SPAD Measurements Research Articles

EFFECT OF NITROGEN FERTILIZER RATES ON YIELD, YIELD COMPONENETS AND GRAIN QUALITY MEASUREMENTS OF SOME WHEAT CULTIVARS USING SPAD-METER

Two field experiments were carried out at Agric. Res. Station, Agric. Res. Centre, Giza Governorate, Egypt during 2006/2007 and 2007/2008 growing seasons. The aim of this study was to find the relationships between fertilization rates and SPAD readings and economic N application to minimize pollution and cost, and maximize wheat growth and yield. Three bread wheat genotypes namely Sakha 94, Giza 168 and Gemmiza 9 and five N fertilization treatments, i.e., 0, 40, 80 kg N/fad (as a recommended N rate) and 120 kg N/fad as high rate as well as N applied according to SPAD measurements, nitrogen sufficiency indices (NSI). The results showed gradual remarkable increase in SPAD values versus advancing wheat plant towards maturity till reached their maximum values at early grain filling stage, i.e., 118 days from planting. On the other hand, the relationship between SPAD readings and N rates indicated that wheat plants received either 80 kg N/fad or N fertilizer according to NSI had statistically the same values of yield and its components with insignificant discrepancy between them. The results clearly indicated that the studied characters were significantly affected by increasing N fertilizer rates except for harvest index. The increment of grain and biological yields via N fertilization rates was accompanied with rising crude protein yield. The results indicated significant increases in crude protein, wet and dry gluten versus increasing N fertilizer rates till reached their maximal values at a level of 80 kg N/fad or according to NSI. A positive relationship between grain protein content and both wet and dry gluten was found. The rate of increase in wet gluten was lower than that of dry gluten, therefore, the hydration value was significantly decreased. In conclusion, the use of SPAD meter and NSI was very important to detect the nitrogen physiological rate for growth, yield and grain quality of wheat plant. Moreover, the use of NSI economized the cost of nitrogen fertilizer by rate of about 25% and more reliable for production of wheat without effect on wheat yield.

Effect of Abiotic Stresses on the Nondestructive Estimation of Rice Leaf Nitrogen Concentration

Decision support tools for non-destructive estimation of rice crop nitrogen (N) status (e.g., chlorophyll meter [SPAD] or leaf color chart [LCC]) are an established technology for improved N management in irrigated systems, but their value in rainfed environments with frequent abiotic stresses remains untested. Therefore, we studied the effect of drought, salinity, phosphorus (P) deficiency, and sulfur (S) deficiency on leaf N estimates derived from SPAD and LCC measurements in a greenhouse experiment. Linear relations between chlorophyll concentration and leaf N concentration based on dry weight (Ndw) between SPAD values adjusted for leaf thickness andNdwand between LCC scores adjusted for leaf thickness andNdwcould be confirmed for all treatments and varieties used. Leaf spectral reflectance measurements did not show a stress-dependent change in the reflectance pattern, indicating that no specific element of the photosynthetic complex was affected by the stresses and at the stress level applied. We concluded that SPAD and LCC are potentially useful tools for improved N management in moderately unfavorable rice environments. However, calibration for the most common rice varieties in the target region is recommended to increase the precision of the leaf N estimates.

Using a Chlorophyll Meter to Evaluate the Nitrogen Leaf Content in Flue-Cured Tobacco (Nicotiana tabacum L.)

In flue-cured tobacco N fertilizer is commonly applied during pre-planting, and very often applied again later as a growth-starter. It is generally held that the efficiency of N-fertilizer use can be improved by evaluating the leaf Nstatus after transplanting and until flowering stage. N use efficiency in this context does not refer merely to the yield but also to the quality, in the meanwhile minimizing the negative effects on the environment. To investigate these aspects, we evaluated the capacity of a Minolta model SPAD-502 chlorophyll meter to estimate the N-status in flue-cured tobacco. The aims was to verify if a relationship exists between SPAD readings and leaf N content, and if a single leaf, in a well defined stalk position, could represent the nitrogen content of the whole plant. During the years 1995 and 1996, a pot experiment was conducted using two flue-cured tobacco varieties. SPAD values, total chlorophyll, total N contents and leaf area were measured throughout the growing season, on each odd leaf stalk position. SPAD values were well-correlated with both total chlorophyll and total N leaf concentration, and the regression coefficients were higher when relationships were calculated on a leaf-area basis. For both relationships, SPAD-total chlorophyll and SPAD-total N, the best fittings were obtained with quadratic equations. One leaf stalk position alone is able to monitor the N-status of the whole plant during the first six weeks after transplanting, without distinction of year and variety effects. The SPAD measurement of one leaf per plant, throughout the vegetative growing season, is therefore a valid tool to test the N-status of the crop in a period when a required N supply is still effective.

GENETIC ANALYSIS OF IRON CHLOROSIS TOLERANCE IN MYROBALAN PLUM X ALMOND-PEACH HYBRIDS

Iron deficiency is responsible for enormous economical losses in a wide range of crops in the Mediterranean area. Different species vary in their susceptibility from poorly to severely affected leaf chlorosis, one of the main common symptoms for the iron deficiency. The prevention of this nutritional disorder involves the use of tolerant rootstocks as the best alternative to palliate the problem in fruit tree plantations. The genetic control of the tolerance to this abiotic stress in trees is still unknown but studies in other crops suggested that it could be a quantitative trait. For that, this work is directed to understand the genetic control of iron chlorosis in tree fruits. Two approaches are being used: the quantitative genetics with detection of QTLs related with iron chlorosis and the molecular genetic approach with the search of candidates genes differentially expressed under iron deficiency. A F1 population derived from a three ways interspecific cross between the myrobalan (P. cerasifera): ‘P.2175’ and the almond x peach hybrid (P. dulcis x P. persica): Felinem (formerly GxN 22) was analyzed. SPAD measurements were performed in the leaves of the F1 individuals detecting segregation to iron chlorosis tolerance. Preliminary results showed correlation between the chlorophyll content and genomic regions located in chromosomes 2 and 6, close to other reported QTLs involved in fruit quality and fungus resistance. The candidate genes approach is being implemented based on in silico screening of genes shown to be expressed in response to iron deficiency in roots, such as those encoding FRO2, IRT1 and other candidate genes differentially expressed in grape rootstocks under iron induced chlorosis.

New method to assess barley nitrogen nutrition status based on image colour analysis: Comparison with SPAD-502

Measuring the nitrogen nutrition status of plants is useful for nitrogen fertiliser management. As nitrogen is one of the main structural components of chlorophyll, its nutrition status is highly correlated with the greenness of leaves. This paper proposes and evaluates a new low-cost method to estimate the N-nutrition status of plants using digital colour image analysis. A method has been developed in which principal component analysis is applied to digital images to calculate a greenness index using RGB components of the colour image, which yields an estimate of the amount of N in the plant. To evaluate its quality, we calculated the correlation between the index and measurements obtained with a SPAD-502 chlorophyll meter, normally used in decision-making in fertiliser management. The performance of the proposed index is better than that of others previously investigated. Furthermore, the capacity of our index to predict N deficiencies affecting barley yield was equal to or better than that of SPAD measurements under our experimental conditions.

Prognosis and correction of iron chlorosis in peach trees and relationship between iron concentration and Brown Rot

This study investigates the possible correlations between bark, floral, and leaf iron (Fe) concentrations and SPAD measures to be used as early methods for prognosis of iron chlorosis in peach trees. The results showed that there were significant correlations between bark, floral and leaf Fe concentrations and SPAD measurements. This study shows for the first time the possibility of using bark analysis as an early predictive method of iron chlorosis in peach trees. Differences in mineral composition of leaves of peach trees, in relation to rootstocks were also found. This study also investigated the distribution of mineral elements in different parts of peach leaves. Tissue analysis of different leaf parts showed that the peripheral and petiole of leaves had the highest P, Ca, Mg, Zn, Fe, B and Cu concentrations. In contrast, the highest K concentration was found in the internal parts of leaves. High Mn concentration was found in the laminar of leaves, but was lower in the petioles. In other experiments, the effect of different sources of Fe application on the leaf Fe concentrations and development of Brown Rot in the year of application and one and 2 years later was also examined. No application increased significantly the leaf Fe concentrations in the year of application and 1 year later. Leaf Fe concentrations were significant higher in trees treated with FeSO 4·7H 2O + S 2 years after application. The possible effect of flesh Fe concentration to susceptibility of peach (cv. Sun Crest) to Monilinia laxa was also evaluated. The results showed no correlation between flesh Fe concentration and susceptibility of peach to M. laxa. Besides, no statistical difference was found in the susceptibility of peach to M. laxa collected from the cultivar Sun Crest grafted on different rootstocks.

小麦の子実タンパク含有率の評価における出穂-開花期のSPAD計測，地上及び航空機ハイパースペクトル計測の比較

小麦の子実タンパク含有率の評価における出穂-開花期のSPAD計測，地上及び航空機ハイパースペクトル計測の比較

Shoot biomass growth is related to the vertical leaf nitrogen gradient in Salix canopies

Plant canopy optimization models predict that leaf nitrogen (N) distribution in the canopy will parallel the vertical light gradient, and numerous studies with many species have confirmed this prediction. Further, it is predicted that for a given canopy leaf area, a low vertical light extinction coefficient will promote rapid growth. Therefore, the ideal canopy of fast-growing plants should combine high leaf area index with a low light extinction coefficient; the latter being reflected in a flat vertical leaf N gradient throughout the canopy. Based on data from an experimental Salix stand (six varieties) grown on agricultural land in central Sweden, we tested the hypothesis that shoot growth is correlated with vertical leaf N gradient in canopies of hybrid willows bred for biomass production, which could have implications for Salix breeding. Tree improvement research requires screening of growth-related traits in large numbers of plants, but assessment of canopy leaf N gradients by chemical analysis is expensive, time-consuming and destructive. An alternative to analytical methods is to estimate leaf N gradients nondestructively with an optical chlorophyll meter (SPAD method). Here we provide a specific calibration for interpreting SPAD data measured in hybrid willows grown in biomass plantations on fertile agricultural land. Based on SPAD measurements, a significant and inverse relationship (r(2) = 0.88) was found between shoot biomass growth and vertical leaf N gradient across canopies of six Salix varieties.

Effects of different sources of iron, hormones and Agrobacterium tumefaciens on the chlorophyll and iron concentration in the leaves of peach trees

The aim of this study was to investigate the effect of different sources of iron, hormones and Agrobacterium tumefaciens in the chlorophyll and iron concentration of the peach cultivars Katerina and Fire Blight. The results showed that the concentration of Fe in the leaves was significantly increased after spraying with FeSO<sub>4</sub>.7H<sub>2</sub>O (alone or in combination with KNO<sub>3</sub>, urea, citric acid or ascorbic acid) or with GA<sub>3</sub> + Kinetin. Soil applications with Fe-EDDHA also significantly increased the iron concentration in leaves. Chlorophyll (a/b) increased only in trees sprayed with citric acid or H<sub>2</sub>SO<sub>4</sub> 60 days after application. SPAD chlorophyll measurements showed that Fe-EDDHA and FeSO<sub>4</sub>.7H<sub>2</sub>O + organic matter, applied as soil drench, significantly increased the chlorophyll concentration in leaves of Katerina even up to 120 days after application. Foliar treatments had no significant effect on the SPAD index. SPAD measurements also showed that the concentrations of chlorophyll in leaves of the rootstocks St. Julien 655/2 and wild seedling rootstocks were significantly lower than in GF677 and Antafuel. The rootstocks inoculated with the A. tumefaciens strain Ag-28 alone showed a significantly lower chlorophyll concentration than the uninoculated ones.

Foliar Iron Fertilization of Peach (Prunus persica (L.) Batsch): Effects of Iron Compounds, Surfactants and Other Adjuvants

Experiments to assess the capability of different combinations of iron (Fe) compounds and adjuvants to provide Fe via foliar application to Fe-deficient plants have been carried out. A total of 80 formulations containing (1) one of five Fe-compounds [FeSO4·7H2O, Fe(III)-citrate, Fe(III)-Ethylenediaminetetraacetic acid (EDTA), Fe(III)-Diethylenetriamine pentaacetic acid (DTPA), Fe(III)-Iminodisuccinic acid (IDHA)], (2) a surfactant (Mistol, alkyl-polyglucoside1 or alkyl-polyglucoside2), and (3) an adjuvant (glycerol, methanol or glycine–betaine) were studied with respect to leaf wetting ability and surface tension. From the initial formulations only 26 resulted in adequate leaf wetting, 20 with alkyl-polyglucoside2 and 3 each with Mistol and alkyl-polyglucoside1, and some of them (four with alkyl-polyglucoside2, one with Mistol, and three with alkyl-polyglucoside1) were found to have inadequate surface tension values for use as foliar fertilizers. In a second experiment, 20 formulations containing alkyl-polyglucoside2 and one each of the five Fe-compounds and adjuvants listed above, were used for a foliar experiment with Fe-deficient peach trees [Prunus persica (L.) Batsch] grown under field conditions. Iron-deficient shoots were sprayed only once and leaf re-greening was assessed over 6 weeks for leaf chlorophyll content (via SPAD measurements) and percentage of green leaf area (via image analysis). Foliar Fe application always resulted in leaf Chl increases, although different degrees of re-greening were observed for the various Fe-compounds tested. Best results were obtained after treatment with formulations containing (in a decreasing order): Fe(II)-sulfate, Fe(III)-citrate, Fe(III)-EDTA, Fe(III)-IDHA, and Fe(III)-DTPA. A positive effect of adding glycerol, methanol or glycine–betaine was often observed, although the effect depended on each Fe-containing compound, indicating the existence of significant interactions between spray components. Results are of importance while trying to critically evaluate the potential of Fe sprays as a viable strategy to remedy plant Fe deficiency under field conditions.

Can Leaf Chlorophyll Measures at Differing Growth Stages be used as an Indicator of Winter Wheat and Spring Barley Nitrogen Requirements in Eastern Canada?

AbstractPlant need‐based N management approaches may increase the efficiency of N fertilizer application in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). The leaf chlorophyll concentration estimated through the SPAD‐502 meter gives a relative assessment of N status in crop. Field trials were conducted near St John's, Newfoundland, between 1997 and 2000 to describe the relationship between winter wheat and spring barley grain yield, protein content, protein yield and SPAD measurements, as affected by differential stage of crop growth, seeding rate and topdress N fertilizer. Grain yield, protein content, and protein yield of winter wheat and spring barley exhibited linear responses to increasing N topdress application rate. SPAD‐502 values were moderately to highly positively correlated with grain yield, protein content, and protein yield as a result of increasing topdress N fertilization, and moderately negatively correlated as a result of increasing seeding rate. It may be difficult to make an N‐application rate recommendation based on SPAD measurements, as a critical SPAD value may vary among years, locations, cultivars and soil characters.

Relationship between Contents of Chlorophyll (a+b) (SPAD values) and Nitrogen of Some Temperate Grasses

In a field experiment the chlorophyll (a+b) (SPAD readings) and nitrogen contents of three grass species (Festuca arundinacea Schreb., Lolium perenne L., and Lolium multiflorum Lam.) and three intergeneric hybrids of Festuca pratensis Huds. × Lolium multiflorum Lam. and Festuca arundinacea Schreb. × Lolium multiflorum Lam. were measured. Close relationships were found between SPAD readings and nitrogen leaf content (r 2 = 0.873** 0.491** and 0.938**) for the 1st, 2nd, and 3rd cut, respectively. SPAD readings and N contents were closely correlated (r = 0.836**) confirming that SPAD measurements could be used in grass selection and/or breeding for high N concentration in herbage.

Impact of Water Treatment on Foliar Damage of Landscape Trees Sprinkle Irrigated with Reuse Water

Abstract An experiment was conducted on four container-grown tree species placed under five different irrigation reuse water treatments to determine the extent of foliar damage after a 14.5-month period. The tree species included Heritage oak (Quercus virginiana Mill. ‘Heritage’), desert willow (Chilopsis linearis (Cav.)/Sweet), flowering plum (Prunus cerasifera Ehrh ‘Atropurpurea’), and Chinese pistache (Pistacia chinensis Bunge). Plant response and an index of visual damage (IVD) were assessed at different times throughout the experiment. Ion concentrations in the leaf tissue were different for species (S) (p < 0.001), treatment (T) (Na, K, SO4, p < 0.05) and by a species by treatment interaction (S × T) (Na, Ca, Mg, K and SO4, p < 0.05). SPAD measurements varied by S (p < 0.001), T (p < 0.001) and by an S × T interaction (p < 0.045). SPAD measurements decreased as the leaf tissue Na concentration increased (SPAD = 47.49 – 12.46(Na), r2 = 0.38, p < 0.01). The IVD varied by S (p < 0.001), T (p < 0.001) and by an S × T interaction (p < 0.001). Na, Ca and SO4 tissue ion concentrations could account for 52% of the variability in the IVD (IVD =−1.93 + 4.63(Na) + 2.60(Ca)−0.001(SO4), p < 0.01). Because the irrigation treatment resulting in the lowest IVD was species dependent, irrigation treatment selection should be based upon an evaluation of the landscape species composition and the potential cost of implementing a given strategy. The response observed in this study suggests that a single universal irrigation strategy does not exist, indicating that emphasis must be placed on initial and replacement plant selection.

EVALUATION OF CHLOROPHYLL METER TO ASSESS NITROGEN STATUS OF COCKSFOOT SWARD

The sward nitrogen index (NNI), computed from nitrogen (N) content and standing herbage mass, is a sound approach to assess the N sward status for tactical adjustment of N fertilizer. However, chlorophyll meter (SPAD) readings might simplify the procedure, avoiding having to weigh and analyze the herbage. Four experiments, combining two rates of N additions and two cutting regimes, were carried out on a cocksfoot (Dactylis glomerata L. cv. Lude) sward in order to investigate the relationship between SPAD readings and NNI. For two of them, SPAD readings were taken at the mid-point of the youngest mature lamina. For the two others, they were taken at the mid-point of laminae, which composed the upper sward layer (from four to 14 cm at the top of the canopy). There was a satisfactory relationship (P < 0.001) between plant N content and SPAD measurements, whatever the sampling procedure. Furthermore, we found a close relationship between SPAD readings and NNI calculations for both methods of SPAD measurements, but the parameters were significantly different for the two methods, in agreement with the relationships established for N content in the uppermost sward layer and the youngest fully expanded lamina. Suggestions are made to improve the sampling procedure by taking into account the vertical gradient in N content at the sward and lamina levels.

Iron chlorosis in olive in relation to soil properties

Chlorosis due to iron (Fe) deficiency is becoming severe in olive (Olea europaea L.) trees growing on some highly calcareous soils in southern Spain. We investigated the relationships between the incidence of Fe chlorosis in three olive varieties (‘Hojiblanco’, ‘Manzanillo’ and ‘Picual’) and soil properties. Leaf chlorophyll content, estimated by the mean value of three SPAD measurements during the growing season, was poorly correlated with soil carbonate content and reactivity. In contrast, it was significantly correlated with the clay content and with the amounts of Fe extracted with oxalate (Feox), citrate/ascorbate (Feca), and diethylendiaminepentaacetid acid (FeDTPA). This suggests that the content and reactivity of poorly crystalline Fe compounds play an important role in Fe nutrition. The three olive varieties did not differ significantly in their susceptibility to Fe chlorosis. Soil test critical levels separating chlorotic and non-chlorotic trees were 300 g clay kg −1 soil and 0.35 g Feox kg −1 soil.

Measuring Wheat Senescence with a Digital Camera

Documenting crop senescence rates is often difficult because of the need for frequent sampling during periods of rapid change and the subjective nature of human visual observations. The purpose of this study was to determine the feasibility of using images produced by a digital camera to measure the senescence rate of wheat and to compare the results with changes in greenness determined by two established methods. Measurements were made as part of an experiment to determine the effects of elevated CO 2 and limited soil nitrogen on spring wheat (Triticum aestivum L.) at the University of Arizona's Maricopa Agricultural Center, near Phoenix, AZ. Greenness' measurements were made during senescence of the crop with a color digital camera, a hand-held radiometer, and a SPAD chlorophyll meter. The green to red (G/R) for each pixel in an image was calculated and the average G/R computed for cropped images from a digital camera representing 1 m 2 for each treatment and sample date. The normalized difference vegetation index (NDVI) was calculated from the red and near-infrared canopy reflectances measured with a hand held radiometer. A SPAD reading was obtained from randomly selected flag leaves. All three methods of measuring plant greenness showed similar temporal trends. The relationships between G/R with NDVI and SPAD were linear over most of the range of G/R. However, NDVI was more sensitive at low values than G/R. G/R was more sensitive above G/R values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while G/R responded to both chlorophyll concentration in the leaves as well as the number of leaves present. Color digital imaging appears useful for quantifying the senescence of crop canopies. The cost of color digital cameras is expected to decrease and the quality and convenience of use to improve.

Effect of Leaf Phosphorus and Potassium Concentration on Chlorophyll Meter Reading in Rice

Chlorophyll meter (SPAD) is a convenient tool to estimate leaf nitrogen (N) concentration of rice plants. There is no information on the effects of leaf phosphorus (P) and potassium (K) concentration on SPAD readings and on the relationship between SPAD values and leaf N concentration in the literature. In 1996 dry season, cv IR72 was grown at the International Rice Research Institute (IRRI) and the Philippine Rice Research Institute (PhilRice) under various N, P and K fertilizer combinations. SPAD measurements were made on the topmost fully expanded leaves at mid-tillering and panicle initiation. The leaves were then detached, dried and analyzed for N, P and K. The SPAD values were highly correlated with leaf N concentration (r = 0.93 to 0.96). Fertilizer-K application did not affect SPAD values, leaf N concentration, or the relationship between the two. Phosphorus deficiency reduced leaf N concentration at mid-tillering, but increased leaf N concentration at panicle initiation when the same amount of N was applied. The SPAD values were 1 to 2 units greater for zero-P plants than P-treated plants at a given leaf N concentration at mid-tillering. At panicle initiation, the relationship between SPAD values and leaf N concentration was not significantly affected by leaf P status. These results suggest that a different regression equation between SPAD values and leaf N concentration should be used to estimate leaf N concentration of P-deficient and P-sufficient rice leaves at vegetative stage using a SPAD.

Non‐destructive Determination of Leaf Chlorophyll Content in Four Crop Species1

AbstractA recent non‐destructive technique allows estimation of leaf chlorophyll content using the portable SPAD‐502 chlorophyll meter. Measurements were taken on four species (winter wheat, maize, soyabean and tobacco) subjected to different nitrogen regimes or senescence status and the: non‐destructive readings were compared with analytical results obtained by solvent extraction. In general, the relationship between the SPAD measurement and the analytical result was not linear and species was a factor in three out of four crops. Linear, quadratic and exponential curve fitting are presented; only die interpolation with a polynomial exponential function adequately descries the whole data set. The presence of statistically non‐significant differences between the estimated values of wheat and maize on the one hand and significant: points of difference between those of tobacco and soyabean on the other suggests distinct behaviour patterns far monocots and cicots. This type of response maybe explained by differences, in the optical properties of pigments with differing sparial distributions (sieve effect) and therefore by in vivo and in vitro different procedures and the structural diversity of leaves belonging to the two subclasses.

Association of specific leaf weight, an estimate of chlorophyll, and chlorophyll concentration with apparent photosynthesis in soybean

Increasing specific leaf weight (SLW) may improve leaf apparent photosynthesis (AP) in soybean [Glycine max (L.) Merr.] but screening for SLW and AP is laborious. The Objectives of this study were (i) to determine the time course of SLW and chlorophyll concentration in experimental lines selected for differences in SLW and (ii) to evaluate the potential use of the Minolta 502 SPAD meter as a rapid estimator of SLW, AP and chlorophyll concentration in leaves of soybean. In 1991 and 1992, sixteen experimental lines representing extremes in SLW were grown at Urbana, IL, and West Lafayette, IN, with three replications at each location. SPAD values, SLW and AP were measured at the R2 (full flower), R4 (full pod) and R5 (beginning seed) growth stages. In 1992 SLW, SPAD values and chlorophyll concentration were measured weekly. Seasonal patterns of SPAD values, SLW, and chlorophyll concentration were very similar through R5. After R5, SLW continued to increase but SPAD values and chlorophyll concentration declined. SPAD values and SLW were highly correlated at the R2, R4 and R5 stages at both locations and in both years. Environmental conditions during this research were not suitable for maximum AP expression, which is likely why AP and SPAD values were correlated only at the R4 growth stage at Urbana in 1992. SPAD measurements were consistent across diverse environments and effectively separated the high SLW lines from the low SLW lines. Measuring with the Minolta 502 SPAD meter is rapid, simple and non-destructive and could be an alternative method for direct selection for SLW.