利用叶绿素计(SPAD-502)诊断水稻氮素营养和推荐追肥的研究进展

叶绿素计(SPAD-502)在监测水稻氮素营养水平和及时提供追肥所需的信息方面有快速、简便、无损的特点,但其精度常受多种因素的影响。本文分析了影响利用SPAD-502叶绿素计诊断水稻氮素营养和推荐追肥精度的水稻品种、生育时期、测定叶位、测定叶片的位点、生态环境等因素。并综述了通过量化SPAD读数与氮的关系,提高诊断水稻氮素营养精度;通过量化SPAD读数与追肥关系,提高SPAD-502叶绿素计诊断法推荐施肥精度的研究现状;提出进一步提高利用SPAD-502叶绿素计诊断水稻氮素营养状况与推荐追肥精度尚需解决的几个问题。     

膜下滴灌棉花氮素推荐施肥模型的研究

研究应用叶绿素仪（SPAD-502）在膜下滴灌条件下的棉花氮肥推荐。试验于2006年在石河子乌兰乌苏农业气象实验站进行,以新陆早24为材料。结果表明,不同叶位的叶片含氮量、SPAD值及叶片不同部位的SPAD值存在明显差异,SPAD值与叶绿素含量、叶片含氮量、单株吸氮量等均有较好的相关性;倒四叶的叶尖部位适合作为测试部位。盛蕾期、花期、盛花期和铃期倒四叶SPAD值与施氮量之间呈极显著线性相关;各生育期SPAD值与产量也具极显著相关。滴灌条件下最高籽棉产量为4686.5 kg/hm2,对应的施肥量为293.1 kg/hm2;最大利润（经济最佳）施肥量为207.33 kg/hm2,对应的最佳产量为4565.9 kg/hm2。各生育期SPAD的临界值分别为60.5、60.0、60.8和59.1。盛蕾期、花期、盛花期和铃期SPAD值每变动一格推荐施肥量分别为10.81、8.46、13.42和6.29 kg/hm2。     

烤烟氮素营养诊断及精准施肥模式研究

为解决烤烟生产中存在过高施氮或不合理的施肥技术措施致使烟叶产质量下降和氮素利用效率低下等突出问题,该研究于2008-2010年在广东韶关烟草产区以烤烟品种K326为材料,研究不同施氮水平下不同叶位及叶片不同位置上的叶绿素仪测定值(SPAD值)、叶绿素含量、总氮含量的变化特征及其与产质量的相互关系,分析实时氮肥管理(RTNM)模式下不同SPAD施肥阈值对烟草产质量及氮肥利用率的影响,结果表明:顶三叶的叶中位置SPAD值与叶片叶绿素含量、总氮含量的相关性最好,且变异系数小,是较为理想的指示叶或参照叶;获得较好产质量烤烟时的SPAD值在伸根期和旺长期的阈值范围为38.3～47.2。在设置不同SPAD阈值的RTNM模式下,SPAD阈值40.5~43范围内(氮肥用量为75～110kg/hm2)能获得较高的烟叶产量、产值,最高产量和产值分别为2844.09kg/hm2和26989.24元/hm2,烟叶化学成分较为协调。此外,通过与农民习惯施肥模式(167.8kg/hm2)相比较,在SPAD设定阈值为43的RTNM模式下,相应的氮肥用量为110kg/hm2,氮肥农学利用率和吸收利用率分别提高53.0%、46.5%,产值提高了7.4%,调制后烟叶的淀粉、总氮、烟碱含量显著下降,烟叶化学成分更为协调,内在质量较好。     

不同施氮量及基追比例对玉米冠层生理性状和产量的影响

以加拿大魁北克地区推广的玉米品种Pioneer 38B84为材料,研究不同施氮量和基追比例对玉米最上一片全展开叶SPAD值、Dualex值、净光合速率(PN)、叶面积指数(LAI)、地上部生物量、冠层叶绿素密度(SPAD×LAI)、冠层光合能力(PN×LAI)以及产量的影响。试验设5个处理:N0(基0+追0)、N20+93(基20 kg/hm2+追93 kg/hm2)、N45+68(基45 kg/hm2+追68 kg/hm2)、N113(基113 kg/hm2+追0)和SAT225[基225(播种时施氮45 kg/hm2,播种后10 d再沟施180 kg/hm2)+追0],完全随机区组设计,重复4次,基本苗为79000株/hm2。结果表明,追肥前,叶片SPAD值、PN、LAI、地上部生物量、SPAD×LAI及PN×LAI均随基肥氮量的增加而增加,Dualex值则降低。同等施氮量下,基肥配合追肥显著提高叶片SPAD值,而追肥对叶片Dualex值和PN无显著影响。虽然基肥配合追肥处理的LAI、地上部生物量、SPAD×LAI、PN×LAI在追肥后均显著低于氮肥一次性基施,但显著提高了玉米产量。基施氮肥20 kg/hm2与45 kg/hm2处理之间玉米产量无差异,但前者过早地表现出缺氮。总施氮量为113 kg/hm2时,其SPAD值、Dualex值、PN、LAI、地上部生物量、SPAD×LAI以及PN×LAI等指标在出苗后256~0 d与SAT225处理差异不显著,但产量却显著低于SAT225处理。本试验条件下,基肥量45 kg/hm2能较好地满足玉米前期生长,但总施氮量113 kg/hm2不能满足玉米全生育期的需求,需要进一步地评估适宜的施氮量。同等施氮量下,基肥配合追肥显著提高玉米产量;SPAD值和Dualex值均与玉米植株氮含量显著相关,SPAD和Dualex可以作为实时快速指导玉米追肥的有效工具。     

基于SPAD-502与GreenSeeker的冬小麦氮营养诊断研究

用GreenSeeker和SPAD-502测定了不同氮素处理的冬小麦冠层NDVI与叶片SPAD值, 分析了它们与叶片全氮、叶绿素含量及产量间的关系。结果表明: 冬小麦抽穗期SPAD值和NDVI值均与叶绿素含量呈极显著正相关; 除抽穗期和返青期外, SPAD值与叶氮含量、叶绿素含量的相关系数在其余各生育期均达到显著或极显著水平; NDVI值与叶氮含量、叶绿素含量在拔节期、乳熟期的相关性同SPAD值一致; SPAD值可以进行叶绿素的诊断, NDVI值可以进行氮的诊断。氮营养诊断时期应该选择拔节期。通过回归建立了基于SPAD值、NDVI值的产量估测模型, 可以通过SPAD值、NDVI值对冬小麦产量进行估算。     

盐渍化农田不同施氮水平对向日葵SPAD值的影响

以内蒙古河套灌区主要经济作物向日葵为研究对象,对不同盐渍化程度(S0:0.25%,S1:0.25%~0.5%,S2:0.5%)和施氮量(N)水平(N0:0 kg/hm2、N1:90 kg/hm2、N2:135 kg/hm2、N3:180 kg/hm2)下向日葵相对叶绿素含量(SPAD值)在不同生育期的变化特征进行分析。结果显示,SPAD值可以反映出向日葵的氮素供给状况,其在蕾期和花期与地上部分干物质量(蕾期R=0.576,花期R=0.655)和籽粒产量(蕾期R=0.774,花期R=0.758)均有显著的相关关系。向日葵SPAD值在不同生育期受到盐分和施氮量水平不同程度的影响。在轻度盐渍化程度(S0)下,N1水平施氮量下的SPAD值在进入蕾期后均仅次于N3水平,该水平的施氮量可满足该环境中向日葵的生长;在中度盐渍化程度(S1)下,当施氮量水平从N1增加到N2时,SPAD值有明显的增加。在重度盐渍化程度(S2)下,各施氮肥处理的SPAD值相比于不施氮肥的N0水平,不仅没有显著上升,反而有部分出现明显下降。据此,提出了针对不同盐渍化程度农田的推荐向日葵氮肥施用量(S0:90 kg/hm2,S1:135 kg/hm2,S2:0 kg/hm2),为经济合理地施用氮肥提供依据。     

应用叶绿素仪诊断冬小麦氮营养状况的研究

利用叶绿素仪SPAD-502进行田间快速测定,并对作物进行氮肥推荐。结果表明,冬小麦应用叶绿素仪监测氮营养状况的测定部位为最上部完全展开叶的中部,该部位叶绿素仪测定值与作物全氮、施氮量及作物产量之间均有较好的相关性。作物品种对叶绿素测定结果影响很大,需要通过相对叶绿素仪读数的方法对其进行校正。     

硝酸盐反射仪和SPAD法对玉米氮素营养诊断的比较

精准的营养诊断是了解作物氮素营养及推荐施肥的基础。本文在田间滴灌条件下利用SPAD叶绿素仪(SPAD-502 Plus)和硝酸盐反射仪(RQ flex10)两种诊断方法对玉米关键生育时期的氮素营养诊断进行研究,旨在筛选出适宜的诊断方法,并依据诊断值建立滴灌玉米不同生育时期的施肥模型。试验设置0 kg(N)·hm~(-2)(N0)、225 kg(N)·hm~(-2)(N225)、330 kg(N)·hm~(-2)(N330)、435 kg(N)·hm~(-2)(N435)和540 kg(N)·hm~(-2)(N540)5个施氮水平,在不同生育时期测定了玉米叶片SPAD值和叶鞘NO_3~-含量,并分别与施氮量、植株全氮含量、产量进行方程拟合,比较两种诊断方法对玉米氮素营养的响应。研究结果表明:1)玉米叶片SPAD值和叶鞘NO_3~-含量均随施氮量的增加而显著升高,且在拔节期对施氮量的响应最敏感。叶鞘NO_3~-含量对施氮量变化的响应较SPAD值大,其与施氮量及玉米产量的拟合度均高于SPAD值,说明硝酸盐反射仪法对滴灌玉米氮素丰缺的反应更灵敏。2)玉米全氮含量与叶片SPAD值呈显著线性关系,而与叶鞘NO_3~-含量则以线性加平台表示。当叶鞘NO_3~-含量小于186 mg·L~(-1)时,植株全氮与NO_3~-间呈显著线性相关;当叶鞘NO_3~-含量大于186 mg·L~(-1)时,植株全氮随NO_3~-含量增加趋于不变。3)本农作区滴灌玉米最佳经济施氮量为402.5 kg·hm~(-2),对应的玉米产量为17 049 kg·hm~(-2)。玉米拔节期、抽雄吐丝期和灌浆期的临界叶鞘NO_3~-含量分别为729.3 mg·L~(-1)、536 mg·L~(-1)和81.2 mg·L~(-1)。SPAD叶绿素仪和硝酸盐反射仪均可对滴灌玉米进行氮素营养诊断,但硝酸盐速测值能更敏感地反映氮素丰缺状况,基于硝酸盐反射法进行作物氮素营养诊断及推荐施肥具有较好的准确性与适用性。     

氮素调控对寒地玉米氮素吸收与叶片SPAD值影响的初探

由于氮肥分配比例和施用时期不当,以及没有确定氮肥追肥时期的量化指标等原因,造成了氮肥利用率较低。试验通过对玉米进行氮素(追肥时期、追肥量)的优化,研究不同叶龄期玉米叶片叶绿素(SPAD值)及氮素积累动态的变化规律,确定玉米追肥时期的叶绿素阈值,对玉米进行调控和优化定量施肥。结果表明,玉米最佳追氮时期为十叶期,在此时期,玉米穗位叶SPAD值虽然逐渐降低,但上位叶在抽雄期达到最大,然后下降。玉米全株氮素积累逐渐增加。在十叶期追氮,高氮处理(150 kg/hm2)玉米的产量最高。     

应用多酚–叶绿素仪监测棉花氮素营养状况研究

  【目的】  通过田间试验,研究使用多酚–叶绿素仪对棉花进行快速无损氮素营养诊断适宜的指标。  【方法】  田间试验在新疆石河子市进行,设3个施氮处理,分别为施纯N 0、180和240 kg/hm2,分别用N0、N180和N240表示。所有氮肥分5次随滴灌施入,每次施肥后3天,利用多酚–叶绿素仪 (Dualex-4) 和SPAD叶绿素仪分别测定20株棉花叶片的氮平衡指数 (NBI)、Chl值和SPAD值,同步采样测定棉花叶片全氮含量,及0—20 cm、0—40 cm和0—60 cm土层硝态氮含量。  【结果】  随着施氮量的增加棉花叶片全氮含量和土壤硝态氮含量均显著增加。其中,0—40 cm土层硝态氮含量与棉花叶片全氮含量关系最密切。增加氮肥施用量,棉花叶片氮素营养诊断指标NBI、Chl值和SPAD值均显著增加。棉花叶片NBI、Chl和SPAD与叶片全氮含量均呈极显著正相关关系,且相关系数 (r) 均达到0.8以上。相关性模型校验结果表明,棉花叶片全氮含量实测值与预测值的平均相对误差 (RE) 分别为–4.0% (NBI)、–3.1% (Chl) 和–5.7% (SAPD)。其中,氮平衡指数 (NBI) 模型对棉花叶片全氮含量的预测精度最高,与实测值的相关系数达到了0.9143,平均绝对百分比误差 (MAPE) 为6.91%;标准均方根误差 (nRMSE) 为8.21%。棉花叶片NBI、Chl和SPAD与土壤硝态氮的模型决定系数表现为NBI > Chl > SPAD。模型校验分析表明,NBI模型与0—40 cm土层硝态氮实测含量的相关性最高,相关系数为0.9116,预测值与实测值的MAPE和nRMSE分别为14.11%和17.88%。  【结论】  应用多酚–叶绿素仪监测棉花氮素营养,氮平衡指数 (NBI) 与棉花叶片氮含量和0—40 cm土层硝态氮含量的相关性最高,预测值与实测值的误差仅为6.91%和14.11%,可以满足膜下滴灌条件下棉花氮素营养的快速诊断需求。     

Assessing Variations in SPAD‐502 Chlorophyll Meter Measurements and Their Relationships with Nutrient Content of Trembling Aspen Foliage

Abstract

The relative chlorophyll content in leaves estimated by the SPAD‐502 chlorophyll meter can be an efficient way to evaluate plant nitrogen (N) status in many crops and some tree species. In this study, the SPAD meter was used to look for relationships between relative leaf chlorophyll content and leaf nutrient concentration in trembling aspen. The variations in leaf chlorophyll measurements were also evaluated by using three sampling times and three measurement techniques. Hypothetical experimental designs were created to achieve better design efficiency. The best representation of overall leaf chlorophyll was found when six SPAD readings were taken at different locations on each leaf. There was a positive correlation between overall leaf N and estimated chlorophyll content, especially in the top part of the trees. Overall, this study suggested that the SPAD meter can give an estimation of trembling aspen nutritional status, especially if the differential partitioning of N within trees is considered.     

Chlorophyll meter predicts nitrogen status of tall fescue

The nitrogen (N) status of a crop can be used to predict yield and supplemental N fertilizer requirements, and rapid techniques for evaluating the N status of crops are needed. A study was conducted to determine the feasibility of using a hand held chlorophyll meter (SPAD 502, Minolta Co. Ltd., Japan) to monitor N status of tall fescue (Festuca arundinacea Schreb.). Four diverse tall fescue genotypes were grown at three locations in Alabama and fertilized at four N‐rates from 0 to 336 kg ha^‐1. A similar experiment was conducted in the greenhouse using soil from the same field sites. Chlorophyll meter readings (SPAD) were taken, and extractable chlorophyll content, tissue N concentration and dry matter yield were determined at harvest. SPAD, extractable chlorophyll content, tissue N concentration, and dry matter yield increased quadratically (0.67 < R² < 0.99) with increasing N fertilization in both experiments. All genotypes responded similarly to applied N, with some differences in magnitude. Relationships between SPAD meter readings and extractable chlorophyll and tissue N concentrations were linear with r² > 0.95. An additional independent variable, the square root of the inverse of SPAD, lowered the residual mean square by 11 and 16%, respectively, for tissue‐N and chlorophyll concentrations, but did not increase the R². This would be preferred for predictive purposes. Tissue N concentrations at higher N‐rates were sufficient for maximum yield which occurred at 290 and 248 kg N ha^‐1 for greenhouse and field, respectively, but were lower than previously reported sufficiency values. The chlorophyll meter is an easy and efficient method of detecting tall fescue N status.     

Photosynthesis,Chlorophylls, and SPAD Readings in Coffee Leaves in Relation to Nitrogen Supply

The export of nitrogen (N) from senescent plant parts is important for the efficient use of this macronutrient. The objective of this study was to establish correlations among the photosynthetic pigment content, total N, and the photosynthetic variables with the SPAD‐502 readings in Coffea arabica leaves. Correlations were established among the chlorophyll content, N content, and chlorophyll a and b with SPAD‐502 readings taken on coffee leaves at different months. The results show that all variables decreased with time. However, correlation increased linearly with N doses. Total chlorophyll presented a direct linear correlation with readings of the portable chlorophyll meter. The SPAD readings have shown to be a good tool to diagnose the integrity of the photosynthetic system in coffee leaves. Thus, the portable chlorophyll SPAD‐502 instrument can be used to evaluate the N status and can also help to evaluate the photosynthetic process in coffee plants.     

SEASONAL VARIATION AND THRESHOLD VALUES FOR CHLOROPHYLL METER READINGS ON LEAVES OF POTATO CULTIVARS

Chlorophyll meter readings below a threshold value would indicate the necessity to supply nitrogen (N) to the crop. This study aimed to determine threshold values for chlorophyll meter (SPAD) and nitrogen (N) rate effects on SPAD leaf measurements of potato cultivars through the crop cycle. Five N rates (0, 50, 100, 200, and 300 kg ha^?1) were evaluated in a randomized block design, with four repetitions. SPAD index was measured on the oldest (OL) and on the fourth leaf from the apex (FL) at 7, 14, 21, 28, 35, and 49 days after the emergence of 90% of the plants in the plots. SPAD values decreased with plant age and were influenced by N rates and leaf position. At 21 DAE, the SPAD threshold values on FL were 43.0, 44.6, 46.5, and 50.0 for ‘Agata’, ‘Monalisa’, ‘Atlantic’, and ‘Asterix’, respectively. The corresponding values were 41.9, 43.5, 49.9, and 49.9 on OL. Plant age and leaf position should be standardized for the assessment of SPAD threshold values to diagnose nitrogen status of potato cultivars.     

叶绿素仪在氮肥推荐中的应用研究进展

叶绿素仪(Chlorophyll.meter)是近年来欧美一些国家在推荐施氮中开始使用的一种新型便携式仪器。这种仪器以叶绿素对红光和近红外光的不同吸收特性为原理来测定植物叶片的相对叶绿素含量,通过叶绿素与叶片全氮的关系来反映作物的氮营养状况,进而确定作物是否缺氮。这种新型仪器的使用为简便、快速、准确地进行氮肥推荐提供了一种新的思路。因此,通过研究不同作物,不同种植条件下叶绿素仪测定值与作物叶片全氮、作物产量之间的相关性,确定叶绿素仪测定值的临界水平,以及不同作物的测定部位、样品采集数量及影响测定准确性的因素,使这种技术尽快地应用于田间生产,有助于推动我国推荐施氮技术的进步。     

INTER-RELATIONSHIPS OF APPLIED NITROGEN,SPAD, AND YIELD OF LEAFY AND NON-LEAFY MAIZE GENOTYPES

The SPAD chlorophyll meter was found to be a reliable, quick, and non-destructive tool used for directly measuring leaf chlorophyll and indirectly assessing the proportional parameter of leaf, and by extension, plant nitrogen (N) status. The meter has been used successfully to assess leaf N in conventional maize crops, but it has not been used with new maize (Zea mays L.) genotypes containing leafy (L) and reduced stature (RS) traits. SPAD meter readings were collected on the uppermost fully developed leaves (before silking) and on the ear leaf (after silking) of field grown maize genotypes with and without the L and RS traits. The experiment was conducted during 1996 and 1997 at two sites in Eastern Canada (Ottawa and Montreal). At each site in each year, a split plot arrangement of two treatment factors was used in a randomized complete block design with four blocks. The main plot treatments were levels of N (0, 85, 170, and 255 kg ha^?1), with six maize genotypes as subplot treatments. The hybrids included: (i) leafy reduced-stature, LRS, (ii) non-leafy normal stature, NLNS, (iii) leafy normal stature, (LNS), (iv) non-leafy reduced-stature, NLRS, (v) conventional commercial hybrids, Pioneer 3905 as the hybrid check for late maturity, and (vi) Pioneer 3979, a check for early maturity. The hybrids were chosen on the basis of their contrasting canopies and root architecture. The SPAD meter readings were collected on the same five plant genotypes over time (six times per site per year, except four times for the Ottawa site in 1997). All genotypes showed increasing meter reading values as plants aged until silking. In general, SPAD meter readings increased as N fertilization level increased at each measurement date for both sites and years. In general, LNS and P3905 hybrids showed greater SPAD meter readings than other hybrids at all sampling dates for both sites and growing seasons. Applied N rates were significantly correlated with the SPAD meter readings. More highly significant relationships were found for N fertilizer levels and SPAD meter readings for the hybrids in 1997 than for the hybrids in 1996. For the Montreal site in 1997, LRS, LNS and P3905 hybrids were among those showing the highest r values between N level and SPAD readings. The correlation coefficients between SPAD readings and grain yield were generally lower. However, the NLNS hybrid had a high SPAD-yield correlation at the Macdonald site in 1997.     

Correlation of leaf chlorophyll readings and stem nitrate concentrations in peppermint

Abstract

The SPAD chlorophyll meter appears promising for rapid, on‐farm analysis of crop nitrogen (N) status. Leaf SPAD chlorophyll levels have been correlated with total leaf N concentrations, but it has not been determined how they relate to other widely applied N diagnoses such as petiole or stem nitrate (NO₃) analysis. Our objective was to examine the relationship between leaf SPAD readings and stem NO₃ levels in peppermint (Mentha piperita L.). Upper canopy SPAD chlorophyll and stem NO₃ concentrations were determined weekly during two seasons for peppermint grown with variable N inputs. Leaf SPAD levels exhibited significant linear‐plateau responses with respect to stem NO₃, indicating that SPAD readings do not respond to luxury N consumption. The meter is therefore promising for the detection of crop N deficiencies by comparison of production fields to well fertilized plots or strips. Break‐points in the linear‐plateau regressions describe saturation concentrations of stem NO₃ with respect to leaf SPAD levels peaking at 12,000 mg NO₃‐N/kg in mid to late July and declining later in the season. The SPAD meter may be applied directly to N management by use of reference plots or it may be used as a tool to aid in determination of criteria for other diagnoses such as tissue NO₃.     

华北地区采用无机氮测试和植株速测进行夏玉米氮肥推荐

A field experiment with a split-plot design was carried out at Dongbeiwang Farm in Beijing Municipality to establish reliable N fertilizer recommendation indices for summer maize (Zea mays L.) in northern China using the soil Nmin(mineral N) test as well as the plant nitrate and SPAD (portable chlorophyll meter readings) tests. The results showed that Nrnin sollwert (NS) 60 kg N ha^-1 at the third leaf stage and N rate of 40 to 120 kg N ha^-1 at the tenth leaf stage could meet the N requirement of summer maize with a target yield of 5.5-6 t ha^-1. Sap nitrate concentrations and SPAD chlorophyll meter readings in the latest expanded maize leaves at the tenth leaf stage were positively correlated with NS levels, indicating that plant nitrate and SPAD tests reflected the N nutritional status of maize well. Considering that winter wheat subsequently utilized N after the summer maize harvest, the 0-90 cm soil Nmin (74 kg N ha^-1) and apparent N loss (12 kg N ha^-1) in the NS60＋40 treatment were controlled at environmentally acceptable levels. Therefore NS60＋40, giving a total N supply of 100 kg N ha^-1, was considered the optimal N fertilizer input for summer maize under these experimental conditions.     

Ammonium concentration in solution affects chlorophyll meter readings in tomato leaves

Abstract

Combinations of NH₄‐N:NO₃‐N usually result in higher tomato (Lycopersicon esculentum Mill.) yields than when either form of nitrogen (N) was used alone. Leaf chlorophyll content is closely related to leaf N content, but the effect of the NH₄‐N:NO₃‐N ratio on leaf greenness was not clear. The objective of this study was to determine the influence of NH₄‐N:NO₃‐N ratios on chlorophyll meter (SPAD) readings, and evaluate the meter as a N status estimator and tomato yield predictor in greenhouse production systems. Fruit yield and SPAD readings increased as the amount of NH₄‐N in solution increased up to 25%, while higher ratios of NH₄‐N resulted in a decline in both. The N concentration in tomato leaves increased as concentration of NH₄‐N in solution increased. Fruit yield increased as chlorophyll readings increased. SPAD readings, total N in leaves, fresh weight of shoots, and fruit yield all showed a quadratic response to NH₄‐N, reaching a peak at 25 or 50% of N as NH₄‐N. SPAD readings taken at the vegetative and flowering stages of growth had the highest correlation (r²=0.54) with N concentration in leaves, but this could not be used as a reliable estimate of N status and fruit yield. Lack of correspondence between high N concentration values and fruit yield indicated a detrimental effect of NH₄‐N on chlorophyll molecules or chloroplast structure. The SPAD readings, however, may be used to determine the optimum NH₄‐N concentration in solution to maximize fruit yield.     

Estimation of Chlorophyll Contents by Correlations between SPAD‐502 Meter and Chroma Meter in Butterhead Lettuce

Abstract

Chlorophyll content of butterhead lettuce leaves was estimated by correlations between the Minolta SPAD‐502 and Minolta chroma meter CR 300. The SPAD‐502 readings and extractable chlorophyll (Chl a, Chl b, and total Chlorophyll) contents were related. High linear correlations were obtained for chlorophyll a (R²=0.90), chlorophyll b (R²=0.85), and total chlorophyll (R²=0.92). After that, during the growth cycle of butterhead lettuce grown in soilless culture, leaves were selected and SPAD‐502 and chroma meter readings were made. Finally, correlations between SPAD‐502 readings and leaf color (L*, a*, b*, C*, and hue angle) determined by the chroma meter were calculated. Hue angle (H°; R²=0.75) and lightness index (L*; R²=0.68) were the parameters that better relate with SPAD‐502 readings, so these parameters can also be used for rapid and nondestructive estimates of leaf chlorophyll in situ.