as obtained from CROPWAT matched well with model predicted and measured one at all ECiw treatments. The model predicted root water uptake varied from 66.1 to 652.7 mm and the maximum daily salt concentration in the root zone was 0.46, 2.3, 4.5, 6.7, 8.4 and 10.2 me cm⁻³ in 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ ECiw treatments, respectively. The grain production per unit evapotranspiration ( \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} ) value of 2.56 in ECiw of 0.4 dS m⁻¹ treatment declined to 1.31 with ECiw of 2 dS m⁻¹. The \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} reduced to one-fifth when percolation was included in the productivity determination. Similarly, the water productivity in respect of total dry matter production (TDM) was also reduced in different treatments. Therefore, the model predicted values of water balance can be effectively utilized to calculate the water productivity of rice crop.     

Assessment for nitrogen pollution loads from farmland, Japan, by objective yield and standard fertilizer usage

This research proposes an assessment for nitrogen (N) pollution loads potential from farmland, based on comparison of N in objective crop yields with standard fertilizer usage. N in the objective yield was calculated using the “Standard Table of Food Composition in Japan”. Three findings were made by considering yields removed from farmland. First, paddy rice and beans have a low pollution potential, with rice paddies showing a negative pollution potential for N (around −14 kg/ha). Second, almost all vegetable and orchard crops tested had a high pollution potential for N, although this differed from crop to crop. Third, our outcomes align well with farmland pollution potential and non-absorbed nitrogen (NAN) as defined by Nishio, although the latter and indices rely on a laborious and complicated method. The correlation coefficients were 0.745 (R ² = 0.555). These outcomes show the effectiveness of our proposed assessment for potential environmental pollution loads.