Hesitant To Leave Zero Strips In Test Plots?

Many people are very concerned about leaving zero strips in field test plots because of the perceived impact on crop yield. As well, it is thought to lead to other problems, such as weeds that grow better where there is less crop competition.

Researchers and extension people will tell you how important zero strips are to really understand what the impact of test input treatments are. Are they right? What information will I gain and what will I lose?

Nitrogen Rate Strip Trials

Let’s evaluate this based on nitrogen (N) strip trials that were done across the province this past summer. The impact on corn yields from various nitrogen rates applied at planting or side dress time is summarized in Table 1. The concept was to look at nitrogen rates on cooperator farms relative to the rates they had been using in the past. We looked at rates of 0, 0.5, 1.0, and 1.5 times the cooperator’s normal nitrogen rate. Although everyone’s "normal" rate of nitrogen differs, lets assume that on average this rate is around 100 lbs. per acre (lbs/ac) of nitrogen plus a starter value of about 30 lbs./ac.

Table 1 – Corn yield impacts from various N rates.

Soil Type	# of Sites	N Rate Category	Yield (bu/ac)	0 base (% ^ over 0 rate)	0.5 base (% ^ over 0.5 rate)
Fine	5	0.0	118.4
	5	0.5	139.5	18
	5	1.0	151.0	28	8
	5	1.5	149.4	26	7
Medium	9	0.0	89.9
	9	0.5	109.1	21
	9	1.0	113.3	26	4
	9	1.5	111.0	23	2
Course	3	0.0	117.4
	3	0.5	141.3	20
	3	1.0	147.3	25	4
	3	1.5	144.8	23	2
All	17	0.0	103.1
	17	0.5	123.8	20
	17	1.0	130.4	26	5
	17	1.5	128.3	24	4

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If you look at the "All soil types" data, even with only starter fertilizer we got 103 bushels per acre (bu/ac). Increasing the N to half (0.5X) of the normal rate increased yield by 20%. The normal rate (1.0X) gave a 26% increase in yield over the zero rate. The 1.5X rate did not give us any extra yield over the normal (1.0) rate.

Now, is this valuable information to have? If I had started with the half (0.5) rate as my lowest rate, I really wouldn’t know what kind of response the field is naturally able to provide. Based on the half (0.5) rate as the base, I am only seeing a 5% yield response to nitrogen. I really wouldn’t have any information that would give me confidence that I can lower my nitrogen rate.

There was a good response to the half (0.5) rate over the zero strips, but the full rate did not give that much additional yield. Based on N costs and yield, I can calculate whether it paid to put that extra nitrogen on. Now I have some valuable data to work with, which may help me shave my nitrogen rates in future years.

On your farm you will likely only have 1 test per year. But if you run a test every year for a few years, you should get a good feel for whether your target nitrogen rates are in the ball park.

Figure 1 - Corn yield impacts from various N rates – all soil types

As illustrated in Figure 1, across all soil types, we see there is an initial response to adding N, but that it levels off somewhat between the 0.5 and 1.0 X rates. This suggests that we could maybe be targeting the 0.75X rate as our best rate.

Figure 2 - Corn yield impacts from various N rates – by soil types

Figure 2 illustrates the trends across the various soil types. The medium (M) textured soil has a flatter response curve, indicating less response to N. The fine (F) and course (C) textured soils seem to get greater response to increasing rates of nitrogen, although they are based on less tests then with the medium textured soils. I now have some very valuable information to use in my decision making process.

Yield Losses From Zero Strips Minimal

So what did this information gathering cost me? Did I lose big yields, which would deter me from continuing to add in zero strips? Let’s pencil it out. Assume that the test plot is a 25 acre field that was 1500 feet long and 725 feet wide. The strips were put in the long way to get the most out of the plot. Placing them down the 725 foot distance would have less impact.

Two 12 row strips at 30 feet each by 1500 feet would equal 2.07 acres (60*1500/43560) in the zero strip segments. This represents 8.3% of the total field area (2.07/25*100). Therefore, if no yield at all was harvested off these strips I would be losing a maximum 8.3% of my total field yield. However, if we use the "All Soils" value of 26% less yield in the zero strips compared to the full rate strips, I still received 74% of my anticipated yield. So the overall impact on the total yield would be 2.16% (8.3*26/100). This does not take into account the added time of actually changing rates and putting in the plot. More information on some ways to do this better and more efficiently will be included in the next issue.

Valuable Information Gained

Therefore 2.16% yield was sacrificed in order to gain the valuable information that may allow me to reduce my nitrogen rates by 30 to 50 lbs./ac. Seems like it pencils out! Placing the strips down the 725 foot length of the field would have resulted in about half that impact and likely similar N response.

Zero strips can be used with fertilizer, insecticides, fungicides, tillage and any number of other things you want to look at. They are a valuable tool in understanding what is really going on in your fields and provide a base of knowledge from which you can make informed decisions.

They should be an important consideration!