Management of nitrogen by fertigation of potato in Lebanon

Reports on soil and groundwater contamination with nitrates in Lebanon and other developing countries could be related to the mismanagement of water and fertilizer inputs. The objective of this work was to determine the N requirements and N-use efficiency of a main-crop potato in Lebanon, irrigated by a drip system, compared to the farmer's practice of macro-sprinkler. In the drip irrigation, fertilizers input was as soil application at the time of sowing or added continuously with the irrigation water (fertigation). Nitrogen-fertilizer recovery was determined using ¹⁵N-labeled ammonium sulfate. Fertigation with continuous N feeding based on actual N demands and available sources allowed for 55% N recovery. For a total N uptake of 197 kg ha^–1 per season in the lower N rate, the crop removed 66 kg N ha^–1 from fertilizers. The spring potato crop in this treatment covered 44.8% of its N need from the soil and 21.8% from irrigation water. Higher N input increased not only N derived from fertilizers, but also residual soil N. Buildup of N in the soil with the traditional potato fertilization practice reached 200 kg N ha^–1 per season. With increasing indications of deteriorating groundwater quality, we monitored the nitrate leaching in these two watering regimes using soil solution extractors (tensionics). Nitrate leaching increased significantly with the macro-sprinkler technique. But N remained within the root zone with the drip irrigation. The crop response to applied N requires a revision of the current fertilizer recommendation in semi-arid regions, with an improved management of fertilizer and water inputs using fertigation to enhance N recovery.     

Agronomic and environmental aspects of phosphate fertilizers varying in source and solubility: an update review

This review discusses and summarizes the latest reports regarding the agronomic utilization and potential environmental effects of different types of phosphate (P) fertilizers that vary in solubility. The agronomic effectiveness of P fertilizer can be influenced by the following factors: (1) water and citrate solubility; (2) chemical composition of solid water-soluble P (WSP) fertilizers; (3) fluid and solid forms of WSP fertilizers; and (4) chemical reactions of P fertilizers in soils. Non-conventional P fertilizers are compared with WSP fertilizers in terms of P use efficiency in crop production. Non-conventional P fertilizers include directly applied phosphate rock (PR), partially acidulated PR (PAPR), and compacted mixtures of PR and WSP. The potential impacts of the use of P fertilizers from both conventional (fully acidulated) and non-conventional sources are discussed in terms of (1) contamination of soils and plants with toxic heavy metals, such as cadmium (Cd), and (2) the contribution of P runoff to eutrophication. Best practices of integrated nutrient management should be implemented when applying P fertilizers to different cropping systems. The ideal management system will use appropriate sources, application rates, timing, and placement in consideration of soil properties. The goal of P fertilizer use should be to optimize crop production without causing environmental problems.     

10. Improving nitrogen fertilizer efficiency in lowland rice in tropical Asia

Rice production in Asia must increase 2.2–2.8% annually to keep abreast of increasing population. Greater fertilizer use and crop intensification together with varietal improvement and investment in irrigation will all contribute to increased rice supply. Because fertilizer and input prices have risen faster than the price of rice, increasing fertilizer N efficiency will be a major challenge for rice researchers and farmers. Greater fertilizer N efficiency may be achieved through improved timing and application methods, and particularly through better incorporation of basal fertilizer N without standing water. Other promising alternative practices are use of N-efficient rice varieties, hand or machine deep placement of urea supergranules, and use of slow release N fertilizers. Research challenges include development of placement machines for prilled urea and identification of cost-efficient nitrification and urease inhibitors. Under the present resource-scarce situation in many tropical Asian countries, several complementary practices must be followed to supplement inorganic N sources. Fertilizer supplies and proper price support should be maintained and wherever possible increased, and appropriate fertilizer materials and application methods must be devised to increase N use efficiency in lowland rice, so that increasing rice requirements are fulfilled.     

Field evaluation of agronomic effectiveness of multi-nutrient fertilizer briquettes for upland crop production

Low nutrient recovery in upland crop production systems has prompted studies to improve the current nutrient management practices to increase fertilizer efficiency. Field studies were conducted in two growing seasons (2012 and 2013) under two land management systems (till and no-till) to evaluate agronomic effectiveness of a multi-nutrient fertilizer briquette (fertilizer briquettes) for upland crop production, using corn as test crop. The fertilizer briquettes were produced through a simple physical compaction of ordinary granular fertilizers with a final nutrient composition of 23.9% N, 19.2% P₂O₅, 19.1% K₂O, 0.9% Zn, and 2.5% S. The agronomic efficiency of the fertilizer briquettes were compared with commercial N sources, urea and ammonium sulfate supplied separately with phosphorus (P), potassium (K), zinc (Zn), and sulfur (S; for urea alone). During the wetter (2013) weather conditions, the fertilizer briquette treatment consistently produced the highest yields in both locations. At Ames Plantation, the fertilizer briquette treatment increased grain yields by ~ 16 and ~ 23% over the treatments having ammonium sulfate and urea granular fertilizers, respectively, and, in Jackson, by 16 and 34% respectively. Nutrient recovery efficiency was also greatest with the fertilizer briquettes treatment. However, during the drier weather conditions (2012), the fertilizer briquettes treatment was the least effective among the three treatments in terms of biomass and grain yields, and nutrient recovery efficiency. We conclude, with adequate rainfall conditions, the fertilizer briquettes could be an efficient fertilizer for upland crop production. However, under drier weather conditions where soil moisture is limited, the fertilizer briquettes may not be an ideal fertilizer source for upland crop production.     

Field-scale analysis of water and nutrient use efficiency for vegetable production in a West African urban agricultural system

Urban agriculture increasingly supplies food and non-food services to the rapidly growing West African cities. However, with its typically heavy use of fertilizers and uncontrolled use of water, it bears severe risks of soil and groundwater pollution. This study was carried out in Bobo Dioulasso (Burkina Faso, West Africa) at two commercial gardening sites. It aimed at performing a detailed characterization of farmer’s water and nutrient management strategies. Four vegetable crops were monitored (tomato, cabbage, carrot and lettuce). Water inputs (rainfall and irrigation), nutrient inputs (organic and mineral fertilizers and nutrients in irrigation water) and crop uptake were monitored over a 1–2-year period. In addition, pan lysimeters allowed monitoring drainage. Depending on the site, 3–8% of the input water was lost by drainage, i.e., as much as 293 mm/year at one of the sites. During the dry season, when the farmer has full control over the water supply, water application exceeded plant requirements by as much as 40%, which reveals inefficient water use. Up to 800 kg N ha⁻¹, 140 kg P ha⁻¹ and 500 kg K ha⁻¹ were applied for a single crop cycle. With few exceptions, crops tended to be strongly over-fertilized, except for K at one of the two sites. Nutrient supply exceeded crop requirements by 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K per year. These results, in combination with the large observed rates of drainage, are indicative of a high risk of nutrient leaching and groundwater contamination. The partial factor productivity of nutrients tended to be low. These results therefore suggested that there is scope to substantially reduce nutrient application rates in these systems without adverse effects on yields, which would be beneficial for groundwater resources and improve the economic returns.     

Irrigation and nitrogen managements affect nitrogen leaching and root yield of sugar beet

Irrigation water and nitrogen (N) are the limiting factors for crop production in arid and semi-arid areas. However, excess irrigation and N application rate is a source of groundwater contamination. Partial root drying irrigation (PRD) is the water-saving technique and would perform as a controlling measure of groundwater N contamination as it reduces irrigation amount. Sugar beet is an industrial crop that is widely grown in arid and semi-arid area where N and water are highly required for high sugar beet yield production. The objectives of this study were to evaluate the interaction effect of ordinary furrow irrigation (OFI), and PRD irrigation as variable alternate furrow irrigation (VAFI) and fixed alternate furrow irrigation (FAFI) with different N application rates (0, 80, 160, and 240 kg ha^?1) on sugar beet root and sugar yield, yield quality, drainage water, N leaching, N uptake, and N efficiency indices. Results indicated that the alternate furrow irrigation (AFI) used 24% less irrigation water compared with the OFI in the study region, whereas its sugar yield was reduced just by 9%. However, it resulted in higher water productivity by 12 and 17% for root and sugar yields, respectively. In different N application rates nitrate leaching reduced by 46 and 52% in the VAFI and FAFI irrigation treatments compared with the OFI, respectively. Physiologic nitrogen efficiency enhanced in VAFI with 160 kg N ha^?1 that implied higher production of uptake N in plants. Therefore, considering the nitrogen use economics and environmental impacts, the VAFI and 160 kg N ha^?1 were preferred to the other irrigation treatments and N application rates in the study region. Higher nitrogen saving occurred because of less leaching and higher soil residual in the AFI treatment compared with the OFI. Furthermore, leaf level stress sensitivity index indicated that VAFI increased the sugar beet resistance to water stress. Overall, in order to avoid N losses in sugar beet production, the amount of N fertilizer should be reduced in proportion to the amount of soil water available under VAFI water-saving irrigation.     

Higher and better yields with less environmental pollution in Egypt through balanced fertilizer use

Nitrogen use per unit area in Egyptian agriculture is over 300 kg ha^–1. An annual average increase of about 2% till year 2000 was estimated. Fertilizers use is characterised by excessive N application, moderate P use and neglection of K and micronutrients. Consequently, nutrient imbalance occurs in crop plants. Subsidising N fertilizers resulted in their misuse and increasing losses. Efficiency of N use in different areas and crops is low. High nitrate concentrations were detected in drainage as well as ground water. Subsidy was removed and fertilizers handling was left to the free market in 1992/93, which resulted in drastic price increases. It could be demonstrated for many years and in farmers fields that yields can be considerably increased (20%) through balanced fertilizers use based on soil testing and plant analysis and adjusted according to the prevailing farming system, leading to more return and less N-use. Use of micronutrients foliar fertilizers leads to increase in root growth and higher uptake of macronutrients. Use of relatively high rates of fertilizers is still a must, however it should be optimised to obtain the highest possible efficiency. Making crop and location specific fertilizer recommendations available to farmers helps in increasing high quality yields, which results in high economic benefits, keeping agricultural production sustainable and decreasing pollution.     

Need based nitrogen management using the chlorophyll meter and leaf colour chart in rice and wheat in South Asia: a review

Fertilizer nitrogen (N) is one of the major inputs in rice–wheat production systems in South Asia. As fertilizer N has generally been managed following blanket recommendations consisting of two or three split applications of preset rates of the total amount of N, improvement in N use efficiency could not be achieved beyond a limit. Feeding crop N needs is the most appropriate fertilizer N management strategy to further improve N use efficiency. Since plant growth reflects the total N supply from all sources, plant N status at any given time should be a better indicator of the N availability. The chlorophyll meter and leaf colour chart have emerged as diagnostic tools which can indirectly estimate crop N status of the growing crops and help define time and quantity of in-season fertilizer N top dressings in rice and wheat. Supplemental fertilizer N applications are thus synchronized with the N needs of crop. The chlorophyll meter may not be owned by South Asian farmers individually, but it can be made available to farmers through village cooperatives, extension specialists, and crop consultants. Leaf colour chart, a simple and cost-effective device has already penetrated into South Asian farming and increasing numbers of farmers are finding it helpful in efficiently managing N fertilizers. This paper reviews the results of investigations carried out using these diagnostic tools in managing need based N applications in rice and wheat in South Asia.     

腐植酸灌溉肥对温室黄瓜质量及土壤理化性状影响的研究

试验表明，腐植酸灌溉肥和常规化肥处理黄瓜产量分别比对照增加29．72％和22．91％，两个处理之间差异不明显；不同肥处理对黄瓜生物性状影响明显，两个处理间腐植酸灌溉肥略好于常规施肥；不同处理提高了黄瓜中Vc、水溶性糖含量，改善黄瓜品质，腐植酸灌溉肥处理明显好于常规化肥；不同处理均增加了土壤中有机质、碱解氮、速效磷、速效钾含量，为作物生长发育提供了更丰富营养物质，两个处理之间差异不明显。对土壤物理性质影响腐植酸灌溉肥处理明显好于常规化肥。     

An LSTM-based mixed-integer model predictive control for irrigation scheduling

The development of well-devised irrigation scheduling methods is desirable from the perspectives of plant quality and water conservation. Accordingly, in this article, a mixed-integer model predictive control system is proposed to address the daily irrigation scheduling problem. In this framework, a long short-term memory (LSTM) model of the soil–crop–atmosphere system is employed to evaluate the objective of ensuring optimal water uptake in crops while minimizing total water consumption and irrigation costs. To enhance the computational efficiency of the proposed method, a heuristic method involving the logistic sigmoid function is used to approximate the binary variable that arises in the mixed-integer formulation. Through computer simulations, the proposed scheduler is applied to homogeneous and spatially variable fields. The results of these simulation experiments reveal that the proposed method can prescribe optimal/near-optimal irrigation schedules that are typical of irrigation practice within practical computational budgets.     

缓/控释肥料的新进展及特性评价

缓／控释肥料具有提高肥料利用率、降低环境污染、提高作物产量等特点,因而成为目前肥料研究与开发的热点。本文综述了各种类型缓／控释肥料的最新研究进展,介绍了几种检测缓／控释肥养分释放特性的方法。此外,文章分析了缓／控释肥料推广应用中存在的问题,并对其未来发展进行了展望。     

Principles of fertilizer use for trickle irrigated crops

Under trickle irrigation only a portion of the soil volume around each plant is usually wetted. Typically this is an eliptically shaped volume directly below the emitter. Crop root growth is essentially restricted to this volume of soil and nutrient reserves within that volume can become depleted by crop uptake and/or leaching below the root zone.If nutrients are applied outside the wetted soil volume they are generally not available for crop use. Fertilizer placement is therefore an important consideration for trickle irrigated crops. Thus, applications banded close to the emitters are preferable to broadcast applications. In general, injection of nutrients into the irrigation water (fertigation) gives a better crop response than either banded or broadcast applications. Fertigation gives a flexibility of fertilization which enables the specific nutritional requirements of the crop to be met at different stages of its growth. In comparison with conventional methods of irrigation and fertilization it appears that trickle fertigation can, under some conditions, produce comparable or higher crop yields with substantial savings (of up to 50 percent) in fertilizer useage.Fertilizer materials used for fertigation must be completely soluble in water and must not react with substances in the irrigation water to form insoluble precipitates. An uneven distribution of nutrients within the crop rooting zone occurs under fertigation since immobile nutrients such as phosphate become concentrated around the emitter while mobile ions such as nitrate and potassium move downward and outward with the wetting front and accumulate at the periphery of the wetted soil volume. Plants, however, appear to have the ability to adapt to spatial variability of available nutrients in soils.     

NPK-fertilizer efficiency — a situation analysis for the tropics

This paper examines the efficiency of applied N, P, and K fertilizers under tropical conditions. To meet their food demands, tropical countries are importing large quantities of fertilizers at an enormous cost. There is a need for improving crop yields at a reduced cost and a better understanding of the factors that contribute to the overall efficiency of applied fertilizers. It is estimated that under tropical condition, the efficiency of applied N is less than 50%, less than 10% for P and for K it is somewhere around 40%. Losses of N are mainly due to leaching, runoff and volatile losses of ammonia. Under flooding and in alternate wetting and drying conditions of rice lands and low lands, dentrification and volatile ammonia losses are considerable. The N losses from these soil could be minimized by proper management such as rate, methods and time of application. The coating of urea with S has shown some improvement in increasing efficiency. Nitrification and urea hydrolysis inhibitors can improve fertilizer efficiency in certain situations provided they are properly used. The efficiencies of these inhibitors depend on the nature of the chemical compounds, soil properties, and method of application. Low efficiency of applied P fertilizer is mainly due to retention of P by soil clay fractions and iron and aluminum hydroxides. Even though retained P is not available to the first crop, it is made available to a certain extent to the succeeding crops. The rate and methods of P applications and forms of P determine the efficiency of applied P fertilizers. The use of native rock phosphate along with P fertilizers on acid soils appears to be an attractive alternative in reducing the fertilizer cost. The loss of K in tropical soils is largely attributed to leaching and runoff. To reduce K loss by leaching, it is more advisible to apply K in split doses than a single dose. Liming has a beneficial effect in retention of K and reducing P fixation in acid soils.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank program at National Corn and Sorghum Research Center, Sete Lagos, MG, Brazil.     

Response of dryland wheat to supplemental irrigation and rate and method of N application

A field experiment was conducted on dryland wheat (Triticum aestivum L.cv PBW 175) for four years on a sandy loam soil to evaluate the effect of supplemental irrigation in combination with rate and method of fertilizer N application. The experiment was a split-split plot design consisting of three irrigation treatments (rainfed, one preseeding irrigation and one preseeding + one postseeding irrigation) in the main plot: four fertilizer N rates (0, 40, 80 and 120 kg ha^–1) in the sub-plot and two methods of N application (drilled at the time of seeding and broadcast before preseeding irrigation) in the sub-sub plots. The crop response to supplementary irrigation(s) depended on the growing season water deficits. Broadcasting fertilizer N before preseeding irrigation resulted in the transporting of 39 per cent of the applied N to the sub-soil (20-60 cm depth). This resulted in better crop performance, particularly under low water supplies. A step wise regression was developed that showed water supplies beyond 26 cm of available water plus irrigation/rainfall from seeding to 45 days after were not productive and its distribution between pre- and post-fertilizer application periods affected water and applied N efficiencies. For higher crop yields under low water supply the fertilizer N broadcast before preseeding irrigation is suggested.     

Efficiency, economics, and environmental implications of phosphorus resource use and the fertilizer industry in China

Phosphorus (P) is an essential nutrient for crop production and is often in short supply. The necessary P fertilizers are derived from deposits in the lithosphere, which are limited in size and nonrenewable. China is one of the world’s largest consumers and producers of P fertilizers. Thus, P resource use efficiency in China has an important impact on the worldwide efficiency of P resource use. This study examined the P fertilizer industry in China in terms of P resource use efficiency, economics, and environmental risk, and explored options for improvement through scenario analysis. P resource use efficiency decreased from a mean of 71% before 1995 to 39% in 2003, i.e., from every 10 kg P in rock material, only 3.9 kg P was used to produce fertilizer, 5.6 kg of the residues were discarded at the mining site, and 0.5 kg was manufacturing waste. The decreased efficiency was caused by increased P rock mining activities, especially from small, inefficient miners. Enhanced mining was supported by local governments and by the growing P fertilizer industry, where high-analysis P fertilizers have fourfold higher gross margins than traditional low-analysis fertilizers. Although the growing fertilizer industry is contributing significantly to the development of some regions, the economic efficiency is still lower than in other countries, e.g., in the USA. The P resource is depleting quickly, and the environmental consequences of inefficient use are serious. The amount of accumulated phosphor gypsum was estimated to be 110 Tg, the amount of deteriorated land reached 475 km², and the consumption of ground water was 1.8 billion m³ per year. The low efficiency and serious environmental risk could be attributed to the numerous small inefficient miners, which were supported by intervention of governmental subsidies and taxes after 1995. This study proved that there is a great deal of room for improvement in the resource use efficiency up to 77% by integrated measures, which need broad cooperation of miners, fertilizer plants, and agriculture.     

Efficient fertilizer use for increased crop production: The sub-humid Nigeria experience

The results of five years of collaborative field trials at Samaru, Nigeria on nitrogen, phosphorus, sulphur and potassium fertilizers showed that all these nutrients are needed in the soils.While confirming the widespread deficiencies of N and P, the trials also showed that only moderate amounts of N and P are required to overcome these deficiencies and satisfy crop needs. Nitrogen fertilizers applied at rates of 80 kg/ha should be split applied for a more efficient utilization of the N. Partial acidulation of Togo phosphate rock at 50% produced a product which was agronomically as effective as commercial superphosphate. Preliminary results from nutrient interaction experiments suggest that efficiency of fertilizers can be improved by ensuring appropriate balance of nutrients applied to the soil.     

Agronomic and economic evaluation of Tilemsi phosphate rock in different agroecological zones of Mali

Phosphorus deficiency is known as one of the major constraints to crop production in West Africa. Farmer-managed trials were conducted in three agroecological zones of Mali to evaluate the profitability of Tilemsi phosphate rock (TPR) in different crop-rotation systems in comparison with conventional water-soluble fertilizers. Marginal analyses were used to compare treatments tested. Results show that crop yields using TPR are comparable to those of recommended cotton- or cereal-complex imported fertilizers. The economic evaluation also clearly indicated that direct application of TPR is relatively profitable in comparison with recommended imported fertilizers and that good management enhances the profitability of fertilizers in general. This revised version was published online in August 2006 with corrections to the Cover Date.     

Outlook on fertilizer use efficiency in the tropics

In this paper efficiency of applied fertilizers under tropical conditions is examined. Understanding of the fertilizer efficiency is particularly important for the developing countries mainly because there is need for enhancement of crop yields at a reduced cost. Many of the soil, plant and climatic factors of the tropical regions that contribute to the efficiency of the applied fertilizers have been discussed. Many of the tropical soils are acidic in nature and in these soils efficiency of applied fertilizer is relatively poor, mainly because plant roots are unable to grow and function to their fullest extent in utilizing the soils available nutrients. To enhance yield potentials there is need for understanding of interaction between crop species and soil and climatic variables. Incorporation and adoptation of a suitable application time can greatly enhance efficiency of urea form of nitrogen. Research findings in tropical soils have shown that an initial broadcast application of P and subsequent band treatment is more effective than either method of application alone. Current crop yields in tropical countries are far below the known yield potentials. Such low production potentials are attributed to the lack of suitable crop germplasms and understanding of improved agronomic practices. Intensification of research activities in fertilizer use efficiency in tropical countries is suggested.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank Program in Brazil.     

Can the Synchrony of Nitrogen Supply and Crop Demand be Improved in Legume and Fertilizer-based Agroecosystems? A Review

Asynchrony between nitrogen (N) supply and crop demand is the source of many environmental hazards associated with excess N in the biosphere. In this review, we explore some of the complexity of the synchrony issue in agroecosystems that obtain N via legume rotations or synthetic fertilizers. Studies that have simultaneously compared the fate of both sources of N suggest that in rainfed agricultures, crops recover more N from fertilizer, but a higher proportion of the legume N is retained in the soil and N losses tend not to differ greatly from either source. However, investigations from irrigated cropping systems indicate that legume N is generally less susceptible to loss processes than fertilizers. Such general conclusions need to be qualified by acknowledging that not all comparative studies have used ȁ8best management practices’ when applying the fertilizer or legume residues. When information-intensive management approaches are used, fertilizer-based systems can potentially out-perform the synchrony achieved by legume-based rotations. We suggest that the inclusion of perennials in cropping systems may hold the greatest promise for decreasing the risk of N losses in future farming systems.     

缓释/控释肥料用包膜材料的现状及发展探讨

缓释／控释包膜肥料具有提高肥料利用率、降低环境污染、提高作物产量等特点,因而成为目前肥料研究与开发的热点之一,包膜材料则是影响肥料释放速率的关键。本文简要介绍缓释／控释包膜肥料的研究现状、讨论了若干目前已被采用包膜材料的特点、并对包膜材料的发展前景进行了初步探讨。