Efficient and flexible management of nitrogen for rainfed lowland rice

Nitrogen (N) is the most limiting nutrient in the rainfed lowland rice soils of Laos. Indigenous N supply of these soils was low, ranging from 12 to 64 kg N/ha and was correlated with soil organic matter content. Resource-poor farmers and erratic rainfall are characteristic features of Lao rainfed lowland rice systems. Such climatic and economic factors influence farmers' ability to apply N at the recommended time and therefore efficient and flexible recommendations are required. Research on N management focused on the timing of N applications. Splitting the N recommendation into three equal splits at transplanting, active tillering and panicle initiation increased yields by 12% compared to a single application at transplanting. Agronomic efficiency (AE = kg increase in grain yield/kg N applied) was further increased by 9 kg/kg N if a higher proportion of the N was applied during active tillering and panicle initiation when crop N demand is high. Under conditions of suboptimal N supply, the first N application can be applied from transplanting to 30 d after transplanting without lowering grain yield or AE (for medium duration varieties transplanted 1 month after sowing). The last N application can be made between two weeks before to one week after panicle initiation without lowering yield. These findings provide the basis for an efficient (AE of 20 to 25 kg/kg N) and flexible N management strategy for Lao rainfed lowland rice under conditions of suboptimal N supply.     

Variations in grain nitrogen removal associated with management practices in maize production

Information on N removal by maize (Zea mays L.) grain production is not only required for proper soil N management, but also a prerequisite for environmental risk assessment. The objectives of this field study were to (i) assess the variations of maize grain N removal in relation to weather and agronomic practices, and (ii) determine if a common N removal factor can be used for environment risk assessment with the Ontario N index method. Maize grain samples from four field experiments including treatments of hybrids, rotation systems and fertilizer N levels under different environmental conditions were used to determine nitrogen removal factor (grain N in kg ha⁻¹ divided by grain yield in Mg ha⁻¹, i.e. kg N Mg⁻¹). In general, grain N removal averaged 12.0 kg N Mg⁻¹, which is substantially smaller than 16 kg Mg⁻¹ used in the Ontario N Index model. However, large variations (7.1–16.7 kg N Mg⁻¹) in the N removal factor existed among years, rotation systems, hybrids and level of fertilizer N application. Our data indicate that an index using a constant grain N removal factor may not be representative of different growing conditions, hybrids and fertilizer levels. Hence, care must be taken when using a constant grain N removal factor with the N index approach to assess N overloading for nutrient management legislation purposes.     

Application of manure to no-till soils: phosphorus losses by sub-surface and surface pathways

The acceleration of surface water eutrophication attributed to agricultural runoff has focused attention on manure management in no-till. We evaluated losses of phosphorus (P) in sub-surface and surface flow as a function of dairy manure application to no-till soils in north-central Pennsylvania. Monitoring of a perennial spring over 36 months revealed that dissolved reactive P (DRP) concentrations increased 3- to 28-fold above background levels whenever manure was broadcast to nearby field soils. A study conducted with 30-cm deep intact soil cores indicated that incorporation of manure by tillage lowered P loss in leachate relative to broadcast application, presumably due to the destruction of preferential flow pathways. More P was leached from a sandy loam than a clay loam soil, although differences between soils were not as great as differences between application methods. In contrast, rainfall simulations on 2-m² field runoff plots showed that total P (TP) losses in surface runoff differed significantly by soil but not by application method. Forms of P in surface runoff did change with application method, with DRP accounting for 87 and 24% of TP from broadcast and tilled treatments, respectively. Losses of TP in leachate from manured columns over 7 weeks (0.22–0.38 kg P ha⁻¹) were considerably lower than losses in surface runoff from manured plots subjected to a single simulated rainfall event (0.31–2.07 kg TP ha⁻¹). Results confirm the near-term benefits of incorporating manure by tillage to protect groundwater quality, but suggest that for surface water quality, avoiding soils prone to runoff is more important.

Rational nitrogen fertilization in intensive cropping systems

The objective of a rational N fertilization program is to account for the sources and fate of N while estimating crop N needs. Efficiency of N use will vary with cropping systems and N sources. Management technologies that affect N use efficiency include the amount of N applied, timing and placement of N fertilizer, and use of inhibitors. One of the main problems in making a fertilizer N recommendation is to account for the contribution of N mineralization to plant available N. Most laboratory procedures do not account for the environmental factors that affect N mineralization and only estimate the size of the mineralizable N pool. However, changes in soil moisture and temperature can dramatically affect the amount and rate of release of mineralized N. Field and modeling techniques are two possible techniques to estimate N mineralization. Field techniques can be divided into soil and plant approaches. Soil incubations in the field provide a quantitative approach while soil nitrate tests during the growing season provide a qualitative approach to estimating N mineralization. The plant is the ultimate integrator of N mineralization. Plant N uptake by an unfertilized crop can provide a quantitative approach with certain precautions. This approach may be costly, labor intensive, and site specific. Crop N uptake during the growing season can be estimated by measuring the tissue N content or using a chlorophyll meter. The chlorophyll meter measures the greenness of the plant and has been shown to be positively correlated to plant N status. Modeling may provide another option by including the factors that affect the rate of N mineralization from a known pool. The two most important variables include soil moisture and temperature. Realistic yield expectations and accounting for existing and projected amounts of available N can improve the accuracy of N recommendations.     

Reducing ammonia volatilization in a no-till soil by incorporating urea and pig slurry in shallow bands

Incorporation of broadcast pig slurry and urea into soil is incompatible with no-till production systems and alternative application methods that reduce NH₃-N loss are required. The objective of this study was to assess the impact of incorporating urea and pig slurry in shallow furrows (banding) on NH₃ volatilization. A field study was conducted on a silty loam soil that had been under no-till for 2 years. Ammonia volatilization was measured for 29 days after urea and pig slurry (140 kg N ha⁻¹) were broadcast or incorporated (5 cm) in bands. High urease activity and soil temperatures as well as an absence of rainfall combined to result in large losses of NH₃-N from all treatments. Broadcast urea lost the greatest proportion of applied N (64%) followed by banded urea (31%), broadcast pig slurry (29%) and banded pig slurry (16%). High emissions from broadcast urea were consistent with previous reports of large volatilization losses on no-till soils. Presence of crop residues and associated high urease activity (288 μg NH₄-N g⁻¹ h⁻¹) at the surface of no-till soils were likely important factors contributing to these high emissions. Incorporation of slurry and urea in bands was not as efficient in reducing volatilization as expected but not for the same reason. Relatively high emissions from banded slurry were the result of an incomplete incorporation of slurry in the shallow bands and indicate that the benefit of this practice is limited at high slurry application rates. In banded urea plots, hydrolysis of concentrated urea likely resulted in high localized NH₄ ⁺ concentrations and pH, which increased NH₃ source strength and emissions. Our results therefore suggest that incorporating urea in bands may not be as efficient for reducing NH₃ emissions as incorporation of broadcasted urea which results in lower soil urea concentrations.     

On-farm evaluation of leaf color chart for need-based nitrogen management in irrigated transplanted rice in northwestern India

Nitrogen use efficiency (NUE) in rice is low due to the inefficient management of fertilizer N by farmers. We evaluated a leaf color chart (LCC) as a simple tool for improving the time and rate of N fertilizer use in farmers’ fields for 4 years (2000–2003) in irrigated rice in northwestern India. Application of N fertilizer whenever leaf greenness was less than shade 4 on the LCC (the critical LCC value) produced rice grain yields on a par with blanket recommendation of applying 120 kg N ha⁻¹ in three equal splits in different years, but it resulted in an average saving of 26% fertilizer N across villages and seasons. In most situations, there was no significant advantage of applying 20 kg N ha⁻¹ as basal N at transplanting on grain yield and NUE of rice compared with no basal N. Use efficiencies of fertilizer N were higher when N was applied using LCC with a critical value of 4 than the recommended practice of applying 120 kg N ha⁻¹ in three equal split doses on all sites and in all years. The LCC with a critical value of 4 for real-time N management can be efficiently used to increase NUE in all types of inbred rice cultivars presently popular with the farmers of the Indian Punjab. The LCC is a cheap and easy-to-use tool that allows real-time N management by farmers on a large area leading to improved fertilizer N use efficiency, and reduced risks associated with fertilizer N application.     

Comparative response of bread and durum wheat cultivars to nitrogen fertilizer in a rainfed Mediterranean environment: soil nitrate and N uptake and efficiency

A 3-year multi-site study was carried out on rainfed Vertisols under Mediterranean conditions in southern Europe to determine the influence of the N fertilizer rate on soil nitrates, N uptake and N use efficiency in bread wheat (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. Durum Desf.) in rotation with sunflower (Heliathus annuus L.). Nitrogen fertilizer rates were 0, 100, 150 and 200 kg N ha⁻¹ applied in equal proportions at sowing, tillering and stem elongation. The experiment was designed as a randomized complete block with a split plot arrangement and four replications. Nitrogen harvest index (NHI), N uptake/grain yield (NUp/GY), N use efficiency (NUE), N utilization efficiency (NUtE), N uptake efficiency (NUpE) and N apparent recovery fraction (NRF) were calculated. Differences were observed in N use efficiency between the two modern bread wheat and durum wheat cultivars studied. In comparison to durum, bread wheat displayed greater N accumulation capacity and a more efficient use of N for grain production. While under N-limiting conditions, the behavior was similar for both wheat types. No difference was noted between wheat types with regard to changes in soil residual levels over the study period at the various sites. The 100-kg ha⁻¹ N fertilizer rate kept soil nitrates stable at a moderate level in plots where both wheat types were sown.     

Early nitrogen supply as an alternative management for a cover crop-maize sequence under a no-till system

Nutrient Cycling in Agroecosystems - The use of a controlled-release fertilizer (CRF) was studied in a traditional rainfed olive grove in a Mediterranean climate where precipitation is very...     

On-farm estimation of indigenous nitrogen supply for site-specific nitrogen management in the North China plain

Estimating indigenous nitrogen supply (INS) by measurement of crop N uptake in N omission plots for site-specific N management is not feasible on a routine basis because it involves destructive plant sampling and plant tissue analysis, which is time-consuming and expensive. The objective of this study was to determine the amount of INS and develop a method to estimate it using soil testing in the North China plain (NCP). On-farm experiments at 229 sites were conducted from 2003 to 2005 in seven key winter wheat (Triticum aestivum L.)/summer maize (Zea mays L.) production regions of the NCP. The mean INS during the wheat-growing season was129 kg N ha⁻¹ with a range from 62 to 212 kg N ha⁻¹, and it varied from 69 to 202 kg N ha⁻¹ with a mean of 142 kg N ha⁻¹ during the maize-growing season. Considering all sites, the variability of INS was not simulated by initial soil N _min or apparent N mineralization (N _organic) alone, while together they could explain about 38% and 60% of INS during the wheat and maize-growing seasons, respectively. During the wheat-growing season, mean N _organic was 63 kg N ha⁻¹, and 59% and 33% of its variation could be explained by SOM in high-yielding regions (mean yield, 7.6 t ha⁻¹) and low-yielding regions (mean yield, 5.3 t ha⁻¹), respectively. Mean N _organic during the maize-growing season was 109 kg N ha⁻¹, 22% of which could be explained by SOM across all sites. An average of 40% and 42% of INS variation could be explained by both SOM and initial soil N _min content during the wheat and maize-growing seasons, respectively. We conclude that the accuracy of estimating crop N requirement for site-specific N management will be increased by using initial soil N _min and SOM.     

Use of chlorophyll meter for nitrogen management in lowland rice

The chlorophyll meter (SPAD-502) can be used to diagnose the nitrogen (N) status of rice (Oryza sativa L.) to decide for fertilizer-N side-dressing. The objective of this study was to determine the relationships between SPAD meter readings, unadjusted and adjusted for specific leaf weight (SLW) and N on dry weight basis (Ndw), N on leaf area basis (Na) and yield. The correlation coefficients (r) between SPAD and Ndw ranged from 0.82 to 0.90; between SPAD and yield, from 0.75 to 0.90; and between SPAD/SLW and yield from 0.77 to 0.85 on pooling the data experiment-wise. The corresponding r values over all experiments were 0.87, 0.81 and 0.80, respectively. The results of better relationship between SPAD and Ndw; and between SPAD and yield in the late reproductive and early ripening phases allows prediction of plant N status based on direct SPAD meter readings. It is quick, simple and non-destructive unlike N prediction based on Kjeldahl procedure or SPAD/SLW.     

Minimizing nitrogen losses from a corn–soybean–winter wheat rotation with best management practices

Best management practices are recommended for improving fertilizer and soil N uptake efficiency and reducing N losses to the environment. Few year-round studies quantifying the combined effect of several management practices on environmental N losses have been carried out. This study was designed to assess crop productivity, N uptake from fertilizer and soil sources, and N losses, and to relate these variables to the fate of fertilizer 15N in a corn (Zea mays L.)-soybean (Glycine max L.)-winter wheat (Triticum aestivum L.) rotation managed under Best Management (BM) compared with conventional practices (CONV). The study was conducted from May 2000 to October 2004 at Elora, Ontario, Canada. Cumulative NO₃ leaching loss was reduced by 51% from 133 kg N ha⁻¹ in CONV to 68 kg N ha⁻¹ in BM. About 70% of leaching loss occurred in corn years with fertilizer N directly contributing 11–16% to leaching in CONV and <4% in BM. High soil derived N leaching loss in CONV, which occurred mostly (about 80%) during November to April was attributable to 45–69% higher residual soil derived mineral N left at harvest, and on-going N mineralization during the over-winter period. Fertilizer N uptake efficiency (FNUE) was higher in BM (61% of applied) than in CONV (35% of applied) over corn and wheat years. Unaccounted gaseous losses of fertilizer N were reduced from 27% of applied in CONV to 8% of applied in BM. Yields were similar between BM and CONV (for corn: 2000 and 2003, wheat: 2002, soybean: 2004) or higher in BM (soybean: 2001). Results indicated that the use of judicious N rates in synchrony with plant N demand combined with other BMP (no-tillage, legume cover crops) improved FNUE by corn and wheat, while reducing both fertilizer and soil N losses without sacrificing yields.     

包裹型缓／控释肥对冬小麦产量、土壤无机氮和氮肥利用效率的影响

采用超大区田间试验,以不施氮、传统氯素管理方式和优化氮素管理方式为对照,研究冬小麦施用包裹型缓／控释肥（包裹肥料）对产量、土壤无机氮和氮肥利用效率的影响,并对冬小麦施用包裹型缓／控释肥效果进行评价,结果表明：与传统氮素管理方式相比,优化氮素管理方式和包裹肥料处理在分别节省了78％和67％的氮肥的条件下,获得了和传统氮素管理方式相似的冬小麦子粒产量;采用氮素优化管理模式和施用包裹肥料显著降低了土壤无机氮残留和氮素表观损失,从而显著提高了氮肥利用率;与优化氮素管理方式相比,施用包裹肥料可一次性基施,省时省力,提高了经济效益。     

Aboveground nitrogen in relation to estimated total plant uptake in maize and bean

The main objective of this field study was to estimate the total plant uptake of soil mineral N in maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) grown in crop rotations under different N content in Nicaragua. Secondary objectives were to estimate the fraction of the measured soil mineral N content taken up in this way, and to determine how the measured N in plant aboveground parts was related to the total mineral N uptake. A large variation in N content was obtained by using data from fertilisation experiments. Plant total N uptake was estimated as the residual N in a mass balance calculation of soil mineral N. Mineral N content in the top 0–0.3 m soil layer in the field cultivations and in tubes isolated from root uptake, and N content in aboveground plant parts were measured every 30 days. Estimated plant total uptake of soil mineral N varied considerably (2.5–14 g N m⁻² 30 day⁻¹) over periods and N treatments. The range of variation was similar for maize and bean. The fraction of the soil mineral N that was taken up by the plant daily varied more in maize (about 0.03–0.12 day⁻¹) than in bean (about 0.05–0.08 day⁻¹). Our results suggest that monthly changes in N in aboveground plant parts were linearly related to plant total N uptake during the same period. Aboveground plant N constituted between about 55% and 80% of total uptake of soil mineral N in maize depending on period within season, whereas for bean it was more constant and smaller (about 40%).     

9. Improving nitrogen fertilization in mechanized rice culture

Rice is produced in highly mechanized and energy intensive water-seeded and dry-seeded systems in the United States. Nitrogen fertilization management relative to N source and time of application differs in the two systems because of the timing of soil submergence which influences N retention in the soil. Nitrogen management studies show that N fertilizer efficiency is maximized in water-seeded rice when ammonical N is placed 5 to 10 cm in the soil immediately before flooding. Nitrogen applied on a dry soil surface immediately before flooding dry-seeded rice results in N movement into the soil and retention for plant utilization. Nitrogen application preplant or into water after flooding results in N losses in dry-seeded rice. Split N application gives acceptable N efficiency when 65 to 75% of the total N fertilizer requirement is applied preflood followed by a midseason N topdressing. Sulfur-coated urea and nitrapyrin soil incorporated with urea reduce N loss in dry-seeded rice. Total N requirements of rice in the cultural systems is dependent on cultivar, soil N fertility and other factors. Plant analysis research establishes critical N concentrations in semidwarf and tall rice cultivars in the water-seeded system.     

Transformations and losses of fertilizer nitrogen on no-till and conventional till soils

A field study was conducted in 1982 to measure the effect of no-till (NT) and conventional till (CT) systems on N transformation after surface and subsurface applications of N fertilizers. Urea, urea-ammonium nitrate (UAN) solution, (NH₄)₂SO₄ (AS), and CA(NO₃)₂ were applied to NT and CT plots (5.95 m²) at a rate of 448 kg N ha^–1. A comparison of fertilizer N recovered in soils receiving incorporated or surface applied N was used to estimate NH₃ volatilization while denitrification was estimated from fertilizer N recovered in the presence and absence of nitrapyrin with incorporated N. Immobilization was assessed in microplots (0.37 m²) after surface application of (¹⁵NH₄)₂SO₄ to NT and CT systems at a rate of 220 kg N ha^–1.The results indicate little difference between NT and CT systems on urea hydrolysis rates and immobilization of surface applied fertilizer N. Approximately 50% and 10% of the surface applied N was recovered in the inorganic and organic fractions, respectively, on both tillage systems. The N not recovered was likely lost from plot areas through soil runoff. Incorporation of UAN, urea and AS resulted in 20 to 40% greater inorganic N recovery than from surface application. Nitrification rates were greater under the NT than the CT system. The similarities in concentration in the various N pools observed between the two tillage systems may be partially due to the short length of time that NT was imposed in this field study (<1 year) since other researchers using established tillage systems (>5 y) indicate that NT tends to promote decreased efficiency of fertilizer N.     

长效氮肥一次基施在春玉米上的试验效果

用高分子树脂包膜尿素、改性长效碳铵及普通尿素中加入尿酶抑制剂的氮肥(长效氮肥)与钙镁磷肥、氯化钾混配一次基施,结果表明,施用长效氮肥比普通氮肥增产5.36%~8.33%,植株后期各部位的养分含量水平比普通尿素处理的高,化肥吸收率亦提高1.71%~4.04%。     

Yield response and nitrogen utilization efficiency by drip-irrigated potato

Two field experiments were conducted in the Jordan Valley to evaluate potato response to N fertigation. Nitrogen as ammonium sulphate was supplied through irrigation water (fertigation) at rates of 0, 35, 70 and 105 mg N l^-1. Soil N application treatment equivalent to the fertigation treatment of 70 mg N l^-1 was included. ¹⁵N labelled ammonium sulphate was used to evaluate the N recovery and utilization efficiency. Yield increased by the N rate. The soil N application gave higher yield than the zero N and lower than the fertigated treatments. The increase in yield was due to the increase in the size of the tubers. The specific gravity was the highest with the zero N. The index ratios of potato tubers were similar with all treatments. The N derived from fertilizers by both tubers and shoots, increased with the N rate regardless of the method of application. The soil application treatments had fertilizer utilization as high as the fertigation treatments and produced total tuber yield not significantly different from that obtained by the fertigation treatment with similar rate. This might be attributed to the poor fertilizer distribution in the root zone in the fine textured soil. The low value of the fertilizer utilization of the plant receiving the ¹⁵N in the preceding season suggested possibilities of rapid transformation and immobilization by the soil microorganisms.     

Crop responses to 15N-labelled organic and inorganic nitrogen sources

A major challenge for low-external-input farming systems is to secure the N supply. Lack of synchrony between mineralization of organic N sources and plant N requirements is causing many growers to use different techniques to overcome this problem. One of these techniques is the application of soluble water extracts of different farm residues and plants. A field study was conducted to study the crop uptake of applied ¹⁵N-labeled alfalfa and clover extracts as compared to the N uptake from¹⁵N-glycine and three levels of ¹⁵N-(NH₄)₂SO₄. The results show that total N accumulation in the field crops, squash and lettuce was primarily affected by the amount of added N (P ≤ 0.05) and not by the form in which the N was applied (P ≤ 0.05). The utilization efficiencies of N (pNdff) from plant extracts and glycine increased (P ≤ 0.05) gradually from 10, 20, to 30 days after application in contrast to (NH₄)₂SO₄ which peaked in utilization efficiencies of 56% around 20 days after application. The pNdff reached 60%, 40% and 36% of the applied glycine, alfalfa and clover extracts, respectively in lettuce. Squash showed the same pattern during at 10, 20 and 30 days; however, the proportion of N derived from most of the treatments was higher in squash than in lettuce (P ≤ 0.05). These results indicate that plant extracts of clover and alfalfa can be used as efficient N fertilisers in low-external-input agroecosystems.     

一站服务型节能管理方法探讨

节能管理工作是整个企业管理的重要组成部分,管理节能是实现节能降耗最简单、经济、快速的方法,通过对一站服务型节能管理方法的介绍及典型实例分析,说明一站服务型节能管理方法可以实现双方的双赢互利。     

非包膜型缓释复混肥对辣椒产量与氮素利用率的影响

采用田间试验的方法研究了非包膜(混合)型缓释复混肥在辣椒上的应用效果。结果表明,等量的氮磷钾养分条件下缓释复混肥比普通复混肥有一定的增产和改善品质的效果。其中缓释肥2号的增产效果明显,一次基施的肥效达到常规分次施肥,比普通复混肥一次施用增产13.7%～24.6%。施用缓释复混肥还可提高氮肥利用率,其中缓释肥2号的农学生产率比复混肥一次施用相对增加61.2%～68.8%,比常规分次施肥相对增加4.0%～11.1%;氮素吸收利用率比普通复混肥一次施用处理增加10.29%～10.89%,比常规分次施肥增加3.79%～5.85%。