Yes , the SPAD value of flag leaves is affected by the level of nutrient management, especially with respect to nitrogen nutrition...

Yes, the SPAD values are affected by the quality and how nutrients are added.

Definitely yes! The nutrition status must be reflected on the source that flag leaf represents its major component, this in turn will affect the sink (Yield and its components).

Generally the first fully open leaf from the top best reflects the supply of N to the plants at any time during the growth of the crop plants. Of course SPAD values of the flag leaves is influenced by fertilizer management. The question is not very clear as to what is the purpose of measuring SPAD readings of flag leaves of which crop.

SPAD Values and Nitrogen Nutrition Index for the Evaluation of

Rice Nitrogen Status( Plant Prod. Sci. 17(1): 81―92 (2014) )

Abstract: Plant-based diagnosis is one of the most important methods to determine nitrogen (N) content of crops. Our objective was to establish the relationship between soil-plant analysis development (SPAD) values and N nutrition index (NNI) during the three developmental stages of rice and apply the SPAD meter as diagnostic tools for predicting grain yield response to N fertilization. We determined the SPAD values of four uppermost fully expanded leaves of two rice cultivars at six N fertilization levels at three growth stages and examined the relationship between SPAD values and NNI. The critical N concentration (Nc) was 5.31 W–0.5 in Xiushui63, and 5.38 W–0.49 in Hang43, where W is the total shoot biomass. The correlation between SPAD value and NNI varied with the leaf position, developmental stage, and variety. The lower leaf appeared to be more sensitive to the N level than the upper leaf in the response of biomass, and could be more suitable as a test sample for N status diagnosis, especially in the booting and heading stage. The dependence of grain yield on SPAD values of the fourth fully expanded leaf (L4) was significant at booting stage (R2 L4 = 0.82** in 2011, R2 L4 = 0.72** in 2012). Ratio of SPAD values of L4 to that in the N-saturated plot (RSPAD) (R2 L4 = 0.92** in 2011, R2 L4 = 0.77** in 2012) and NNI (R2 = 0.96** in 2011, R2 = 0.86** in 2012) at booting stage demonstrated a closer relationship with grain yield. PDF enclosed for further reference...

Sure, the SPAD value or chlorophyll content, flag leaf weight, flag leaf area and nutrients uptake in rice flag leaves are significantly increase by the increasing in the level of nutrients management. Flag leaf is the best indicator for good nutrients uptake, panicles health and grain yield. I did study it in my Ms.c and Ph.D theses....

Thesis EFFECT OF BIO AND MINERAL NITROGEN FERTILIZER ON GROWTH, YIE...

Thesis RESPONSE OF RICE YIELD TO APPLICATION OF NITROGEN FROM DIFFE...

Yes , definitely it is indicator of Nitrogen status through greenness of leaf

Yes, SPAD values of flag leaves are affected by N management in cereals. Even, leaf color does affect SPAD values where deep green flag leaves showed significantly different SPAD values from light green flag leaves in barely .

Will application of magnesium and iron through soil or especially through foliar application influence/ interfere with the chrophyll content in leaf and consequently the measured SPAD values? If so,how that affects the N recommendation to cereal crop?

I agree with most of the answers. However, it's not only N that affects SPAD reading but also leaf age, leaf thickness, and the position of the leaf. As leaf ages, the rate of decrease of SPAD value increased. But this rate is slowed down with N application. The upper leaf (e.g. flag leaf) has higher SPAD value than lower leaf, and when N is applied the difference becomes higher. Application of N at the flowering stage may prolong duration of greenness or senescence (stay-green) and thus increases SPAD value.

SPAD readings are influenced by everything influencing the degree of "greenness" of a leaf, e.g., N, S, Mg, Fe and other factors like crop variety, draught and whatever else.

Making N recommendations based on SPAD readings can be made only on a ceteris paribus base, i.e., having made sure that everything except N can is taken care of and not (or be fairly assumed not to) influence the expression of green. A calibration to whatever sophistication is always necessary!

I agree with most of the answers.

In my opinion, SPAD reading is an indication of nitrogen status of the rice plant, but it is not just limited to N status alone.

Yes, SPAD value of flag leaf is affected by nitrogen application. Though the symptom of N deficiency appear in older leaf, we should understand that, plant produce visible symptom only in case of severe deficiency. Whereas SPAD is used to identify the deficiency even before it start showing symptom i.e hidden hunger.

Though the impact of N deficiency was more in older leaf, it also have some effect flag leaf.

Yes all the answer are agreeable

Yes, I agree with most of the answers. However, since the SPAD reads the degree of greenness which is correlated to N content in the flag leaf. There should not be any other factor that affect the greenness of the leaf. example if there is iron deficiency or iron toxicity or disease such RYMV the SPAD reading will be affected regardless of N status in the soil.

YES it is true that the N content in the flag leaf has significant effect on the yield. This is to say, prolonged greenness of the flag leaf increase the rice yield significantly.

Yes, because an application of nitrogen in organic and inorganic form at right time enhances chlorophyll content which resulted to higher SPAD values. Nitrogen availability can affect photosynthetic rate per unit leaf area but often the main reason for the large effect of additional N on crop growth is that it increases leaf area per plant and consequently increases leaf area index. Moreover, The Soil Plant Analysis Development (SPAD) chlorophyll meter is one of the most commonly used diagnostic tools to measure crop nitrogen status. However, the measurement method of the meter could significantly affect the accuracy of the final estimation.

Yes, SPAD values of flag leaves can be significantly affected by differential fertilizer management. There is also a correlation between grain yield and different growth stages of the crop. Different fertilizer management practices can affect the amount of nutrients available to plants, which in turn can affect the SPAD values of the flag leaves. Additionally, different growth stages of the crop can affect the amount of photosynthesis taking place, which can also affect the SPAD values of the flag leaves.

Yes. With respect to flag leaves, which is the uppermost leaves on cereal crops like wheat and rice, nutrient management practices can influence their SPAD values. For example, providing appropriate nitrogen fertilization can enhance chlorophyll production and increase SPAD values in flag leaves. Insufficient nitrogen supply, on the other hand, may result in chlorosis (yellowing) of the leaves and lower SPAD values.

Enhancement in SPAD (27% and 30%) and normalized difference vegetation index (NDVI) (42% and 52%) values were observed with nitrogen (N) top dressing through SPAD-guided nutrient management, helped enhance crop growth indices, coupled with better dry matter partitioning and interception of sunlight. The utilization of a non-destructive SPAD-502 chlorophyll meter, which enables the measurement of nitrogen status in plant leaves, has gained popularity in agronomic crops. The SPAD chlorophyll meter readings and N content in leaves during different growth stages for assessment of crop N and prediction. SPAD readings are calculated based on two transmission values: the transmission of red light at 650 nm, which is absorbed by chlorophyll and the transmission of infrared light at 940 nm, at which no chlorophyll absorption occurs.