Determination of cotton nitrogen status with a handheld chlorophyll meter

The ability of a hand‐held chlorophyll meter (SPAD‐502 Chlorophyll Meter³, Minolta Camera Co., Ltd., Japan) to determine the N status of cotton (Gossypium hirsutum L.) was studied at field sites in Alabama and Missouri. Meter readings on the uppermost fully‐expanded leaf were compared to leaf‐blade N and petiole NO₃‐N at first square, first bloom and midbloom as to their seed cotton yield predictive capability. Nitrogen was applied at rates of 0, 45, 90, 135, 180 and 225 kg ha^‐1 to establish a range of cotton chlorophyll levels, tissue N concentrations, and seed cotton yields. A typical curvilinear cotton yield response to N fertilizer was observed in Alabama experiments.

Because of adverse weather conditions, cotton yield in Missouri experiments did not respond to N. Chlorophyll meter readings were significantly correlated to leaf‐blade N concentration at all three stages of growth for all experiments. In Alabama, chlorophyll meter readings compared favorably to leaf‐blade N and petiole NO₃‐N with respect to their seed cotton yield predictive capability at all three stages of growth. It appears that hand‐held chlorophyll meters would be as reliable as leaf‐blade N and petiole NO₃‐N for predicting supplemental N fertilization requirements of cotton. However, more research will be required prior to use of chlorophyll meter readings for routine cotton‐N recommendation purposes.     

Using a chlorophyll meter to manage nitrogen applications to corn with high nitrate irrigation water

Abstract

Chlorophyll meters can aid in measuring the nitrogen (N) status of corn (Zea mays), but will the use of chlorophyll meters decrease total N use or increase corn grain yield? Use of a fully fertilized reference strip with a chlorophyll meter (SPAD 502) is an accepted management strategy. The critical level of relative chlorophyll necessary to trigger supplement N is uncertain. To determine the impact of using a 96 or 92% critical level of chlorophyll readings relative to a fully fertilized reference strip, 0 and 112 N kg ha^‐1 were applied at planting for three years. Specific plots were fertilized with an additional 56 kg N ha^‐1 whenever the meter reading on those plots was below either 96 or 92% of the reference area. The experiment was conducted on two Typic Haplustolls and an Entic Haplustoll. Irrigation water contained nitrate ranging from 20 to 38 mg L^‐1. Irrigation water supplied from 43 to 120 kg N ha^‐1 season^‐1. For all treatments that received N‐supplements based on the chlorophyll meter, yields were statistically the same. The chlorophyll meter is a useful management tool to help schedule N applications, when irrigation water is contaminated with nitrate since use of the chlorophyll meter prevented any yield limiting N deficiencies.     

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.     

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.     

Leaf chlorophyll readings as an indicator of nitrogen status and yield of spinach (Spinacia oleracea L.) grown in soils amended with Luecaena leucocephala prunings

A field study was conducted to evaluate the nitrogen status and yield of spinach grown in soils amended with prunings of Leucaena leucocephala, (applied at a rate of 3, 5, 7 or 11 t ha^?1). A ‘no fertilizer’ 0 nitrogen (N) and 150 kg N ha^?1 (recommended) were the control treatments. SPAD readings were recorded for the top six leaves. Nitrogen sufficiency indices were used to indicate the N status of plants. Application of L. leucocephala prunings increased spinach yields (8.98–13.86 t DM ha^?1) relative to the 0N treatment (1.35 t DM ha^?1) and yields increased with increasing rate of pruning application. SPAD readings showed a linear increase with the increase in applied prunings. There was preferential distribution of N to upper leaves. The relationship between shoot N concentration and SPAD readings was linear and strongest for the top three leaves (r² = 0.84–0.92). The results indicate the potential of chlorophyll meter readings in assessing N status of leafy vegetables grown on soils amended with different levels of legume tree prunings.     

Tomato leaf chlorophyll meter readings as affected by variety,nitrogen form,and nighttime nutrient solution strength

Leaf chlorophyll content is closely related to leaf nitrogen (N) content, so it is reasonable to assume that ammonium‐N (NH₄‐N): nitrate‐N (NO₃‐N) ratio in the nutrient solution used to grow tomatoes (Lycopersicon esculentum Mill.) hydroponically may affect leaf greenness, and consequently chlorophyll meter (SPAD) readings. It has also been shown that increasing nutrient solution strength (NSS) increases tomato productivity, but there are no reports regarding how NSS affects SPAD readings under greenhouse conditions. Genotype may also influence SPAD readings, and standardization for cultivar and sampling time may be needed. The objective of this study was to characterize SPAD readings for five tomato cultivars and SPAD reading response to a combination of two NSS (1X and 4X Steiner solution strength daily applied 18 days after transplanting at 7 p.m.) and two concentrations of NH₄‐N in solution (0 and 25%) in order to evaluate the potential of SPAD readings as a tomato yield predictor in greenhouse production systems. The SPAD readings were not uniform across tomato varieties tested, being consistently higher for ‘Max’ and lower for the other varieties. Initially, SPAD readings for tomato varieties used in this study were low at the vegetative stage, and increased up to 40 DAT, but subsequently decreased at 49 DAT, or the fruit set of the first and second clusters. After this time, SPAD readings showed no variation. Chlorophyll meter readings for ‘Max’ were higher in the top plant layers, but decreased in the top plant layer of the other tomato varieties. The SPAD readings were higher for plants supplied with 25% NH₄‐N than those without NH₄‐N in solution, but the use of a nighttime nutrient solution did not affect SPAD readings. None of the possible interactions among tomato variety, NH₄‐N: NO₃‐N ratio, and NSS were consistently significant.     

The crop as indicator for sidedress nitrogen demand in sugar beet production — limitations and perspectives

In 2‐years field experiments near Nienstädt (60 km west of Hannover, northern Germany), the effects of rate and timing of nitrogen (N) application on leaf N‐concentration, leaf greenness (SPAD chlorophyll meter readings), canopy greenness (canopy light reflectance), leaf area development, photosynthetic activity of leaves, and yield and quality of sugar beet were studied. In 1999 (pre‐planting soil mineral N: 15 kg ha^—1), N fertilizer was applied at rates of 0, 105, 125, 145, 165 and 205 kg N ha^—1. In 2000 (pre‐planting soil mineral N: 60 kg ha^—1), an N rate of 100 kg ha^—1 was applied at planting (100/0/0/0) or split applied at planting and 8 (60/40/0/0), 12 (60/0/40/0), and 16 (60/0/0/40) weeks after planting (WAP), respectively. In both years, canopy greenness as indicated by ”︁sensor values” (a combination of the reflectance of visible and near infrared light) changed with crop age. However, at each time of measurement, sensor values precisely reflected the different N application treatments and were significantly correlated with leaf N‐concentrations and SPAD chlorophyll meter readings. Beet yield and processed white sugar yield increased up to an N supply (fertilizer N + pre‐planting soil mineral N) of 160 kg ha^—1. Split N application slightly retarded leaf growth but had no effect on photosynthetic activity per unit leaf area. Beet yield and beet quality were not systematically affected by the timing of N application. Certain application schemes tended to favor either beet yield or beet quality, resulting in similar processed white sugar yields. Our data suggest that moderate N topdressing can be integrated in site‐specific N management systems in sugar beet production. Canopy light reflectance might serve as a useful diagnostic tool to assess the N status and sidedress N demand of sugar beets. However, due to changing sensor values over time, on‐site calibration (using established standard methods or reference plots receiving extra N at planting) will be necessary. The applicability of this approach has to be tested in further field studies.<?show $6#>     

Evaluation of the Minolta SPAD‐502 chlorophyll meter for nitrogen management in corn

The field study investigated the relationship of Minolta SPAD 502 (SPAD) readings to applied nitrogen (N) fertilizer rate, corn (Zea mays L.) yield, and leaf N concentration. The experiment was conducted on a total of six sites in Illinois during 1991 and 1992. Ten different open pedigree corn hybrids were grown at a final population of 65,000 plants ha^‐1. Nitrogen was applied at four rates(0, 90, 180, and 270 kgN ha^‐1) as 28% liquid N solution. Significant main effects of environment (E), and hybrid (H), and E x H interaction were detected for all measured parameters. SPAD readings and leaf N concentration at all sampling times (V7, R1, and R4) as well as grain N concentration were affected by N fertilizer rate. Maximum mean grain yield and maximum grain N concentration were obtained at 110 and 195 kg N ha^‐1, respectively. At all sampling times the correlation of SPAD readings to N fertilizer rate were low but significant (R=0.22 at V7 and R1, R=0.11 at R4). SPAD correlation to corresponding leaf N concentration improved over time. The Pearson correlation was R=0.33 at V7 and increased to R=0.78 at R4. The SPAD meter did a good job at providing a measure of the relative greenness of living leaves at a specific point in time. Chlorophyll readings can therefore be useful in detecting N deficiencies in growing crops. But, the SPAD meter cannot be used to make accurate predictions of how much fertilizer N will be needed by a crop during the future growing season. We conclude then that the SPAD meter will be most useful as a diagnostic aid rather than a tool for N management in corn.     

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.     

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.     

TOMATO LEAF CHLOROPHYLL METER READINGS AS AFFECTED BY VARIETY,NITROGEN FORM,AND NIGHTTIME NUTRIENT SOLUTION STRENGTH

ABSTRACT

Leaf chlorophyll content is closely related to leaf nitrogen (N) content, so it is reasonable to assume that NH₄–N:NO₃–N ratio in the nutrient solution used to grow tomatoes (Lycopersicon esculentum Mill.) hydroponically may affect leaf greenness, and consequently chlorophyll meter (SPAD) readings. It has also been shown that increasing nutrient solution strength (NSS) increases tomato productivity, but there are no reports regarding how NSS affects SPAD readings under greenhouse conditions. Genotype may also influence SPAD readings, and standardization for cultivar and sampling time may be needed. The objective of this study was to characterize SPAD readings for five tomato cultivars, and SPAD reading response to a combination of two nutrient solutions strength (NSS) (1X and 4X Steiner solution strength daily applied 18 days after transplanting at 7 p.m.) and two concentrations of NH₄–N in solution (0 and 25%) in order to evaluate the potential of SPAD readings as a tomato yield predictor in greenhouse production systems. The SPAD readings were not uniform across tomato varieties tested, being consistently higher for “Max” and lower for the other varieties. Initially, SPAD readings for tomato varieties used in this study were low at the vegetative stage, and increased up to 40 days after transplant (DAT), but subsequently decreased at 49 DAT, or the fruit set of the first and second clusters. After this time, SPAD readings showed no variation. Chlorophyll meter readings for Max were higher in the top plant layers, but decreased in the top plant layer of the other tomato varieties. The SPAD readings were higher for plants supplied with 25% NH₄–N than those without NH₄–N in solution, but the use of a nighttime nutrient solution did not affect SPAD readings. None of the possible interactions among tomato variety, NH₄–N:NO₃–N ratio, and NSS were consistently significant. SAPD readings may be useful in monitoring low or high supply of N in greenhouse grown tomato plants.     

应用叶绿素计诊断烤烟氮素营养状况

为探讨叶绿素计在估测烤烟叶绿素和氮浓度上的应用价值,进行了3个田间试验。即:郑州点2003年设施N.51.0.kg/hm2与4个品种NC89、RG17、85048、541;2004年设5个氮肥用量:N.30.04、0.5、51.0、61.5、75.0.kg/hm2与2个品种中烟101、云烟85;玉溪点于2005年设5个氮肥用量:N.02、7.0、54.5、81.8、109.0.kg/hm2与K326品种的试验。测定了不同试验条件下烤烟叶片的叶绿素计(SPAD-502和CCM-200)值和实际叶绿素浓度、全氮浓度,并进行了三者关系分析。结果表明,应用叶绿素计监测烤烟叶片最佳测定部位为完全展开叶的中部。叶绿素计测定值因年份、地点、氮肥水平、叶位、同一叶片不同的部位而异。叶绿素计值与叶绿素浓度、叶片全氮浓度之间有稳定的极显著相关性。叶绿素计SPAD-502的SPAD值和CCM-200的CCI值与叶绿素浓度之间的决定系数分别为0.8755(P0.001)和0.9499(P0.001)。SPAD计值(SPAD)与全氮浓度(N)之间回归方程为N=0.0265SPAD+0.9601(R2=0.7649,P0.001),经检验该模型具有较好的精确性和普适性,利用叶绿素计进行烤烟氮素营养监测是可行的。     

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.     

Chlorophyll meter readings in corn as affected by plant spacing

Abstract

Heightened environmental consciousness has increased the perceived need to improve nitrogen (N) use efficiency by crops. Synchronizing fertilizer N availability with maximum crop N uptake has been proposed as a way to improve N‐use efficiency and protect ground water quality. Chlorophyll meters (Minolta SPAD 502) have the potential to conveniently evaluate the N status of corn (Zea mays L.) and help improve N management. A potential problem with the use of chlorophyll meters is the effect of within‐row plant spacing on meter reading variability. Chlorophyll meter readings and leaf N concentration of irrigated corn at anthesis and grain yield at harvest were measured on plants grouped into eight within‐row plant spacing categories. Leaf N concentration was not affected by plant spacings, but chlorophyll meter readings and grain yield per plant increased as plant competition decreased and N fertilizer rate increased. These data indicate that avoiding plants having extreme spacings can greatly increase precision when using chlorophyll meters to evaluate the N status of corn.     

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.     

Elevated atmospheric carbon dioxide effects on sorghum and soybean nutrient status 1

Increasing atmospheric carbon dioxide (CO₂) concentration could have significant implications on technologies for managing plant nutrition to sustain crop productivity in the future. Soybean (Glycine max [L.] Merr.) (C3 species) and grain sorghum (Sorghum bicolor [L.] Moench) (C4 species) were grown in a replicated split‐plot design using open‐top field chambers under ambient (357 μmol/mol) and elevated (705 μmol/mol) atmospheric CO₂. At anthesis, leaf disks were taken from upper mature leaves of soybean and from the third leaf below the head of sorghum for analysis of plant nutrients. Leaf greenness was measured with a Minolta SPAD‐502 chlorophyll meter. Concentrations of chlorophylls a and b and specific leaf weight were also measured. Above‐ground dry matter and seed yield were determined at maturiry. Seed yield of sorghum increased 17.5% and soybean seed yield increased 34.7% with elevated CO₂. There were no differences in extractable chlorophyll concentration or chlorophyll meter readings due to CO₂ treatment, but meter readings were reduced 6% when sorghum was grown in chambers as compared in the open. Leaf nitrogen (N) concentration of soybean decreased from 54.5 to 39.1 g/kg at the higher CO₂ concentration. Neither the chambers nor CO₂ had an effect on concentrations of other plant nutrients in either species. Further work under field conditions is needed to determine if current critical values for tissue N in crops, especially C3 crops, should be adjusted for future increases in atmospheric CO₂ concentration.     

Use of a chlorophyll meter to evaluate the nitrogen status of dryland winter wheat

Abstract

Chlorophyll meter leaf readings were compared to grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N levels from N rate studies for dryland winter wheat Soil N tests and wheat leaf N concentrations have been taken in the spring at the late tillering stage (Feekes 5) to document a crop N deficiency and to make fertilizer N recommendations. The chlorophyll meter offers another possible technique to estimate crop N status and determine the need for additional N fertilizer. Results with the chlorophyll meter indicate a positive association between chlorophyll meter readings and grain yield, leaf N concentration and soil NH₄‐N plus NO₃‐N. Additional tests are needed to evaluate other factors such as differences among locations, cultivars, soil moisture and profile N status.     

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.     

Use of a hand‐held chlorophyll meter in winter wheat: Evaluation of different measuring positions on the leaves

A portable chlorophyll meter (Minolta SPAD‐502) was used to assess the nitrogen status of winter wheat (Triticum aestivum L.) in two fertilizer trials at Apelsvoll Research Centre, located in south‐east Norway. The midpoint of the last fully developed leaf was found to be the best position on the winter wheat plant on which to take chlorophyll meter readings. This conclusion was reached after examination of the relationships between soil‐plant analyses development (SPAD) readings taken at different positions on the plant and leaf nitrogen concentration, grain yield and grain protein content. Emphasis was also laid on finding a measuring position that was convenient from a practical point of view. The relationships between chlorophyll meter readings and the parameters investigated were better at Zadoks growth stage (GS) 49 than earlier in the season at GS 31.     

Optimizing the Nitrogen Management Strategy for Winter Wheat in the North China Plain Using Rapid Soil and Plant Nitrogen Measurements

Excessive nitrogen (N) fertilizer with improper split-application in small-scale farming is widespread for reducing N use efficiency and polluting the environment. The objective of this study was to develop a strategy for providing winter wheat with twice-topdressing N by quickly measuring the soil and plant N status. During the period 2009–2011, a field experiment was conducted for winter wheat cultivar Zhongmai-175 in the North China Plain. The mineral N (Nmin) pool at a soil depth of 0–90 cm and topdressing N twice, as total N supply, was gradually increased from 0 to 420 kg N ha^–1 to mimic the farmers´ practices. Measurements with the Soil Plant Analysis Development (SPAD) meter were taken on the uppermost fully expanded leaf, and the SPAD index was expressed relative to SPAD readings of sufficiently fertilized plants. Grain yield exhibited linear-plus-plateau responses to total N supply with a significant difference between years, the r² ranged from 0.73 to 0.94. With a basal N application of 30 kg ha^–1, the soil Nmin at 0–90 cm supplemented by twice-topdressing N (1:1 ratio) at Zadoks growth stage (ZGS) 22–23 in early spring and ZGS 47–52 was required at 150–165 kg N ha^–1 to achieve a maximum grain yield of 3.9–5.3 t ha^–1. The SPAD index exhibited a strong exponential response to N supply irrespective of plant growth stage and year (r² = 0.95–0.97); the value of 0.94 was critical in denoting N deficiency from sufficiency status. The N topdressing at ZGS 47–52 could be precisely modified/estimated by the equation y = 161.7–218x^5.16, where x is the SPAD index. Since SPAD readings varied significantly from year to year, our study suggests that it might be difficult to precisely manage field N for winter wheat.