Key variable for simulating critical nitrogen dilution curve of wheat: Leaf area ratio-driven approach

Nitrogen (N) dilution curves, a pivotal tool for N nutrition diagnosis, have been developed using different winter wheat (Triticum aestivum L.) tissues. However, few studies have attempted to establish critical nitrogen (N_c) dilution curves based on the leaf area ratio (LAR) to improve the monitoring accuracy of N status. In this study, three field experiments using eight N treatments and four wheat varieties were conducted in Jiangsu Province of China from 2013 to 2016. The empirical relationship of LAR with shoot biomass (expressed as dry matter) was developed under different N conditions. The results showed that LAR was a reliable index, which reduced the effects of wheat varieties and years compared with the traditional indicators. The N nutrition index (NNI) based on the LAR approach (NNI-LAR) produced equivalent results to that based on shoot biomass. Moreover, the NNI-LAR better predicted accumulated N deficit and best estimated the relative yield compared with the other two indicator-based NNI models. Therefore, the LAR-based approach improved the prediction accuracy of N_c, accumulated N deficit, and relative yield, and it would be an optimal choice to conveniently diagnose the N status of winter wheat under field conditions.     

平水年和欠水年渭北旱地冬小麦临界氮浓度稀释曲线构建

降雨波动大和过量施氮是限制渭北旱地冬小麦生产中氮肥高效利用和高产稳产的主要因子。该研究旨在构建2种降雨年型下冬小麦临界氮浓度稀释曲线,分析氮营养指数诊断冬小麦氮素营养状况的可行性,为考虑降雨条件下旱地冬小麦精准施氮提供理论依据。于2017—2021年在陕西合阳县开展4 a定位施氮试验,以晋麦47为试验材料,设置0、60、120、180、240 kg/hm² 5个施氮水平,其中2017—2018年和2020—2021年为平水年,2018—2019和2019—2020年为欠水年。研究2种降雨年型下施氮量对冬小麦氮素利用、产量及产量构成因素的影响,基于2种降雨年型下地上部生物量与植株氮浓度之间的关系,构建临界氮浓度稀释曲线模型和氮营养指数(nitrogen nutrition index,NNI)优化施肥方案。结果表明:1)施氮量、降雨年型及其二者互作效应对穗数、千粒质量、产量影响显著或极显著。2)2种降雨年型下冬小麦临界植株氮浓度和地上部生物量均符合幂函数关系,但模型参数之间存在差异(模型参数a在平水年和欠水年分别为3.33、2.79 g/kg,参数b在平水年和欠水年...     

A New Critical Nitrogen Dilution Curve for Rice Nitrogen Status Diagnosis in Northeast China

In-season diagnosis of crop nitrogen(N) status is crucial for precision N management. Critical N(N_c) dilution curve and N nutrition index(NNI) have been proposed as effective methods to diagnose N status of different crops. The N_c dilution curves have been developed for indica rice in the tropical and temperate zones and japonica rice in the subtropical-temperate zone, but they have not been evaluated for short-season japonica rice in Northeast China. The objectives of this study were to evaluate the previously developed N_c dilution curves for rice in Northeast China and to develop a more suitable N_c dilution curve in this region. A total of17 N rate experiments were conducted in Sanjiang Plain, Heilongjiang Province in Northeast China from 2008 to 2013. The results indicated that none of the two previously developed N_c dilution curves was suitable to diagnose N status of the short-season japonica rice in Northeast China. A new N_c dilution curve was developed and can be described by the equation N_c = 27.7 W~(-0.34) if W ≥ 1 Mg dry matter(DM) ha~(-1) or N_c = 27.7 g kg~(-1) DM if W 1 Mg DM ha~(-1), where W is the aboveground biomass. This new curve was lower than the previous curves. It was validated using a separate dataset, and it could discriminate non-N-limiting and N-limiting nutritional conditions. Additional studies are needed to further evaluate it for diagnosing N status of different rice cultivars in Northeast China and develop efficient non-destructive methods to estimate NNI for practical applications.     

Critical nitrogen content and nitrogen nutrition index for sweetpotato crop

Abstract

Sweetpotato is an important tuber crop for the food security in Island countries of the South Pacific. The allometric relationship between tissue nitrogen (N) concentration and aerial dry matter is unknown. We determined critical N (N_c) content from vegetative stage to harvesting, and estimated the range of variation in N nutrition index (NNI) from two field experiments with varied rates of N (0, 25, 60, 125 and 180?kg N ha^?1 in 2015 and 0, 50, 125, 175 and 250?kg N ha^?1 in 2017). A unified critical N curve (N_c = 3.338?W^?0.307) where W?=?aerial dry matter with W?≥?1.38 t ha^?1, was constructed based on the N concentration in the aerial dry matter. The calculated NNI ranged from 0.69 to 1.23 in 2015 and 0.54 to 1.17 in 2017. The preliminary N_c dilution curve and NNI determined could potentially be used as a parameter for N management.     

Determination of a critical dilution curve for nitrogen concentration in cotton

Several nitrogen (N)‐rate field experiments were carried out in cotton to define dilution curves for critical N concentrations in individual plants (i.e., the minimum N concentration required for maximum growth at any growth stage). Nitrogen application rate had a significant effect on aboveground dry matter, N accumulation, and N concentration. As expected, shoot N concentration in plants decreased during the growing period. These results support the concept of critical N concentration in shoot biomass of single plants as described by Lemaire et al. (2007) and reveal that a dilution curve for critical N concentrations in cotton plants can be described by a power equation. The pattern of critical–N concentration dilution curves was consistent across the two sites. Nitrogen concentration for a given biomass varied greatly with the supply of N. After initial flowering, the N‐nutrition index (NNI) for aboveground biomass of individual plants increased with increasing N rates. Relationships between plant total N uptake and accumulated dry matter in the aboveground biomass can be described by the allometric‐relation equations for each dose of N. Nitrogen‐dilution curves can be used as a tool for diagnosing the status of N in cotton from initial flowering to boll opening. The relationship can also be used in the parameterization and validation of growth models for predicting the N response and/or N requirement of cotton.     

CRITICAL NITROGEN CURVE AND NITROGEN NUTRITION INDEX FOR SPRING MAIZE IN NORTH-EAST CHINA

The study was conducted at three sites during 2008 and 2009 in the North-East China Plain (NECP). Field experiments consisted of five or six nitrogen (N) fertilization rates (0–350 kg N ha^?1). Shoot biomass and N concentration (N_c) of spring maize (Zea mays L.) were determined on six sampling dates during the growing season. Nitrogen application rate had a significant effect on aerial biomass accumulation and Nc. As expected, shoot Nc declined during the growing period. A critical N dilution curve (N_c = 36.5 W ^?0.48) was determined in China, which was a little different from those reported for maize in France and Germany. Besides, the N nutrition index (NNI) calculated from this critical N dilution curve was significantly related to relative grain yield, which can be expressed by a linear with plateau model (R² = 0.66; P < 0.001). NNI can be used as a reliable indicator of the level of N deficiency during the growing season of maize.     

基于叶面积指数构建滴灌玉米营养生长期临界氮稀释曲线

明确宁夏引黄灌区基于叶面积指数(leaf area index,LAI)的滴灌玉米临界氮稀释曲线模型及其适用性,探讨以氮营养指数(nitrogen nutrition index,NNI)为监测指标对滴灌水肥一体化模式下玉米氮素营养状况诊断的可行性。该研究于2017-2018年开展了不同施氮量(0~450 kg/hm^2)下4个田块的试验,采用系统分析和统计建模的方法,分析了LAI和植株氮浓度(plant nitrogen concentration,PNC)的定量关系,构建和验证基于LAI的临界氮稀释曲线模型,并建立理论框架,将基于LAI的临界氮曲线与基于植株干物质(plant dry matter,PDM)的临界氮浓度曲线关联,比较基于LAI和PDM的临界氮曲线之间的差异。结果表明,玉米营养生长期临界氮和LAI符合幂函数关系,拟合模型的评价指标均方根误差(root mean square error,RMSE)和标准化均方根误差(normalized RMSE,n-RMSE)的结果分别为0.09和4.13%,模型具有较好的稳定性。在试验氮素水平范围内,不同生育时期NNI随施氮量的增加而增加,变化范围为0.53~1.34,NNI可以准确地反映滴灌玉米氮素营养状况。在非限氮处理下,玉米植株氮素吸收与LAI成正比,LAI与PDM的异速生长参数接近理论值2/3。构建的基于LAI的临界氮曲线可以有效地识别玉米拔节期至吐丝期植株所需的氮状态,为宁夏滴灌玉米氮肥精确管理提供了一种新的评价方法。     

滴灌番茄临界氮浓度、氮素吸收和氮营养指数模拟

作物的氮浓度随生物量的增加而下降,临界氮浓度是指在一定的生长时期内获得最大生物量时的最小氮浓度值。该文在滴灌条件下,基于3a不同的氮素水平试验,构建了加工番茄地上部生物量的临界氮浓度稀释曲线模型。结果表明,临界氮浓度与地上部最大生物量之间符合幂指数关系,相关系数为R~2=0.947,加工番茄最高(%Nmax)、最低(%Nmin)临界氮浓度稀释模型亦符合幂指数关系,相关系数分别为R~2=0.959、R~2=0.925。基于临界氮浓度建立了加工番茄氮素吸收模型(Nupt)、氮素营养指数模型(NNI),可作为加工番茄氮素营养状况的判别指标,氮素吸收和氮营养指数模型对新疆北疆加工番茄种植区的适宜施氮量诊断结果一致,均以300kg/hm2为最佳施氮量。该研究所建立的临界氮浓度稀释曲线模型较前人建立的模型更具机理性,因此,该模型所得出的分析结果是合适和可靠的,并且可用于指导加工番茄动态精准施肥及为氮素优化管理的建立提供参考。     

基于叶片SPAD估算不同水氮处理下温室番茄氮营养指数

为了探讨临界氮稀释曲线模型在西北地区温室番茄不同水分处理下的适用性以及采用SPAD仪快速准确诊断氮营养状况,该研究以"丽娜"番茄为材料,2013-2015年在陕西省杨凌区温室内进行水分和氮素处理试验,水分处理设置4个水平,分别为全生育期充分灌水处理、仅苗期亏水50%、苗期开花期连续亏水50%和全生育期亏水50%;氮素处理设置3个水平,施氮量分别为0、150和300 kg/hm2,通过2013-2015年试验数据对临界氮浓度稀释曲线模型进行率定和验证,并将该模型参数与番茄全生育期平均日耗水量建立相关关系,提高了临界氮浓度稀释模型在不同水分条件下的适用性。结果表明通过番茄全生育期平均日耗水量和临界氮浓度稀释曲线模型估算得到的临界氮浓度估算值和实际计算值有较好的一致性,其绝对误差为0.13~0.34 g/(100 g),标准误差为0.14~0.39 g/(100 g),决定系数为0.94~0.99,因此采用该方法可以对西北地区温室番茄不同水分处理下临界氮浓度稀释进行准确估算。通过2013-2015年试验数据分析番茄不同叶位叶片SPAD值和氮营养指数(nitrogen nutrition index,NNI)之间相关性,结果表明番茄中位叶片SPAD值与氮营养指数(NNI)有良好的线性相关性(决定系数为0.77~0.98),且该相关系数值与番茄日耗水量呈极显著相关关系,因此通过番茄日耗水量可以估算出NNI与中位叶片SPAD值之间的线性关系,估算出NNI=1时的中位叶片SPAD值,并以此SPAD值进行氮营养诊断。该研究可为西北地区温室番茄实时氮营养诊断和优化氮素管理提供了较好的理论参考。     

Using a nitrogen mineralization index will improve soil productivity rating by artificial neural networks

ABSTRACT

In the Pampas, nitrogen fertilization rates are low and soil organic matter impacts crop yield. Wheat (Triticum aestivum L.) yield was related to total soil nitrogen (total N) and to nitrogen mineralization potential (mineralized N) to determine whether the effects of organic matter may be attributed to its capacity to act as a nitrogen source or to the improvement of the soil physical condition. Data of 386 sites from throughout the region comprised in a recent soil survey were used, in which climate and soil properties to 1 m depth were determined. Artificial neural networks were applied for total N and mineralized N estimation using climate and soil variables as inputs (R² = 0.59–0.70). The models allowed estimating total N and mineralizable N at county scale and related them to statistical yield information. Neural networks were also used for yield prediction. The best productivity model fitted (R² = 0.85) showed that wheat yield could be predicted by rainfall, the photothermal quotient, and mineralized N. The soil organic matter effect on crop yield seems to be mainly related to its nitrogen mineralization capacity. Using mineralized N as predictor would be a valuable tool for rating soil productivity.     

Prioritisation of novel pasture species for use in water-limited agriculture: a case study of <Emphasis Type="Italic">Cullen</Emphasis> in the Western Australian wheatbelt

In the face of a drying climate, identification of perennial pasture species suited to low-rainfall agricultural areas is needed. Effective prioritisation of putative pasture species may be possible through the use of desktop methods that are commonly employed to investigate the effect of climate change on native plant populations or the weed risk potential of plants. Species of Cullen Medik. native to Australia may be useful as perennial pasture legumes. It is not known, however, if species have adaptations for growth in low rainfall regions like the wheatbelt of Western Australia (WA). We tested the hypothesis that some Cullen species would be adapted to the climate and soils of the low-rainfall wheatbelt of WA using an analysis of soils and climate niche models of herbarium and germplasm records of 16 perennial, herbaceous and Australian Cullen species. We identified nine Cullen species that had some likely adaptation to the climate in the wheatbelt of WA, five of which (C. australasicum, C. cinereum, C. discolor, C. patens and C. tenax) had widespread adaptation to the climate and showed some adaptation to the soils of the wheatbelt of WA, making these priorities for further evaluation as perennial pasture species. The methodology is useful to identify species with likely best adaptation to low rainfall regions, generate expectations of where these may be most successful and to identify gaps in existing germplasm collections.     

利用相关矩阵法优化光谱指数的冬油菜氮素营养诊断

近年来高光谱技术由于无损和高效等优点成为了现代精准农业发展的必要手段方法。为实现冬油菜无损、快速的氮素盈亏诊断，该研究以连续两年(2022—2023年)不同覆盖及施氮处理下冬油菜蕾薹期采集的90份植物样品(地上部生物量和植株氮浓度)和高光谱实测数据为数据源，根据原始光谱和一阶微分(first-order differential,FD)光谱与氮营养指数(nitrogen nutrition index,NNI)的相关系数计算了8种(共16个)典型的光谱指数，随后利用相关矩阵法提取最佳光谱组合，并根据与NNI相关系数的计算结果筛选最优光谱指数，最后将最优光谱指数分为3组模型输入变量，分别采用支持向量机(support vector machine,SVM)、随机森林(random forest,RF)、极限学习机(extreme learning machine,ELM)和反向神经网络(back propagation neural network,BPNN)构建冬油菜蕾薹期NNI估算模型。结果表明一阶微分光谱指数与NNI的相关系数均大于原始光谱指数，3个组合选择的光谱指数与NNI的相关...     

Increased plant density with reduced nitrogen input can improve nitrogen use efficiency in winter wheat while maintaining grain yield

ABSTRACT

Plant density and nitrogen (N) input level have notable effects on root development, distribution in the soil profile, and in turn, N-uptake of winter wheat. Our study objectives were to identify whether a high yield can be maintained with a reduced N input by increasing plant density. Field studies were conducted during four successive seasons (2014–2015, 2015–2016, 2016–2017, and 2017–2018) using a widely planted cultivar, Tainong18. Two regimes of N fertilization (180 kg ha^?1 and 240 kg ha^?1) and three planting densities (135, 270, and 405 plants per m²) were used. Higher plant density led to increased root length density (RLD) and enhanced N uptake from the whole soil profile. The RLD in the soil profile at 0–1.2 m, 0–0.4 m, and 0.4–0.8 m decreased while in the 0.8–1.2 m layer it increased in response to reduced N input. The combined effects of higher plant density and lower N input resulted in reduced N uptake, a lower nitrogen nutrition index (NNI), unchanged grain yield, and improved N use efficiency. In conclusion, it is possible and sustainable to maintain a high wheat yield with reduced N input by increasing plant density.     

作物临界氮浓度稀释模型研究述评

作物临界氮浓度是作物达到最大生长的植株最小氮浓度。临界氮浓度随地上部植株干物质积累量增加而下降,可以用幂函数模型N_c=a×W_max^-b表示。已建立了数十种作物临界氮稀释模型,根据作物收获器官的特点,分为收获籽粒、收获鲜果实、收获块根块茎和收获地上部营养体4类,不同类型临界氮浓度稀释模型在模型参数和氮素诊断应用方面各有特点。临界氮浓度稀释模型除了植株临界氮浓度-植株干重这一典型形式外,还有器官临界氮浓度-器官干重、植株临界氮浓度-器官数量指标(叶片干重、茎鞘干重、LAI、叶面积持续期)等形式。因此,提出评价选择临界氮浓度稀释模型类型的基本原则。由于不同气候条件、不同作物类型,甚至同一作物不同品种的生育特性、氮素营养特性和干物质生产力差异很大,建立某一大类作物甚至某一种作物在各个气候区域的通用模型是困难的,应以一定生态区域某一作物特征相近品种类型作为建模基本单元。作物临界氮浓度稀释模型的应用包括计算氮营养指数(NNI)进行氮素营养诊断,计算临界氮积累量、亏缺量和氮肥需要量,预测作物产量和品质等。分析了以植株干物质重驱动的氮素...     

Relationship Between the Normalized SPAD Index and the Nitrogen Nutrition Index: Application to Durum Wheat

In a three-year field experiment in Toulouse (in Southwest France), two indicators of plant nitrogen (N) status were compared on five durum wheat cultivars: the normalized SPAD index and the nitrogen nutrition index (NNI). SPAD value is a non-destructive measurement of chlorophyll content from the last expanded leaf. The normalized SPAD index is expressed relative to SPAD reading on a fully fertilized crop. The NNI is calculated from the crop biomass and total plant N content using a universal N-dilution curve for wheat. The normalized SPAD index and NNI were closely related irrespective of year, cultivar, and growth stage. When N was a limiting factor, the SPAD index measured at anthesis predicted grain yield and protein content accurately. Unlike NNI, SPAD index cannot be used to predict these variables when wheat is over-fertilized.     

Relationship between spring barley productivity and growing management in Lithuania’s lowland

Purpose: The current study was aimed to analyse the occurrence of water and nitrogen stress in spring barley and estimate their effects on the crop performance under low-input and conventional management.

Materials and methods: Field experiments were conducted during 2007–2009 at the Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry on a sandy-loam soil. The management systems were: (a) conventional, with the application of fertilizers and pesticides adjusted to target 5 t ha^?1 grain yield; and (b) low-input, without fertilizers and pesticides. Biomass and nitrogen concentration, leaf area index, soil moisture, drainage water runoff and ground water table were measured periodically during the growing season.

Results: In all three experimental years, the annual precipitation was close or above the climate normal, but a large part of the rainfall (up to 310 mm) was lost through drainage contributing to the occurrence of temporary moisture deficit in late spring or summer. Water stress resulted in a lower spring barley biomass accumulation rate and lower biomass yield in the years characterized by sub-optimal rainfall distribution. Direct measurements of water retention in the soil and DSSAT model simulations gave relatively good indication of water stress occurrence. Under the low-input management, nitrogen nutrition level was a major constraint for spring barley biomass and grain yield formation.

Conclusions: Under Central Lithuania’s conditions, spring barley frequently experiences temporary water stress, because a relatively high proportion of annual precipitation is lost during the non-growing period. This crop can benefit from anticipated increased precipitation and carbon dioxide levels if adequately provided with nitrogen.     

Determining a critical nitrogen dilution curve for sugarcane

Adequate measurements of the nitrogen (N) concentration in the aboveground biomass of sugarcane throughout the growth cycle can be obtained using the critical N dilution curve (CNDC) concept, which provides an N‐nutrition index (NNI). The aim of this work was to determine the CNDC value for Brazilian sugarcane variety SP81‐3250, establish the critical concentration of N, and determine the NNI in the aboveground biomass throughout the cane plant and first ratoon crop cycles. The study was performed in three experimental areas located in São Paulo, Brazil, during the crop cycles of 2005/2006 (18‐month cane plant) and 2006/2007 (first ratoon). The plant cane crop was fertilized with treatments of 40, 80, or 120 kg N ha^–1 and a control treatment without N. After the plant cane harvest, rates of 0, 50, 100, or 150 kg N ha^–1 were applied to the control plot and the 120 kg N ha^–1–treatment plot in a split‐plot experimental design with four repetitions. Throughout both sugarcane cycles, measurements of aboveground biomass were used to determine the dry‐mass (DM) production and N concentration for each treatment. CNDC varied between the growth cycles, with a higher N concentration observed in the initial stages of the first ratoon and a lower N dilution observed throughout the plant cane cycle. The NNI value indicated excessive N storage in the initial stages and limiting concentrations at the end of the growth cycle. CNDC and NNI allow for the identification of the N‐nutrition variation rate and the period in which the nutrient concentration limits the production of aboveground biomass. The equations for the critical N (Ncr) level obtained in this study for plant cane (Ncr = 19.0 DM^–0.369) and ratoons (Ncr = 20.3 DM^–0.469) can potentially be used as N‐nutritional diagnostic parameters for sugarcane N nutrition.     

不同氮效率夏玉米临界氮浓度稀释模型与氮营养诊断

【目的】建立豫中地区玉米临界氮稀释曲线,比较不同氮素利用率玉米品种模型差异,探讨基于此的氮营养指数用于诊断、评价玉米氮素营养的可靠性,为实现玉米合理施用氮肥提供理论依据。【方法】以伟科702和中单909两个不同氮利用效率的品种为试验材料进行连续三年的田间定位试验,共设5个氮肥水平(0、120、180、240和360 kg/hm^2),分析不同施氮量对两个玉米品种拔节期、大喇叭口期、吐丝期、收获期干物质的影响,基于不同时期干物质和植株氮浓度建立两个品种临界氮稀释曲线,分析不同氮利用率品种玉米临界氮稀释曲线模型的差异和氮营养指数及其与相对地上部生物量和相对产量的关系。【结果】中单909的氮利用率显著高于伟科702。在各生育时期,两个玉米品种地上部生物量随施氮量变化表现为N0 –0.341,中单909 Nc=30.801DM^–0.370)具有很好的稳定性。相比中单909的模型参数,伟科702的参数a提高了15.70%,参数b降低了7.84%,且参数a变化值大于参数b。同一时期两个品种基于此模型的氮营养指数均随施氮量的增加而上升;施氮量低于180 kg/hm^2时,随着玉米生育时期的推进,氮营养指数随施氮量的增加呈先升高再降低的趋势,当施氮量超过240 kg/hm^2时,氮营养指数一直升高。氮营养指数与相对地上部生物量、相对产量相关性均达到显著水平。【结论】本文建立的豫中地区的两个品种玉米临界氮稀释曲线模型及氮营养指数,可以很好地诊断和评价玉米植株氮素营养状况。不同氮利用率品种间临界氮浓度稀释曲线模型参数存在差异,氮高效的品种具有较低的单位生物量氮浓度和较高的曲线斜率,其各时期临界氮浓度低于氮利用率低的品种。     

Nitrogen budget and relationships with riverine nitrogen exports of a dairy cattle farming catchment in eastern Hokkaido,Japan

Abstract

Dairy farming regions are important contributors of nitrogen (N) to surface waters. We evaluated the N budget and relationships to riverine N exports within the Shibetsu River catchment (SRC) of a dairy farming area in eastern Hokkaido, Japan. Five drainage basins with variable land-cover proportions within the SRC were also evaluated individually. We quantified the net N input (NNI) to the catchment from the difference between the input (atmospheric deposition, chemical fertilizers, N fixation by crops and imported food and feed) and the output (exported food and feed, ΔS _liv and ΔS _hu, which are the differences between input and output in livestock and human biomass, respectively) using statistical and measured data. Volatilized ammonia (NH₃) was assumed to be recycled within the catchment. The riverine export of N was quantified. Agricultural N was a dominant source of N to the SRC. Imported feed was the largest input (38.1?kg?N?ha^?1?year^?1), accounting for 44% of the total inputs, followed by chemical fertilizers (32.4?kg?N?ha^?1?year^?1) and N fixation by crops (13.4?kg?N?ha^?1?year^?1). The exported food and feed was 24.7?kg?N?ha^?1?year^?1 and the ΔS _liv and ΔS _hu values were 7.6 and 0.0?kg?N?ha^?1?year^?1, respectively. As a result, the NNI amounted to 54.6?kg?N?ha^?1?year^?1. The riverine export of total N from the five drainage basins correlated well with the NNI, accounting for 27% of the NNI. The fate of the missing NNI that was not measured as riverine export could possibly have been denitrified and/or retained within the SRC. A change in the estimate of the deposition rate of volatilized NH₃ from 100 to 0% redeposited would have decreased the NNI by 37%, although we believe that most NH₃ was likely to have been redeposited. The present study demonstrated that our focus should be on controlling agricultural N to reduce the impact of environmental pollution as well as on evaluating denitrification, N stocks in soil and the fate of NH₃ volatilization in the SRC.     

Identification of nutritional and environmental factors affecting sugarcane production in barbados

Abstract

Sugarcane production in Barbados has declined since the 1950s. Plant nutrition and fertilization deficiencies are generally believed to negatively influence yields in Barbados. The objective of this study was to identify nutritional and environmental factors related to sugarcane yields. Leaf analyses, respective crop yields, and other data were collected from the Barbados Sugar Industry Ltd. during the period 1985–1990. The database was constructed from 2,853 site observations, consisting of crop cane yield (Mt/ha), soil grouping, ecological grouping, growing elevation, and leaf tissue analysis [nitrogen (N), phosphorus (P), potassium (K)]. Simple mean separation and tree‐based regression were used to identify nutritional and environmental factors associated with sugarcane yields. Twenty‐three environments were delineated by tree‐based regression, in which plant nutrient deficiencies (i.e., yield limiting) were identified. One environment described N‐deficient conditions, four environments described P‐deficient conditions, and five environments described K‐deficient conditions. Different critical leaf nutrient concentrations were related to yields. A single nutrient norm under different environments may be misleading. If current fertilizer recommendations are adhered to by growers in Barbados, attention to additional fertilization should be given only under these environments.