Seeding Rate Effects on Forage Mass and Vegetation Dynamics of Cool-Season Grass Sod Interseeded with Sorghum-Sudangrass

Round 1

Reviewer 1 Report

line 51 maybe should be changed to may be

line 70 insert the word of i.e. brown midrib lines of forage sorghum hybrids

line 77 delete the word of i.e. how seeding rates affect

lines 93-94 reword to say: The existing sod where we established the experiment had been mowed periodically during spring 2016, but had not been fertilized.

line 148 Figure 1 title should have years 2016, 2017 not 2015,2016

lines 166, 169, 170: Should refer to Figure 2, not Figure 1

line 213,214 say nutritive value at end of sentence.

Author Response

We made each of this reviewer's suggested revisions.  Thank you for the review and close attention to detail.

Reviewer 2 Report

The paper describes a straightforward experiment investigating the effect, in terms of seedling density, subsequent DM production and cool-season sward composition the following year, of sowing rate of an annual warm season grass into a closely-mown cool-season grass sod in late spring at a Nebraska site in a strategy aimed at increasing summer forage production.

Use of warm season grasses to boost summer production in temperate climates in the USA appears to be an area of interest at present. This study makes a worthwhile contribution to this research and is appropriate to this journal.  Measurement of effects on cool-season grass sward composition was an interesting extra dimension. The statistical analysis is sound and the paper is well written. My only reservation concerns the use of a single site/year combination which reduces the robustness of the conclusions. This concern is diminished by the thorough discussion of the results in relation to results of other studies. Nevertheless it is a pity a matching experiment was not conducted at Mead where a related study was conducted, and which sounds to have had much higher emergence rates. Higher emergence rates at Lincoln may have altered the shape of the DM response curve or where its maximum occurred.

Note that “value” as in nutritive value is missing on line 214.

Author Response

Thank you for the review and comments about the research.  We added "value" to line 214 as suggested.

Reviewer 3 Report

The manuscript "Seeding rate effects on forage mass and vegetation dynamics of cool-season grass sod interseeded with sorghum-sudangrass" addresses an important approach to improving summer-forage production and is, generally, well written.

I noted and indicated a few minor corrections including more clarity on methods. It may be helpful to readers if authors included a justification for the total population count in assessing seedling density instead of sample-based estimates that would also have excluded the border-rows, L104-106.

Likewise, some details on the sampling frame dimensions and actual rows captured, L108.

The M&M is missing details on how the percentage germination reported in Table 2 was determined, L151

Comments for author File: Comments.pdf

Author Response

We made the following revisions based on this reviewer's comments:

1. We added the width of the frequency frame, 75 cm, and noted that it was initially placed in the center on one end of each plot, covering the five middle rows, before flipping over end-to-end three times.
2. The reviewer pointed out that sampling border rows when determining plant density may be misleading due to edge effect.  We concur that this often occurs in plot studies and considered reanalyzing the data to remove the border rows.  However, plots were managed nearly the same with the exception of seeding rate and initial mowing height of the non-mowed control and therefore concluded edge effects were likely negligible.  The timing of plant density sampling also took place early in the study before differences in light availability and shading might have accrued due to the seeding rate differences.  Therefore, we made no change in the manuscript or data analyses with respect to this point.  Although a subsampling method would have been quicker than sampling the whole plot for density, we observed some variability among rows and decided sampling the whole plot and counting all sorghum-sudangrass individuals would not require a large time demand.
3. The reviewer asked for more details to how emergence was computed.  Therefore, we added the statement: Emergence percentage was computed by dividing plant density by seeding density, assuming 38,062 PLS kg^-1 to the Materials and Methods section.
4. We corrected minor edits to grammar as requested.