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.     

The Effects of Different Nitrogen and Phosphorus Rates on Some Quality Traits of Potato

This study was conducted to determine the effects of nitrogen (0, 120, and 240 kg N ha⁻¹) and phosphorus (0, 90, and 180 kg P₂O₅ ha⁻¹) doses on some tuber quality traits of the potato cultivar Agria under the ecological conditions of Erzurum in the years 2005 and 2006. The effects of N levels were significant only on the protein content of tubers while the P levels only significantly affected the oil content of the crisps. No significant N × P interaction effects were found on any of the traits evaluated. Based on these results, it could be concluded that the potato crop should be fertilized with 120 kg ha⁻¹ N and that phosphorus fertilizers should be added when soils are P deficient in the Erzurum region.     

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.     

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.     

The effect of physiological age and planting date on the response of potatoes to applied nitrogen and on levels of residual nitrogen post-harvest

Summary Experiments were conducted on sandy and deep silty soils to assess the effect of physiological age of seed tubers and planting date on the response of potatoes to nitrogen fertiliser. Nitrogen optima commonly had large standard errors which made interpretation of the data difficult. On the sandy soil with cv. Record, early planting increased yield in two years but had no effect on mean N optimum (303 kg ha⁻¹, NOpt). Mean NOpt was less on the silty soil where the cv. Pentland Squire was grown, and was reduced from 273 kg ha⁻¹ to 241 kg ha⁻¹ when planting was delayed by 4 weeks. Physiological age had no effect on NOpt. On the sandy soil, residual soil mineral nitrogen (RSMN) increased by 0.05 kg ha⁻¹ per kg N fertiliser applied; on the silty soil the increase was four times as large. RSMN was larger following the late planted crop on the silty soil in one year.     

Rice yield and its relation to root growth and nutrient-use efficiency under SRI and conventional cultivation: an evaluation in Madagascar

While plant growth and productivity are known to derive from the interaction between genetic potential (G) and environmental factors (E), efforts to improve rice production have usually proceeded assuming a standard E that is created by conventional rice-growing practices. Genotypes have been assessed for their performance in continuously flooded paddy soils, with optimally dense plant populations, with reliance on inorganic fertilization to raise yields. The System of Rice Intensification (SRI) developed in Madagascar and now becoming accepted in much of Asia proposes that GxE interactions can be made more productive with different management practices: optimally sparse populations, established with very young seedlings carefully transplanted, intermittent flooding of paddies, with active soil aeration and with soil organic matter enhanced as much as possible. This article evaluates the effects of alternative SRI cultural practices on grain yield with particular attention to their impact on the growth and functioning of rice plant roots and on associated nutrient-use efficiencies that could be contributing to the observed higher grain yields. On-station experiments and on-farm surveys were conducted in Madagascar to evaluate SRI practices in comparison with standard cultural methods, considering how rice plants’ expression of their genetic potential was affected by different crop management practices. Controlling for both soil and farmer effects, rice plants cultivated with SRI methods produced average yields more than double those from standard practice (6.26 vs. 2.63 t ha⁻¹). The most evident phenotypic difference was in plant root growth, assessed by root-pulling resistance (RPR), a summary measure of root system development. On average, uprooting single SRI plants required 55.2 kg of force plant⁻¹, while pulling up clumps of three conventionally grown plants required 20.7 kg hill⁻¹, or 6.9 kg plant⁻¹. SRI plants thus offered 8 times more resistance per plant to uprooting. Direct measurements confirmed that SRI methods induced both greater and deeper root growth, which could be contributing to increased nutrient uptake throughout the crop cycle, compared with the shallower rooting and shorter duration of root functioning under continuous flooding. Rice plants grown with SRI methods took up more macronutrients than did the roots of conventionally managed plants, which was reflected in the higher SRI yields. When grain yield was regressed on nutrient uptake to assess nutrient-use efficiency, SRI plants achieved higher grain yield per unit of N taken up, compared to plants grown with conventional methods. The internal efficiency (IE) of SRI plants in utilizing macronutrients was 69.2 for N, 347.2 for P, and 69.7 for K, while the IE in plants conventionally grown was 74.9, 291.1, and 70.4 for these three macronutrients, respectively. Although no significant differences in IE were observed for N and K, the uptake of P was significantly greater, indicating more efficient use of P by SRI plants for grain production. More research needs to be done on such relationships, but this study indicates that productive changes in the structure and functioning of rice plants, particularly their roots, can be induced by alternative management methods.     

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.     

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.     

Effect of fertilization on crop responses and solute transport for rice crop in a sub-humid and sub-tropical region

In order to increase the efficacy of water and control the losses of fertilizer, it is necessary to assess the influence of level of fertilization on crop responses, movement and balance of water and solutes from fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization on crop responses and fertilizer solute transport in rice crop field in a sub-humid and sub-tropical region. Field experiment was conducted on rice crop (cultivar IR 36) during the years 2003, 2004, and 2005. The experiment included four fertilizer treatments comprising different levels of fertilizer application. The fertilizer treatments during the experiment were: F₁ = control with N:P₂O₅:K₂O as 0:0:0 kg ha^?1; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha^?1; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha^?1 and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha^?1. The results of the investigation revealed that the magnitudes of crop parameters such as grain yield, straw yield, and maximum leaf area index increased with increase in fertilizer application rate. The levels of fertilization had very little effect on water loss via deep percolation and water use by the crop. The levels of fertilization had considerable effect on N leaching loss and uptake of N whereas it had no significant impact on leaching loss of water-soluble phosphorus. This indicated that PO₄-P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. The results also revealed that increase in level of fertilization increased water use efficiency considerably by increased crop yield. From the observed data of nutrient use efficiency, crop yield and environmental pollution, the fertilization rate of N:P₂O₅:K₂O as 80:40:40 kg ha^?1 (F₂) was the most suitable fertilizer treatment for rice crop among studied treatments.     

Mass balance analysis in Korean paddy rice culture

A field experimental study was performed during the growing season of 2001 to evaluate water and nutrient balances in paddy rice culture. Three plots of standard fertilization (SF), excessive fertilization (EF, 150% of SF), and reduced fertilization (RF, 70% of SF) were used and the size of treatment plot was 3,000 m², respectively. The hydrologic and water quality was field monitored throughout the crop stages. The water balance analyses indicated that approximately half (47–54%) of the total outflow was lost through surface drainage, with the remainder consumed by evapotranspiration. Statistical analysis showed that there was no significant effect of fertilization rates on nutrient outflow through the surface drainage or rice yield. Reducing fertilization of rice paddy may not work well to mitigate the non-point source nutrient loading in the range of normal farming practices. Instead, the reduction in surface drainage could be important to controlling the loading. Suggestive measures that may be applicable to reduce surface drainage and nutrient losses include water-saving irrigation by reducing ponded water depth, raising the weir height in diked rice fields, and minimizing forced surface drainage as recommended by other researchers. The suggested practices can cause some deviations from conventional farming practices, and further investigations are recommended.     

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.     

Influence of applied nitrogen on potato part I: Yield,quality, and Nitrogen uptake

Fertilizer nitrogen (N) may be managed to increase crop production and profitability while reducing nitrate contamination of groundwater. A two-year field investigation was conducted to evaluate the effects of applied N on tuber yield and quality, dry matter production and N uptake of potato (Solanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as ammonium sulfate [(NH₄)₂SO₄] at rates of 0, 56 and 112, kg N ha^?1 in a single application at planting or 112 and 168 kg N ha^?1 in split applications during the growing season. Total tuber yield generally increased with N applications up to 112 kg N ha^?1. Only one of the three experimental sites showed an increase in marketable tuber yield when 112 kg N ha^?1 was split evenly between planting and tuber initiation. Tuber specific gravity was not affected by N rate. Nitrogen rates of 112–168 kg N ha^?1 maximized dry matter production and plant tissue N concentration at onset of maturity and harvest. Tuber N concentration at harvest ranged from 13–17 g kg^?1 at two of the three locations. Values for the third experiment were 10–13 g N kg^?1. Whole crop N uptake at onset of senescence ranged from 45 to 225 kg N ha^?1 across all locations and treatments. An average of 67 percent of this N was found in tubers at harvest. Nitrogen fertilization exceeded N removal in harvested tubers by more than 50 kg N ha^?1 only for the 168 kg N ha^?1 treatment. These results indicate that acceptable tuber yield can be obtained with lower N rates than those currently used by most producers, with the potential for reducing net loss of N from the soil.     

Phosphorus Balance and Soil Phosphorus Status in Paddy Rice Fields with Various Fertilizer Practices

Abstract

Excess phosphorus (P) has accumulated in Japanese paddy soils, due to fertilizer P inputs over crop requirement for several decades, and improvement of the excess of P is necessary in view of environmental conservation. This study aimed to evaluate the input/output balance of P related to soil P status in paddy rice systems, and to obtain a practical indication. Irrigated rice (Oryza sative L.) was cultivated on a gley soil from 1997 to 2006. Six field plots fertilized with commercial fertilizer, animal waste composts, green manure and none were included. Phosphorus input varied among plots from 0 to 73 kg ha-¹ yr-¹. Rice P uptake was approximately 20 kg ha-¹, indicating no response to the P input. This was attributed to a large amount of plant-available Bray- and Truog-P in our soils. In our fields, paddy rice could be cultivated with no P-containing fertilizer or amendment. As a result, increase in the P input led to an increase in partial P balance (PPB). Cumulative increase in PPB resulted in the increase in soil total P, whereas cumulative decrease of PPB tended to decrease it. Excess accumulation of the soil P results in a loss of P into the environment. We concluded that P fertilization should be restricted to 20 kg ha-¹ yr-¹ (corresponding to 46 kg ha-¹ yr-¹ as P₂O₅), based on evenly balanced P input with the rice P uptake. It is also important to include all of the P-containing fertilizers and amendments when determining the amount of application.     

Fertilizer management impacts on stand establishment, disease, and yield of Irish potato

Summary Excessive fertilizer application in North Carolina, USA results in high residual soil levels of P, K and total soluble salts in potato fields. Our objectives were to determine the salt sensitivity of three common cultivars (Atlantic. Snowden and Superior), and the effects of planting density and fertilization on stand establishment, soilborne disease, and yield. Greenhouse results suggest that potato growth and emergence, but not shoot initation, are reduced by high salinity. On a Portsmouth fine sandy loam, high fertilizer rates did not reduce stands of cv. Atlantic in the field in 1996 or 1997. Excess N resulted in moreRhizoctonia stem canker in 1996, and lower yields at the lower planting density in 1997. Yield compensation for reduced plant density occurred in 1997 at the lower N rates (56 and 112 kg N ha⁻¹) and at the high PK rate (49 kg P and 139 kg K ha⁻¹).     

The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants

Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha⁻¹. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)⁻¹ whereas starch from plants grown with 30 kg P ha⁻¹ contained 20.6 nmol P (mg starch)⁻¹. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l⁻¹, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.     

Influence of irrigation frequency on greenhouse gases emission from a paddy soil

Water management is known to be a key factor on methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) emissions from paddy soils. A field experiment was conducted to study the effect of continuous irrigation (CI) and intermittent irrigation (II) on these emissions. Methane, CO₂, and N₂O emissions from a paddy soil were sampled weekly using a semi-static closed chamber and quantified with the photoacoustic technique from May to November 2011 in Amposta (Ebro Delta, NE Spain). Intermittent irrigation of rice paddies significantly stimulated (N₂O + N₂)–N emission, whereas no substantial N₂O emission was observed when the soil was re-wetted after the dry phase. The cumulative emission of (N₂O + N₂)–N was significantly larger from the II plots (0.73 kg N₂O–N ha^?1 season^–1, P < 0.05) than from the CI plots (?1.40 kg N₂O–N ha^?1 season^?1). Draining prior to harvesting increased N₂O emissions. Draining and flooding cycles controlled CO₂ emission. The cumulative CO₂ emission from II was 8416.35 kg CO₂ ha^?1 season^?1, significantly larger than that from CI (6045.26 kg CO₂ ha^?1 season^?1, P < 0.05). Lower CH₄ emission due to water drainage increased CO₂ emissions. The soil acted as a sink of CH₄ for both types of irrigation. Neither N₂O–N nor CH₄ emissions were affected by soil temperature. Global warming potential was the highest in II (4738.39 kg CO₂ ha^?1) and the lowest in CI (3463.41 kg CO₂ ha^?1). These findings suggest that CI can significantly mitigate the integrative greenhouse effect caused by CH₄ and N₂O from paddy fields while ensuring the highest rice yield.     

Plant and soil responses to nitrogen and phosphorus fertilization of bromegrass‐dominated haylands in Saskatchewan,Canada

Field experiments were conducted at three different sites in Saskatchewan, Canada (Colonsay, Vanscoy and Rosthern) over two years (2005 and 2006) to determine the effects of dribble‐banded and coulter‐injected liquid fertilizer applied in the spring of 2005 at 56, 112 and 224 kg N ha^?1 with and without P at 28 kg P₂O₅ ha^?1. The three sites were unfertilized, 7‐ to 8‐year old stands of mainly meadow bromegrass (Bromus riparius)‐dominated haylands. All fertilization treatments produced significantly (P ≤ 0·05) higher dry matter yield than the control in the year of application at the three Saskatchewan sites. There was no significant difference between the two application methods (surface dribble band vs. coulter injected) for any fertilizer treatments. The addition of 28 kg P₂O₅ ha^?1 P fertilizer along with the N fertilizer did not have a significant effect on yield in most cases. In the year of application, increasing N rates above 56 kg N ha^?1 did not significantly increase yield over the 56 kg N ha^?1 rate in most cases, but did increase N concentration, N uptake and protein concentration. A significant residual effect was found in the high N‐rate treatments in 2006, with significantly higher yield and N uptake. In 2005, the forage N and P uptake in the fertilized treatments were significantly higher than the control in all cases. The N uptake at the three Saskatchewan sites increased with increasing N rate up to the high rate of 224 kg N ha^?1, although the percent recovery of applied N decreased with increasing rate. The P fertilization with 28 kg P₂O₅ ha^?1 also increased P uptake. Overall, rates of fertilizer of approximately 56 kg N ha^?1 appear to be sufficient to produce nearly maximum forage yield and protein concentration of the grass in the year of application.     

Impact and Interaction of Nitrogen and Phytophthora infestans as Yield-limiting and Yield-reducing Factors in Organic Potato (Solanum tuberosum L.) Crops

For organic potato producers, the two main challenges are disease and nutrient management. Both are limited by regulations that on the one hand prohibit the use of chemical fertilizers, especially nitrogen, and on the other hand prohibit most synthetic pesticides. Late blight caused by Phytophthora infestans is commonly thought to be the most yield-reducing factor. However, because there is no really effective fungicide available to control late blight, there are virtually no yield loss data available for organic farming conditions. In this paper, the state of the art of organic potato tuber growth under on-farm conditions with respect to disease and nutrient management is summarized by field trials and on-farm surveys on commercial organic crops carried out in the years 1995–1998. Soil nitrogen (N) levels, plant N uptake, disease development of P. infestans and potato yield were measured. Results indicated that N availability was most important in limiting yields in organic potato crops. From on-farm data, a model including disease development, growth duration of the crops until foliage decay and different parameters related to N status of the crop could explain 73% of the observed variation in yield. Only 25% of this variation in yield could be attributed to the influence of late blight. Differences in N availability explained 48%. In conclusion, several points emerged from the results. In organic farming, yields are mainly limited by nutrient availability in spring and early summer. The effects of late blight on yields may often be overestimated and cannot be deduced from results in conventional farming because of the strong interaction with nutrient status. Depending on N availability, tubers stop growing between mid-July (70–90 kg N ha⁻¹ uptake), the end of July (110–140 kg N ha⁻¹ uptake) and mid-August (140–180 kg N ha⁻¹ uptake) due to N limitations. The higher the N status of a potato crop, the longer the growing period needed to achieve the attainable yield and the higher the probability that late blight stops further tuber growth and becomes the key tuber-yield-limiting factor. In the second part of this paper, the interactive effects of soil N availability and the impact of P. infestans on yield in the presence and absence of fungicides from 1996 to 1998 for mid-early main crops are reported. An empirical schematic model of disease impact depending on N availability was developed.     

Improving Yield and Quality of Processing Potato Crops Grown in the Argentinian Pampas: the Role of N,P and S and Their Impact on CO<Subscript>2</Subscript> Emissions

The area grown with processing potato crops in the Argentinian Pampas has been increasing steadily since 1995. The aim of this work was to assess the effects of N, P and S upon yield and tuber quality and their impact on CO₂ emissions assessed with the Cool Farm Tool-Potato. During the spring-summer growing seasons 2008/2009 and 2009/2010, ten fertilization experiments to individually assess N, P and S effects were carried out in the southeast region of the Argentinian Pampas. Nitrogen (four N rates), phosphorus (four P rates) and sulfur (three S rates) were applied at planting and tuber initiation; at combined rates of 0, 50, 100 and 150 kg N ha^?1, and at rates of 0, 25, 50 and 100 kg P ha^?1 and 0, 10 and 20 kg S ha^?1. N and P had a positive effect on total tuber yield, but tuber dry matter concentration (DMC) decreased at higher N rates. The fraction of marketable tubers suitable for processing into French fries increased with the addition of N, showed no variations with P fertilization, and decreased when S was applied. French fry colour, length/width (L:W) ratio and tuber defects were not affected by N, P and S fertilization. With regard to CO₂ emissions assessed with the Cool Farm Tool-Potato, results showed that the higher the N rates the higher the CO₂ emissions, but they decreased at higher yields. P and S rates did not have an impact on the CO₂ emissions, which also decreased at higher yields. Under the production system of the Pampas, N should be split between planting and tuber initiation, and intermediate P rates should be applied all at planting, in order to improve crop yield and quality and to reduce CO₂ emissions.     

Evaluation of N and P mass balance in paddy rice culture along Kahokugata Lake, Japan, to assess potential lake pollution

Kahokugata Lake, a closed lake, has been subject to eutrophication. This research was conducted to clarify the actual phenomena and evaluation of the discharges of N and P from paddy test fields in the lowlands into Kahokugata Lake. A comprehensive mass balance of N and P was obtained from 4 years of study. About N, the mean value of harvested unhulled rice (79.9 kg/ha) was greater than mean controlled release fertilizer inputs (56.7 kg/ha). Other inputs and outputs include N in atmospheric acid deposition (21.4 kg/ha) and N fixation–denitrification (9.2 kg/ha). The rice straw recycled after harvest was balanced by straw produced in the succeeding year. The runoff and percolation losses discharged into the lake was 11.3 kg/ha, (8.6% of total inputs). Since the rice harvested was consumed domestically, which taking out from the farmland and, therefore, nitrogen pollutant into the lake was becoming small, paddy rice at this site is considered an “anti-polluting, purifying or cleansing” crop. The P content in harvested rice (39.4 kg/ha) was balanced by fertilizer inputs (36.4 kg/ha). Previous studies examining inflow–outflow relationships without considering a comprehensive mass balance may lead to erroneous conclusions. Our findings indicate paddy rice in lowlands could be an environmentally friendly crop and can play an important role in reducing pollution of lakes, and therefore should be considered in land use planning.