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.     

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.     

Analysis of the nitrogen pollution load potential from farmland in the Tedori River Alluvial Fan Areas in Japan

A nitrogen balance study was carried out by setting up a test paddy in order to estimate the nitrogen pollution load potential (NPLP) from farmland in the Tedori River Alluvial Fan Areas and the load from the entire area under consideration was estimated using the cropping record and fertilizer application rate (FAR). The total NPLP was estimated to be 261 tons/year and the load from the paddy 79 tons/year for 5,704 ha, which would translate to an intensity of 14 kg/ha, while the load from the vegetable field was estimated to be 118 tons/year for 215 ha, which would equate to an intensity of 549 kg/ha. The pollution loads for the vegetables were significantly greater than those for the rice. The load for the barley was 57 tons/year for 261 ha (216 kg/ha) and that for the orchards was 23 tons/year for 64 ha (359 kg/ha). The estimation of soybean load was a negative 15 tons/year for 717 ha (−21 kg/ha), which meant that the nitrogen in the yield was greater than the FAR. The results also confirmed the yield absorption ratio in relation to the FAR. The load from the paddy for the entire area was also estimated using the percolation rate and the water quality load underneath the farmland was estimated to be 89 tons/year.     

双季杂交稻“肥促水调”栽培技术的应用

选用优势强、品质优的杂交组合,早季中熟搭配晚季迟熟组合,培育壮秧,控制分蘖肥用量,增大后期施肥量,超前搁田控制苗峰,在一定穗粒基础上,实现总粒数、实粒数和经济系数的大幅度提高,从而提高产量．     

秸秆还田配施氮肥对春玉米氮素利用及土壤氮素平衡的影响

通过8年田间定位试验,研究玉米秸秆还田配施氮肥对春玉米产量、剖面土壤无机氮积累、氮素平衡和氮肥利用效率的影响。结果表明,通过线性加平台回归方程,求得2012~2019年最高玉米产量所需的适宜施氮量依次为202.7、193.7、182.2、171.2、163.6、156.1、150.7和150.5 kg/hm²。氮素表观损失量和土壤残留矿质氮量均随着施氮量增加而显著增加,两者与施氮量之间均呈显著正相关。每增加10 kg/hm²施氮量,土壤残留矿质氮量、氮素表观损失量分别增加9.09~10.34、5.89~7.34 kg/hm²。当施氮量超过150 kg/hm²时,各处理间玉米吸氮量差异不显著,土壤残留矿质氮、氮素表观损失量之间差异均达显著水平（P<0.05）。随着施氮量增加,氮肥利用率呈先增加后减小趋势,当施氮量为150 kg/hm²时,两年氮肥利用率分别达到最高（75.2%和92.3%）。当施氮量为210~330 kg/hm²,剖面土壤无机氮残留量显著增加,造成土壤无机氮在土壤深层（60~100 cm）的大量累积。     

小麦花生两熟制一体化施肥氮效应研究

小麦花生两熟制一体化双高产栽培大田N肥试验表明：前茬（小麦）施N不仅小麦增产显著,而且具有较大的后效作用;后茬（麦套）花生施N花生增产显著,而对前茬小麦籽粒无明显增产作用;在前茬小麦培肥地力的基础上,当茬配施一定数量的N肥,有利于充分发挥花生的增产潜力;小麦花生各6750～7500kg／hm2高产田全年需施N263～356kg／hm2,前后两作适宜的分配比为1：0．4～0．55。     

麦/油-稻轮作下秸秆还田与氮肥管理对直播杂交稻氮素利用特征的影响

【目的】探明秸秆还田和氮肥管理对麦/油后直播杂交稻氮素积累、转运、氮肥利用效率及籽粒产量的影响。【方法】选用优质三系杂交稻宜香优2115，采用二因素裂区设计，麦、油茬田同步开展试验，处理完全一致。主区为麦/油秸秆全量翻埋还田(M1)和秸秆不还田(对照，M0)，副区设4个氮肥管理，即不施氮对照(N0)、m基肥∶m分蘖肥∶m促花肥∶m保花肥比例分别为1∶0∶0∶0(N1)、3∶3∶2∶2(N2)、2∶2∶3∶3(N3)，测定了直播杂交稻主要生育时期各器官的氮素积累量及籽粒产量。【结果】结果表明，两种轮作方式下，氮肥管理对直播杂交稻主要生育时期的氮素积累、齐穗后茎鞘、叶片的氮素转运及稻株氮素利用效率均存在显著或极显著的调控效应。秸秆还田显著提高麦/油茬杂交稻中后期的氮素积累量、茎鞘和叶片的氮素转运量以及氮肥利用效率，其中，氮肥农学利用率、氮肥偏生产力和氮肥表观利用率较秸秆不还田分别提高了34.96%/28.76%、2.52%/2.61%和31.91%/22.30%。同时，油菜秸秆还田下直播杂交稻各生育时期氮素积累和产量较麦秆还田表现更好，籽粒产量提高481 kg/hm2(5.22%)。M1N2处理、M0N3处理下，直播杂交稻各阶段的氮素积累速率明显加大，促进结实期茎鞘和叶片的氮素向穗部转运，成熟期稻株氮素积累量优势明显且有较高的氮素利用效率(麦/油茬稻氮肥农学利用率、偏生产力和表观利用率分别达17.87 kg?kg–1/17.85 kg?kg–1、67.27 kg?kg–1/71.28 kg?kg–1、74.93%/75.05%)，最终实现高产。【结论】在麦/油-稻轮作下秸秆全量还田，配合N2氮肥管理，可有效提高直播杂交稻氮素吸收、利用效率，增加籽粒产量，尤以油菜秸杆还田的效果更好。     

Agronomic and economic evaluation of Sesbania rostrata green manure establishment in irrigated rice

Research on crop establishment methods may improve green manure performance, reduce costs, and increase the adaptability of pre-rice green manure technology in lowland rice-based cropping systems. A two-season field experiment was conducted at the International Rice Research Institute (IRRI) in Los Baños, Philippines in 1991–1992 to compare four establishment practices of Sesbania rostrata green manure (zero tillage, with tillage, relay cropping in rice for 2 or 4 weeks) with four mineral N fertilizer levels (0, 30, 60, and 90 kg urea N/ha) in an intensive irrigated lowland system with three rice crops per year. S. rostrata was grown twice a year during the 43-day dry-wet and wet-dry transition periods between the wet and dry season rice crops.

Grain yield potential and fertilizer responsiveness of rice was generally highest in the dry season. On the other hand, S. rostrata growth was more vigorous in the wet season (long-day period) than in the dry season, regardless of establishment method. Green manure N accumulation was lowest with zero tillage (30 and 90 kg N/ha in dry and wet season, respectively) and highest when it was relay-cropped for two weeks (60 and 180 kg N/ha in dry and wet season, respectively). Land preparation for Sesbania ensured best green manure stand (> 100 plants/m² vs 20–40 plants/m² at no-till establishments) but increased costs of green manuring by US$16/ha compared with other establishment methods. A quadratic response function between mineral fertilizer equivalence and green manure N indicated that up to 75 kg N/ha, lowland rice uses green manure N more efficiently than urea. Depending on season and establishment method, S. rostrata substituted for 35 to 90 kg of split-applied urea N. Benefit-cost ratios indicated that pre-rice green manure use in the wet season under the current fertilizer and labor prices in the Philippines was a less attractive economic option than mineral N fertilizer. This was true for all establishment methods. In the dry season, S. rostrata established by relay cropping gave the highest rate of return. The 2-week relay cropping of green manure with irrigated rice gave highest green manure N accumulation and rice grain yield, and may be economically viable where fertilizer prices are higher or labor costs are lower than in the Philippines.     

氮肥运筹对华北平原限水灌溉冬小麦产量和水氮利用效率的影响

为了解不同氮肥运筹处理对华北平原限水灌溉条件下冬小麦产量、水分和氮素利用效率的影响,在中国农业大学吴桥试验站限水灌溉(播种前灌充足底墒水,春浇拔节水和开花水)条件下,开展了6个不同氮肥运筹处理(157.5 kg N/ha全部做基肥;基肥88.5 kg N/ha 追肥69 kg N/ha;基肥157.5 kg N/ha 追肥69 kg N/ha;基施88.5 kg N/ha 追施138 kg/ha;226.5 kg N/ha全部做基肥;基肥157.5 kg N/ha 追肥138 kg N/ha)的大田试验。结果表明,限水灌溉条件下,不同氮肥运筹处理的冬小麦经济产量和产量构成因素(有效穗数、穗粒数和千粒重)间无显著差异。冬小麦水分利用效率(1.78~1.87 kg/m3)和氮素生理利用效率(39.65~44.42 kg/kgN)随氮肥施用量加大呈下降趋势,而氮肥生产力则随施氮量增加而显著降低。冬小麦氮素转运量及其对籽粒的贡献率(%)均表现为叶片>茎鞘>穗颖。氮肥一次性基施处理的氮素转运量及其对籽粒的贡献率(%)在各氮肥运筹处理中均较高。在华北平原地区,施氮水平在157.5 kg N/ha且一次性基施,是限水灌溉冬小麦高产、高效、简化的适宜施肥方式。     

Effects of straw mulch on mungbean yield in rice fields with strongly compacted soils

In rice-based lowland areas in the Mekong region, the lack of full irrigation water availability for post-rice legume crops and the poor soil physical and chemical conditions are major constraints for development of sound rice/legume double cropping system. In order to improve legume productivity, use of rice straw mulch and various crop establishment methods were examined in two series of mungbean experiments in Cambodia where soils were coarse and strongly compacted. In one set of experiments conducted at four locations in the first year the effect of straw mulch, planting method (manual vs seed drill) and tillage method (conventional vs no-till) was examined. Another set of experiments were conducted in the second year at three locations with four levels of mulch under two planting densities. On average in year 1, mulching of rice straw at 1.5 t/ha increased mungbean crop establishment from 72 to 83%, reduced weed biomass from 164 to 123 kg/ha and increased yield from 228 to 332 kg/ha. Mulch was effective in conserving soil moisture, and even at maturity the mulched area had on average 1% higher soil moisture content. The amount of mulch between 1 and 2 t/ha did not show consistent effects in year 2, partly because some mulch treatments resulted in excessive soil moisture content and were not effective. Rice straw mulch had a significant effect on mungbean yield in 6 out of the 7 experiments conducted in two years, and mean yield increase was 35%. This yield advantage was attributed to better crop establishment, improved growth and reduced weed pressure, but in some cases only one or two of these factors were effective. On the other hand, planting method, tillage method and planting density had only small effects on mungbean yield in most experiments. Only in one location out of four tested, the no-till treatment produced significantly higher yield than the conventional method. Seed drill produced similar mungbean establishment and grain yield to the manual planting suggesting that the planter can be used to save the labour cost which is increasing rapidly in the Mekong region. Maximum root depth varied little with mulch or planting density, and was shallow (<20 cm) in all three locations where this character was determined. It is concluded that while rice straw mulch increased yield of mungbean following rice, the inability of mungbean roots to penetrate the hard pan is a major constraint for development of a sound rice/mungbean cropping system in the lowlands with compacted soils.     

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.     

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.     

Digestion and nitrogen metabolism in beef cattle and in vitro rumen fermentation of autumn grass differing in fertilizer nitrogen application rate

Beef cattle partition dietary nitrogen (N) into meat or excrete it mainly in faeces and urine, which can contribute significantly to water and air pollution. The effects of two inorganic nitrogen (N) fertilizer application rates—15 (LN) or 80 (HN) kg N/ha—to Lolium perenne‐dominant swards in autumn, on herbage chemical composition, intake, digestion and N balance in beef cattle, and in vitro fermentation and methane production were studied. Four growing beef steers used in a 2 × 2 crossover design experiment were offered zero‐grazed grass harvested 21 days post‐N application between July and October. The same grasses were incubated in an eight‐vessel rumen simulation technique in a randomized complete block experiment. Grass dry‐matter (DM) concentration was 26 g/kg lower and crude protein (CP) concentration was 35 g/kg DM higher for HN compared to LN. There was no difference in herbage DM intake or in vivo DM digestibility between treatments. Nitrogen intake and the digestibility of N were higher for HN compared to LN. Total and urine N loss were 41 and 45 g/day greater, respectively, for HN compared to LN, but faecal N loss did not differ between treatments. The quantity of N retained and therefore N‐use efficiency did not differ between LN and HN (25% vs. 22%). In vitro rumen pH and ammonia‐N concentrations were higher for HN compared to LN, whereas volatile fatty acid concentrations and molar proportions did not differ between treatments. In vitro methane and total gas production were 0.9 mmol/day and 280 ml/day lower for HN than LN respectively. Under the particular conditions of this experiment, reducing fertilizer N application rate reduced total and urinary N excretion, which has potential environmental benefits; however, methane output measured in vitro was increased.     

Interactions between non-flooded mulching cultivation and varying nitrogen inputs in rice–wheat rotations

A 3-year field experiment examined the effects of non-flooded mulching cultivation and traditional flooding and four fertilizer N application rates (0, 75, 150 and 225 kg ha⁻¹ for rice and 0, 60,120, and 180 kg N ha⁻¹ for wheat) on grain yield, N uptake, residual soil N_min and the net N balance in a rice–wheat rotation on Chengdu flood plain, southwest China. There were significant grain yield responses to N fertilizer. Nitrogen applications of >150 kg ha⁻¹ for rice and >120 kg ha⁻¹ for wheat gave no increase in crop yield but increased crop N uptake and N balance surplus in both water regimes. Average rice grain yield increased by 14% with plastic film mulching and decreased by 16% with wheat straw mulching at lower N inputs compared with traditional flooding. Rice grain yields under SM were comparable to those under PM and TF at higher N inputs. Plastic film mulching of preceding rice did not affect the yield of succeeding wheat but straw mulching had a residual effect on succeeding wheat. As a result, there was 17–18% higher wheat yield under N0 in SM than those in PM and TF. Combined rice and wheat grain yields under plastic mulching was similar to that of flooding and higher than that of straw mulching across N treatments. Soil mineral N (top 60 cm) after the rice harvest ranged from 50 to 65 kg ha⁻¹ and was unaffected by non-flooded mulching cultivation and N rate. After the wheat harvest, soil N_min ranged from 66 to 88 kg N ha⁻¹ and increased with increasing fertilizer N rate. High N inputs led to a positive N balance (160–621 kg ha⁻¹), but low N inputs resulted in a negative balance (−85 to −360 kg ha⁻¹). Across N treatments, the net N balances of SM were highest among the three cultivations systems, resulting from additional applied wheat straw (79 kg ha⁻¹) as mulching materials. There was not clear trend found in net N balance between PM and TF. Results from this study indicate non-flooded mulching cultivation may be utilized as an alternative option for saving water, using efficiently straw and maintaining or improving crop yield in rice–wheat rotation systems. There is the need to evaluate the long-term environmental risks of non-flooded mulching cultivation and improve system productivity (especially with straw mulching) by integrated resource management.     

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.     

Agronomic performance of late-season rice under different tillage,straw, and nitrogen management

In double rice-cropping system in China, zero tillage in late-season rice with straw return from early season rice is an emerging technology for saving inputs, shortening the lag time between rice crops, avoiding straw burning, and conserving natural resources. The objective of this 2-year field study was to determine the effects of tillage and straw return on N uptake, grain yield, and N use efficiency of late-season rice. Treatments were arranged in a split-plot design with four combinations of tillage and straw return as main plots and three N management practices as subplots. Tillage was either conventional soil puddling or zero tillage with newly harvested crop residue from early season rice either removed or placed on the soil surface without incorporation. The N treatments were zero-N control, site-specific N management (SSNM), and farmers’ N-fertilizer practice (FFP). Straw return regardless of tillage or N management did not reduce rice yield. In the second year, straw return significantly increased grain yield in the zero-N control. Chlorophyll meter readings at heading and total N uptake at maturity were higher with straw return in the zero-N control, suggesting that straw provides nutrients to rice in the late growing period. Zero tillage did not reduce N uptake, grain yield, and N use efficiency compared with conventional tillage. Despite large differences in timing and rate of N application between FFP and SSNM, these two N treatments resulted in comparable N uptake and grain yield of late-season rice regardless of tillage and straw return. These results suggest that zero tillage after early rice with straw return could replace conventional tillage for late rice in the double rice-cropping system in China.     

不同施氮水平对春玉米氮素吸收、转运及产量的影响

采用田间试验研究吉林省中部玉米主产区不同氮水平对玉米产量、氮素吸收、转运及氮肥利用率的影响。结果表明,施用氮肥可以提高干物质最大积累速率和氮素最大吸收速率,并能提前干物质最大积累速率和氮素最大吸收速率出现的天数。在施N 60~180 kg/hm2之间,玉米产量、干物质最大积累速率、氮素最大吸收速率、转运量、转运率及子粒中养分比例等指标均有显著提高;超过N180 kg/hm2,干物质最大积累速率、氮素最大吸收速率、转运量、转运率及子粒中养分比例等指标开始下降。根据玉米产量(y)和施氮量(x)拟合得出,最高产量氮肥用量为184.2 kg/hm2,最佳经济产量氮肥用量为172.9 kg/hm2。氮素农学利用率、氮肥当季回收率及偏生产力随着氮肥用量的提高而显著降低。综合考虑提高玉米产量、效益和氮肥利用效率等方面的要求,在吉林省中部玉米主产区,适宜施氮量为172.9 kg/hm2。     

不同施肥制度对红壤地区双季稻田氨挥发的影响

 为系统地了解不同施肥制度下各生育期氨挥发损失的程度及规律,采用密闭室法对南方红壤地区双季稻田的氨挥发进行了监测。不同施肥制度下氨挥发的变化规律基本相同,施肥后1~3 d内达到峰值,随后逐渐下降,1周后无明显排放。氨挥发速率随施N量增加而增加。早季各处理氨挥发累积量基肥时为1.6~3.6 kg/hm2,分蘖肥时为58~18.2 kg/hm2;而晚季基肥、分蘖肥和穗肥时的氨挥发累积量分别为4.5~7.9、12.3~26.8和1.4~2.4 kg/hm2,早、晚季氨挥发总累积量分别占其施N量的4.5%~15.3%和16.9%~32.8%。相对于不施肥处理,尿素的施用促进氨挥发,而在等氮施用量下,缺P处理通过氨挥发损失的N量较多,较高水平的秸秆和绿肥施用也会增加氨挥发量。此外,氨挥发与田面水NH4+ N浓度及水层pH之间存在正相关关系,气候条件也显著影响氨挥发量。     

Nitrogen and Potassium Fertility Impacts on Aggregate Sheath Spot Disease and Yields of Rice

Abstract

Aggregate sheath spot (AgSS), a disease caused by Rhizoctonia oryzae-sativae, is one of the major rice (Oryza sativa L.) diseases in California. A three year study was initiated in 1998 to evaluate the effect of nitrogen (N) and potassium (K) fertility on the severity of AgSS. A field with a history of AgSS was divided in two: in one the straw was incorporated and in the other the straw was removed. Rice was fertilized annually with five rates of N ranging from 0 to 200 kg ha-¹ (main plot) and six rates of K ranging from 0 to 125 kg ha-¹ (sub-plot). Soil K levels in both fields declined over time and by the third year, soil K was below the critical level of 60 μg K g-¹ soil in both fields. There was a grain yield response to K fertilizer in all 3 years in the field where straw was removed and in the third year when straw was incorporated. Where there was a significant response to K fertilization, yields increased by 560 kg ha-¹. In all fields and years there was a significant yield response to N fertilizer. AgSS severity decreased with increasing N and K fertilizer rates and leaf N and K concentrations at panicle initiation. Furthermore, the leaf N concentration required for maximum rice yields was lower than the leaf N concentration which resulted in the lowest severity of AgSS .     

浙江金华地区水稻土养分供应能力研究

 自1997年早稻开始，在浙江省金华市农业科学研究所试验区稻田设立了监测水稻土生产力及肥力变化的长期肥料定位试验，并在试验区周围10 km范围内选择了21户农民的稻田进行相应的监测试验。试验区内农户间稻田土壤的养分供应能力相差很大，氮供应能力变化于49~116 kg/hm2，磷供应能力变化于13~32 kg/hm2，钾供应能力变化于68~183 kg/hm2。农民常规施肥区的氮肥利用效率很低，氮表观回收率的平均值为14%~26%，氮肥农业效率平均值为4.6~8.2，且农户之间、早晚稻之间均存在较大差异。肥料定位试验结果表明，在连续种植水稻条件下，缺肥区土壤相应的有效养分消耗很快。与NPK全肥区比较，NP区从第2季水稻起，NK区从第3季水稻起，即开始出现减产。针对当地农民现行养分管理的实际情况，就水稻系统发展适地养分综合管理新技术进行了讨论。