Efficiency of Phosphorus Use in Sunflower

Round 1

Reviewer 1 Report

Figure 1 in 2016 appears not to have any rainfall.  Is this correct?

Lines 236-238 appear to be from the template itself and not part of the paper.

For your equations in section 2.4 you state that the - PAsP and each other second term in equations 1-4 is representing without P added.  But I do not see anywhere that a 0 P is measured.  So is this the 50 kg/ha or is the 0 data not shown?

I also think you should show the actual harvest data and not just the efficiencies.  I say this because a farmer does not care only about efficiency but also economic return.  See all the work done by Roger Sylvester-Bradley, doi https://doi.org/10.1093/jxb/erp116.  As an example.  The economic optimum is far more important that the nutrient efficiency and all crops show better efficiency at the low end of fertilization.

Showing the data also tells the reader if the cultivar is better at responding to the fertilizer or better and maintaining a yields and less responsive to the nutrient levels.  See https://www.jstor.org/stable/90001992 as an example.  

Author Response

1. Yes, is right. The meteorological data presented in figure 1 are from the period in which the experiment was conducted, from September to December 2016, during this period it is common not to occur rains at the study site.

2. The misconception has been fixed.

3. PAsP é a produtividade de aquênios de girassol without the application of P₂O₅ (0 kg ha^-1). 0 kg ha^-1 is a component in the equation to calculate the efficiencies.

4. The suggested examples were consulted. This research involving nutritional efficiency shows sunflower productivity in relation to P availability and detects differences between cultivars for achene productivity. The farmer obtains a greater economic return with high productivity. The calculated efficiencies can be considered to inform farmers and readers because the best efficiency is results of obtaining maximum productivity under an adequate level of nutrients. Agronomic efficiency (AE) is also called economic efficiency. Their results express the economic production obtained (production of sunflower achenes) per unit of applied nutrient.

Reviewer 2 Report

The paper is written correctly and I have only a few remarks:

- since the work is based on the effectiveness of different doses of phosphorus, the soil chemical properties need to be described in more detail, primarily according to the class of soil supply with macro nutrients

- the depth of sampling was not sufficient (0-20 cm) and  it is not a relevant indicator for sunflowers whose root system permeates the soil to a depth up to 2 m

- it is necessary to explain how certain fertilization treatments are determined (according to the chemical properties of the soil: pH and phosphorus content) : (0, 50, 100, 150, and 200 kg of ha^-1 P₂O₅)

- if the paper in the chapter materials and methods states 5 doses of phosphorus, then why in the results and discussion we talk about 4 doses, So, why the results are not related to the control treatment ( 0 kg P₂O₅ ha^-1)

- in conclusion, the dose of 50 kg P ha^-1 ( low dose of P fertilizer) is stated as the most effective and it would be advisable to link this conclusion with the content of plant-accessible phosphorus in the studied sites for a more detailed explanation

Author Response

1. To supply the soil with macronutrients were used, urea as a nitrogen source, of which 60 kg ha^-1 was between two applications as follows: 20 kg ha^-1 at the plantation and 40 kg ha^-1 50 days after emergence. For the potassium source, potassium chloride was used, and 50 kg ha^-1 was applied at planting according to the recommendation for the crop [45]. For the phosphate fertilization, simple superphosphate was used, and the amounts were applied according to the treatments studied. More information was added to the manuscript.

2. The soil was collected before the experiment was set up to quantify the nutrient content in the 0-20 cm depth layer because the accumulation of nutrients in the surface layers is greater due to the immobility and low solubility of its compounds, especially in acidic soils and with high clay contents, and the greatest chemical and physical changes in cultivated soils occur at this depth.

3. In the study site, the available P content for plants is generally less than the minimum available P content required for satisfactory crop production. Soils present P sorption decreases the efficiency of phosphate fertilization, for this reason, it was determined to apply doses of 50, 100, 150, and 200 kg ha^-1 P₂O₅.

4. The misconception has been fixed. Five doses of phosphorus were evaluated, the dose of 0 Kg ha^-1 P₂O₅ (without the application of P₂O₅) is used in the equation to calculate the efficiencies. As shown in the description of the components of the equations.

5. A more detailed explanation was added during the discussion of the results.

Round 2

Reviewer 1 Report

I still think you need to put the actual yields in the paper.  (Point 4)  

Author Response

4. The productivities were added to the article.