Multi-Channel Optoelectronic Measurement System for Soil Nutrients Analysis
, Shixin Li 1, Yatao Yang 1,2, Wei Zhang 1 and Jiandong Hu 1,2,*Round 1
Reviewer 1 Report
General comments
The manuscript is describing a portable 6-channel optoelectronic measurement system for the evaluation of the concentration of nitrogen (NH4+), phosphorus (P2O5) and potassium (K2O) in a solution obtained by chemical reaction of the soil sample with a commercial soil extractant solution.
The technical achievement is important and highly required by the farmers for dosing the amount of nutrients to be added to the soil in order to maximize their crops. This is recommending the paper publication after the revision, which is needed for improving the scientific level of the paper. Some specific comments and recommendations are shown below.
Specific comments and recommendations
Please describe the visible spectrum of light as being in the wavelength range of 380-740 nm. The range mentioned by you is already including the wavelengths from near infrared. Unfortunately this issue appeared also in other papers cited by you.
The statement saying that "phosphorus and potassium are not spectrally active in Vis/NIR range [22]" is confusing the reader and apparently suggesting that these chemical elements cannot be measured, which is not true. In the reference 22 which you are citing , it is mentioned that this is due to measurement of a solid sample of soil. Finally those authors have found that the two chemical elements are coupled with organic matter (OM). " The parameters P and K2O, which are not spectrally active in the Vis/NIR range should be better predicted when are highly correlated with OM".
A scientific background of your method based on liquid solution measurement should be presented. Actually the method itself is not new. I am attaching an old paper from 1942 showing how to identify phosphorus in a solution. Finally, some chemical reactions between the soil sample and soil extractant solution should be described proving the color formation in the final solution as a function of nutrient content in the soil. Thus the LED selection as a function of the solution color can be understood by the reader. Such correlation is not explicitly described in the text, but can be derived from the Table I.
In the row 234 there is something wrong ( absorbance of the solution of known concentration...of blank solution)
The equation (8) from row 245 seems to be wrong. The logarithm expression of As2 from equation (5) was not correctly introduced in equation (8).
The rational behind the equations for channel calibration should be explained so that reader to follow the thinking of the authors.
There are typing error which should be eliminated.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
Point 1:Please describe the visible spectrum of light as being in the wavelength range of 380-740 nm. The range mentioned by you is already including the wavelengths from near infrared. Unfortunately this issue appeared also in other papers cited by you.
Response 1: Thanks for the reviewer’s suggestions. Normally, the visible light range of the human eye is approximately 380-700 nm. However, a typical human eye can respond to wavelengths from about 380 to 740 nm, even 780nm depending on which source is used. Infrared waves are longer than those of visible light. Roughly, the wavelengths of infrared radiation (IR) range from about 700 nm to 1 mm. In terms of this description of visible light range, we have revised the sentences involving light range in this manuscript (Line 97, Page 3 in the revised manuscript).
Point 2:The statement saying that "phosphorus and potassium are not spectrally active in Vis/NIR range [22]" is confusing the reader and apparently suggesting that these chemical elements cannot be measured, which is not true. In the reference 22 which you are citing, it is mentioned that this is due to measurement of a solid sample of soil. Finally those authors have found that the two chemical elements are coupled with organic matter (OM). " The parameters P and K2O, which are not spectrally active in the Vis/NIR range should be better predicted when are highly correlated with OM".
Response 2: Thanks for the reviewer’s suggestions. In this literature [22], it said that the SVM regression model gave the best results for OM (R2 of 0.92) and Olsen P (R2 of 0.83). And these better predictions obtained for phosphorus content (Olsen) could be related to their higher correlations with OM. The lower prediction R2 values for K2O (R2 of 0.63 with LWR) might be explained the lack of spectral activity of this molecule.
Consequently, the original sentences “ Vis-NIR advanced spectroscopic measurement of soil total nitrogen developed using a diode array spectrophotometer with the wavelengths ranging from 399 nm to 1697 nm has been proved. However, phosphorus and potassium is not spectrally active in Vis/NIR range when the solid sample of soil is measured using spectral method [22]” have been replaced with “Vis-NIR advanced spectroscopic measurement of soil nutrition developed using a diode array spectrophotometer with the wavelengths ranging from 399 nm to 1697 nm has been proved. However, potassium is not spectrally active in Vis/NIR range when the solid sample of soil is measured using spectral method [22]” (Line 66-69, Page 2 in the revised manuscript).
Point 3:A scientific background of your method based on liquid solution measurement should be presented. Actually the method itself is not new. I am attaching an old paper from 1942 showing how to identify phosphorus in a solution. Finally, some chemical reactions between the soil sample and soil extractant solution should be described proving the color formation in the final solution as a function of nutrient content in the soil. Thus the LED selection as a function of the solution color can be understood by the reader. Such correlation is not explicitly described in the text, but can be derived from the Table I.
Response 3:The scientific background of this method based on liquid solution measurement was described in the Section of Measurement principle in the manuscript. The Beer-Lambert law was applied to take the absorbance of standard solutions, which is directly proportional to their concentrations. Chemical reactions between the soil sample and soil extractant solution are not complicated. However, the extractant is of great concern to the chemical reactions. In this manuscript, the novel universal extractant consisting of 0.45 M NaHCO3 and 0.374 M Na2SO4 was mentioned to provide the most useful indication for the rapid determination of available NPK content. Besides, the novelty of this manuscript compared to the previous literatures involving liquid solution measurement can be judged by the following points. (1) A multi-channel optoelectronic measurement system that is versatile enough to be exclusively developed as a field portable instrument for site soil nutrients analysis with low-cost design. (2) The optoelectronic measurement system with three-terminal adjustable shunt regulator for driving LED, the front-end circuit of an impedance amplifier for photodiodes, and the MCU circuit board including a chip of PIC24FJ64, a 16-bit A/D converter ADS1100, and a multiple switcher CD4051 was clearly described. (3) A novel universal extractant was utilized instead of the respective extractant for selective separation of NPK from other ions in soil solution (patented). (4) It is the first report on the detection of the NPK after absorbance compensations.
Point 4: In the row 234 there is something wrong (absorbance of the solution of known concentration...of blank solution)
Response 4: This original sentence has been replaced with “The average value of the absorbance of the standard solution of known concentration was calculated from 6 channels, accordingly.” (Line236-238, Page7 in the revised manuscript).
Point 5: The equation (8) from row 245 seems to be wrong. The logarithm expression of As2 from equation (5) was not correctly introduced in equation (8).
Response 5: The original equation (8) has been replaced with the following expression
(Line 246, Page 8 in the revised manuscript)
Point 6:The rational behind the equations for channel calibration should be explained so that reader to follow the thinking of the authors.
Response 6: In order to explain the rational behind the equations to readers, the following sentences have been added into the manuscript. “To ensure measurement accuracy of this multi-channel optoelectronic measurement system, the light intensity correction was performed prior to the absorbance compensation. Firstly, the transmitted light intensity of the blank solution is recorded. The correction factor of the light intensity of blank solution for each channel is initially calculated by the ratio of average value of the light intensity to the light intensity from each channel.” (Line 220-224, Page 6 in the revised manuscript)
Point 7: There are typing errors which should be eliminated.
Response 7: Thanks for the reviewer’s suggestions. The English of the manuscript has been thoroughly polished by Dr. Zephania Birech who is a Professor in the Department of Physics at University of Nairobi, Kenya.
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript presents a multichannel device that can detect NPK concentrations in soil sample solutions. The paper is well-organised and in good language although several minor grammatical errors exist. I suggest that the authors ask a native speaker to go over the manuscript again to correct them. I believe that the paper should be accepted for publication after some minor revisions.
Some specific comments:
The authors claim that this device is a rapid measurement system but at the same time the device requires a significant amount of sample preparation time and about 20 mins warm-up time. This claim is controversial since the user will need more than 1 hour to take measurements from soil samples. It is totally understood that 1 hour is clearly faster than the currently-used, lab-based methods and this a major advancement in the field. My suggestion is that the authors rephrase their manuscript to make this clear and eliminate any chances of misleading the reader.
Equations 1, 2 and 3 are very common in the field and they do not need to be explained in that detail. For example, equation 1 and 2 are essentially the same equation. The authors should try to make that section more concise since the background theory is very well understood in the community.
Almost all equations and symbols in the manuscript need to be rechecked since sometimes they appear as text and sometimes as symbols. The authors should use a consistent method of presenting equations and symbols in the manuscript based on the journal's requirements.
In figure 4, the authors have given error bars for the data meaning that those experiments were performed multiple times to ensure reliability of the data. On the other hand, in figure 5 there aren't any error bars. The authors should add error bars to the figure to show the fluctuations of the readings.
Author Response
Response to Reviewer 2 Comments
Point 1: The authors claim that this device is a rapid measurement system but at the same time the device requires a significant amount of sample preparation time and about 20 mins warm-up time. This claim is controversial since the user will need more than 1 hour to take measurements from soil samples. It is totally understood that 1 hour is clearly faster than the currently-used, lab-based methods and this a major advancement in the field. My suggestion is that the authors rephrase their manuscript to make this clear and eliminate any chances of misleading the reader.
Responses 1: After power is switched on, light beam from LED light source is not stable within a period of time, such as 20 minutes. In this experiment, a constant current source circuit with a three-terminal adjustable shunt regulator for driving LED was designed. However, the intensities of LEDs are affected by temperature of PN junction inside LEDs. Therefore, the warm-up time depends on the temperature of PN junctions. In the further, we are planning to apply laser diode as the light source. The intensity of the laser diode can be more stable because one photodiode (PD) is directly embedded into the laser diode to control the driving circuit.
In order to make this clear and eliminate any chances of misleading the reader, the following sentences have been added into the text. “After power is switched on, light beam from LED light source is not stable within a period of time, such as 20 minutes. In this experiment, a constant current source circuit with a three-terminal adjustable shunt regulator for driving LED was designed.” （Line 125-127, page 3）
Point 2:Equations 1, 2 and 3 are very common in the field and they do not need to be explained in that detail. For example, equation 1 and 2 are essentially the same equation. The authors should try to make that section more concise since the background theory is very well understood in the community.
Responses 2: After discussion with all authors, the equation 2 was deleted from this manuscript.
Point 3: Almost all equations and symbols in the manuscript need to be rechecked since sometimes they appear as text and sometimes as symbols. The authors should use a consistent method of presenting equations and symbols in the manuscript based on the journal's requirements.
Responses 3: All equations and symbols in the manuscript have been rechecked and symbols in the manuscript, such as I0, c, d, As, L and Cs have been rewritten based on the journal's requirements.
Point 4:In figure 4, the authors have given error bars for the data meaning that those experiments were performed multiple times to ensure reliability of the data. On the other hand, in figure 5 there aren't any error bars. The authors should add error bars to the figure to show the fluctuations of the readings.
Responses 4: In order to show the fluctuations of the readings, error bars have been added into Figure 5.
Author Response File: Author Response.pdf
Reviewer 3 Report
The work is interesting. Major revision is required as listed below:
Please explain what kind of LEDs you have used: model, features, price, ...
Please describe in more detail the circuits presented in section 2.4. I suggest you put graphs provided by the oscilloscope to explain and analyze the behaviours of the circuits.
Add a section or subsection to evaluate the cost of the prototype.
Minor issues:
In Equation 5 appears a parenthesis.
Line 256. Change "ForIn" to "In".
In line 127: "The multi-channel optoelectronic measurement system became ready to carry out absorbance measurements after a 20 min warm-up time". Why so much time is needed?
Author Response
Response to Reviewer 3 Comments
Point 1:Please explain what kind of LEDs you have used: model, features, price, ...
Response 1:The following sentence has been added into the Section of Materials and Methods.“A joint LEDs (light-emitting diodes) light sources (product model 5PRG9VCA-A40-M660-A405-T515) with the peak emission wavelengths of 405 nm, 660 nm and 515 nm, were purchased from Shenzhen Guanghui Sheng Electronics Co., Ltd with the price of 25 CNY”.（Line 98-101, page 3）
Point 2:Please describe in more detail the circuits presented in section 2.4. I suggest you put graphs provided by the oscilloscope to explain and analyze the behaviours of the circuits.
Response 2: Thank you for giving us suggestions. The behavior of the circuits was graphed as an inset in Figure 2a. The responding output voltages of the circuits were obtained from the standard phosphorus concentration of 0 (blank) ,4000 µg/L (C1),8000 µg/L (C2) ,12000 µg/L (C3) and 16000µg/L (C4) injected into the square spectrophotometer cells, respectively.
The following sentence has been added into the manuscript.
“The responding output voltages of the circuit were obtained from the standard phosphorus concentration of 0 (blank), 4000 µg/L (C1), 8000 µg/L (C2), 12000 µg/L (C3) and 16000µg/L (C4) injected into the square spectrophotometer cells, respectively (see the inset in Figure 2a). “（Line 174-177, page 5）
Point 3:Add a section or subsection to evaluate the cost of the prototype.
Response 3: In the Section of Construction of the optoelectronic measurement system, the cost of 700 CNY of this multi-channel optoelectronic measurement system was mentioned. （Line 212, page 7）
Point 4:In Equation 5 appears a parenthesis.
Response 4: We deleted the parenthesis in the equation 5 and correspondingly, the equation 5 was rewritten as
（Line 234, page 7）
Point 5: Change "ForIn" to "In".
Response 5: The “For” before “In” was deleted.
Point 6: "The multi-channel optoelectronic measurement system became ready to carry out absorbance measurements after a 20 min warm-up time". Why so much time is needed?
Response 6: After power is switched on, light beam from LED light source is not stable within a period of time, such as 20 minutes. In this experiment, a constant current source circuit with a three-terminal adjustable shunt regulator for driving LED was designed. However, the intensities of LEDs are affected by temperature of PN junction inside LEDs. Therefore, the warm-up time depends on the temperature of PN junction. In the further, we are planning to apply laser diode as the light source. The intensity of the laser diode can be more stable because one photodiode (PD) is directly embedded into the laser diode to control the driving circuit.
In order to make this clear and eliminate any chances of misleading the reader, the following sentences have been added into the text. “After power is switched on, light beam from LED light source is not stable within a period of time, such as 20 minutes. In this experiment, a constant current source circuit with a three-terminal adjustable shunt regulator for driving LED was designed.” （Line 125-127, page 3）
Author Response File: Author Response.pdf
Reviewer 4 Report
I would recommend to the authors to present the data in the tables with the same number of digits after the decimal point.
Author Response
Response to Reviewer 4 Comments
Point 1:I would recommend to the authors to present the data in the tables with the same number of digits after the decimal point.
Responses 1: The results shown in the Table 2 was revised with the same number of digits after the decimal point.
Table 2. Measurement results from both conventional lab-based methods and this photoelectronic measurement system.
Sample | Conventional method (mg /kg) | This method (mg/ kg) | ||||
P2O5 -P | K2O-K | NH4+-N | P2O5 -P | K2O-K | NH4+-N | |
1 | 29.48 | 120.00 | 54.26 | 20.72 | 163.60 | 79.56 |
2 | 45.89 | 129.60 | 51.79 | 37.93 | 164.50 | 68.67 |
3 | 23.75 | 165.60 | 61.66 | 22.50 | 181.90 | 93.08 |
4 | 40.99 | 159.20 | 44.39 | 39.87 | 187.30 | 77.40 |
5 | 39.67 | 104.40 | 38.22 | 28.69 | 123.00 | 53.13 |
6 | 25.66 | 117.60 | 46.86 | 24.88 | 145.50 | 69.40 |
7 | 22.69 | 169.20 | 15.73 | 23.54 | 183.20 | 23.30 |
8 | 14.40 | 92.40 | 17.27 | 17.29 | 118.00 | 20.03 |
9 | 11.47 | 85.20 | 13.70 | 12.65 | 101.60 | 18.52 |
10 | 99.07 | 104.40 | 33.52 | 69.02 | 123.00 | 31.04 |
11 | 56.55 | 88.80 | 6.17 | 49.68 | 95.50 | 22.09 |
12 | 15.47 | 120.60 | 8.26 | 19.16 | 137.20 | 20.84 |
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Dear Authors,
The article was suitably modified in accordance with the required reviews.
Best regards.
Author Response
Response to Reviewer 3 Comments
Point 1:English language and style are fine/minor spell check required
Response 1:
-“spread of” has been removed (Line 11, Page 1 in the revised manuscript)；
-“absolutely” was deleted (Line 13, Page 1 in the revised manuscript)；
- The following sentences “Crops often face significant challenges in obtaining an adequate supply of these nutrients to meet the demands of basic cellular processes. For this reason, the appropriate fertilizers should be applied to soil when nutrient deficiency may result in reduced crop yield. It is generally known that fertilizer application has become one of the most effective ways to increase crops production” have been replaced by “For this reason, the appropriate fertilizers should be applied to soil when specific nutrients are deficienct failure to which it may result in reduced crop yield. It is known that fertilizer application is one of the most effective ways to increase crops production”(Line 37-40, Page 1 in the revised manuscript)；
-“in excess of” has replaced with “more than”(Line 45, Page 2 in the revised manuscript)；
-“measurement data obtained from their farm's nutritive requirement” has been replaced with “scientific information gathered from their farm’s nutritive need”(Line 50-51, Page 2 in the revised manuscript)；
-“capacity” has been replaced with “ability”(Line 56, Page 2 in the revised manuscript)；
-“utilized” has been replaced with “used”(Line 78, Page 2 in the revised manuscript)；
-“ has high levels” has been replaced by “have elevated levels”(Line 90, Page 2 in the revised manuscript)；
-“ The extraction solution containing 0.45 M NaHCO3 and 0.374 M Na2SO4 ” has replaced with “The extraction solution having 0.45 M NaHCO3 and 0.374 M Na2SO4”(Line 95-96, Page 3 in the revised manuscript)；
-“ There is a LED driver circuit which produces the current pulses for each LED as long as the electric power supply is switched on” has been replaced with “The LED driver circuit produces the current pulses for each LED as long as the electric power supply is switched on.”(Line 159-160, Page 4 in the revised manuscript)；
- “ It can force the voltage there to be close to zero at all times” has been replaced with “ It can always force the voltage there to be close to zero.”(Line 175, Page 5 in the revised manuscript)；
- “in” has been replaced with “during”(Line 222, Page 6 in the revised manuscript)；
- “The experiment results indicate that correlations (R2=0.9010, 0.9471 and 0.8923) between absorbance at certain peak emission wavelengths of 405nm, 660nm and 515nm, respectively and respective nutrient concentration in soil samples were obtained” has been replaced by “The experiment results show high correlations (R2=0.9010, 0.9471 and 0.8923) between absorbance at certain peak emission wavelengths (405nm, 660nm and 515nm) and respective nutrient concentration in soil sample”(Line 311-312, Page 12 in the revised manuscript)；
- “in-house” was added into the text (Line 315, Page 12 in the revised manuscript)；
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
