Progress Report to the Maine Potato Board Research Subcommittee

January 12, 2007

Project Title:

Potato Management Studies with Emphasis on Nutrient Management, Supplemental Irrigation, and Crop Rotation

Investigators:

Gregory A. Porter and Paul C. Ocaya; Department of Plant, Soil & Environmental Sciences. University of Maine, Orono.

Executive Summary

Our research on crop rotation, supplemental irrigation, and nutrient management was continued during 2006. Five nutrient management experiments, two crop rotation experiments, and two other management experiments were conducted. Because of the wet growing season, supplemental irrigation did not result in significant improvements in yield and quality and we were not able to investigate the interactive effects of moisture supply and response to nitrogen fertility management. Russet Burbank showed a strong yield and quality response to increasing nitrogen rates. Delaying half of the nitrogen until just prior to first cultivation (early) or last hilling (late) had no effects on yield or quality. These results are similar to 2005. They show that when moisture supply is adequate there is considerable flexibility in the timing of N application to Russet Burbank potatoes. The results also confirm past research which shows that delaying 50% of the N does not increase yields when compared to the at-planting treatment. Removing half of the nitrogen, half of the phosphate, and all of the potash resulted in a 28 cwt/A yield increase in 2005 and a 30 cwt/A yield increase in 2006. No changes in tuber quality were observed in 2005; however the delayed fertilizer treatment significantly reduced specific gravity during 2006. One concern is whether similar results will be obtained when rainfall is less plentiful and uniformly distributed.

The field portion of our three-year gypsum and potash study was completed in 2006. Gypsum did not significantly affect yields, hollow heart incidence, or bruise susceptibility in these studies, but it did significantly increase tuber calcium concentration on a low soil-test calcium site. Our research has shown the potash can sometimes have strong yield and quality effects, including decreasing susceptibility to blackspot bruise and hollow heart. Shatter bruise susceptible varieties sometimes also show an increase in shatter bruise susceptibility in response to increasing potash rate. It is important to recognize that hollow heart incidence is primarily driven by weather conditions and varietal susceptibility. Nutrient availability can affect hollow heart susceptibility, but the effects of nutrients are typically less important than the effects of weather and variety.

Results from the crop rotation experiments are summarized below. A three-year rotation has provided slightly higher long-term yields that a standard, two-year potatoes grain rotation. Choice of rotation crop in a two-year rotation, did not significantly affect yields, but legumes grown in rotation with potato can contribute large amounts of N to subsequent potato crops. More detailed results are available upon request.

Project Objectives:

3. Develop rotation crop recommendations for potato production systems:

3a) Study potato responses to crop rotation and determine the effects of crop rotation and soil amendment use on soil properties.

3b) Conduct other rotation crop research as needed

Grant Received for 2006 Growing Season:

$26,123

Accomplishments to Date:

Five potato nutrient management experiments, two crop rotation experiments, and two cultural practices experiments were supported by Maine Potato Board research funds during the 2006 growing season. The project will result in improved nitrogen, potassium, and calcium fertility recommendations and tissue testing tools. We continue to focus on nutrient management effects on bruise susceptibility, fry color, and other quality attributes. The project also generates information on how to best manage new and established potato varieties and generates recommendations for crop rotations, including their influences on potato yield, quality, and disease incidence, as well as soil properties. As specific studies within the project are completed the results will be presented to the industry and published in various extension publications, popular, technical, and scientific outlets for use by the industry and other decision makers.

This report will focus on the results from our nitrogen fertilization experiment, calcium and potash experiment, and the two rotation experiments. Results from the other experiments will be made available as the studies are completed. More detailed results are available from the author.

Nitrogen Fertilization and Supplemental Irrigation Experiments. Supplemental did not significantly increase total or US#1 yield in our 2006 Russet Burbank experiment (Table 1). Rainfall was abundant and the lack of a yield response was not surprising. Irrigation did not affect tuber size, external defects, or hollow heart incidence during 2006. Response to supplemental irrigation depends largely on the weather conditions and, like the 1992, 2004, and 2005 growing seasons, the 2006 growing season was not a year that required supplemental irrigation.

The goal of this nitrogen fertilization experiment was to develop information to improve Maine’s tissue testing and fertilization recommendations for potatoes. In contrast to the 2005 experiment, the Russet Burbanks grown in this 2006 study showed a strong yield and quality response to increasing rates of nitrogen fertilizer (Table 1). Total yield and percent 10 oz increased to the highest rate of N applied, while US#1 yield was less responsive to N fertilizer (because higher N rates lead to higher incidence of misshapen tubers). Similar to our 2005 results, each 100 increment of nitrogen decreased Russet Burbank specific gravity by about 2 points (Table 1) . We observed high incidence of hollow heart during 2006 (Table 2). Incidence tended to be greatest in the low nitrogen treatments and lower as nitrogen rate increased, but incidence remained high at all nitrogen rates. These observations support the idea that hollow heart incidence is primarily driven by rainfall and temperature, but can by modified a bit by nutrient management.

Fry color and bruise susceptibility data are not available at this time of this report; however, in 2005 we observed that higher rates of nitrogen fertilizer resulted in slightly darker fry color from storage, greater susceptibility to tuber skinning, and increased susceptibility to shatter bruise. Once we have the fry color data from the 2006 experiment, we will caculate crop value for processing. We will also monitor the effects of nitrogen on fry color and tuber sugars from storage samples on a monthly basis to determine how long the effects of excess nitrogen last and whether storage temperature management can alleviate the effects of excess nitrogen. Tubers are being stored at two long-term holding temperatures (45 or 50F) with or without a 6 week precondition period at 55F.

Delaying half of the nitrogen until just prior to first cultivation (early) or last hilling (late) had no effects on yield or quality during 2006 (Tables 1 and 2). These results are similar to 2005. They show that when moisture supply is adequate there is considerable flexibility in the timing of N application to Russet Burbank potatoes. The results also confirm past research which shows that delaying 50% of the N does not increase yields when compared to the at-planting treatment. On the other hand, removing half of the nitrogen, half of the phosphate, and all of the potash resulted in a 28 cwt/A yield increase in 2005 and a 30 cwt/A yield increase in 2006. No changes in tuber quality were observed in 2005; however the delayed fertilizer treatment significantly reduced specific gravity during 2006. The yield increase from removing 50% of the nitrogen, 50% of the phosphate, and 100% of the potash from the fertilizer band has been surprising and should be studied further in future experiments. One concern is whether similar results will be obtained when rainfall is less plentiful and uniformly distributed.

Calcium and Potassium’s Effects on Bruising. In 2006, we completed the field portion of a three-year study on the effects of gypsum and potash on tuber yield, tuber calcium concentration, hollow heart incidence, and bruise susceptibility. This study has included four russeted and/or long-tuber-type varieties with a range of quality attributes. Research in Wisconsin has strongly implicated tuber calcium as being important in maintaining tuber quality (e.g. resistance to hollow heart, internal defects, and bruising). Our research shows that increasing rates of potash fertilizer result in improved internal tuber quality and blackspot bruise resistance, but that shatter bruise susceptibility can sometimes increase. Our studies also show that increasing rates of potash fertilizer not only increase tuber potassium concentrations, but also increase tuber calcium concentration.

The effect of gypsum and potash on yield, tuber size, specific gravity, and hollow heart incidence during 2006 is summarized in Tables 3 and 4. Most of the treatment effects observed in this study were variety effects. The varieties performed as expected with Russet Burbank providing the best overall combination of yield and quality. Reeves Kingpin had the lowest hollow heart incidence, but high levels of sunburn. Shepody also had high external defects incidence. GemStar Russet did well except that it had high incidence of hollow heart. As expected potash decreased specific gravity and also decreased hollow heart incidence. Potash did not eliminate hollow heart since this physiological disorder is primarily determined by varietal susceptibility and weather conditions. Gypsum did not affect yield, tuber size, specific gravity, or hollow heart incidence. Gypsum did not affect hollow heart incidence over the course of this three-year study. We do not have the bruise susceptibility and tuber calcium data for the 2006 experiment at this time, but results from 2004 and 2005 show no significant effect of gypsum on shatter bruise susceptibility (Table 5). As expected, potash application decreased blackspot bruise susceptibility (data not shown). Gypsum significantly increased tuber calcium concentration in 2004 (195 vs 155 mg kg^-1 d.w. basis) on a medium-low soil-test Ca site (1069 lbs/A soil test Ca, 38% base saturation), but did not significantly affect tuber calcium on a high soil test Ca site in 2005 (2538 lbs/A soil-test Ca, 75% base saturation). The 2006 study was conducted on a low soil-test Ca site (832 lbs/A soil-test Ca, 31% base saturation). This experiment was completed during the 2006 growing season and will not be repeated in 2007.

Nitrogen and Potassium’s Effects on Bruising and After Cooking Darkening. Our past research has shown that potash fertilizer can dramatically influence blackspot bruise susceptibility and can sometimes influence shatter bruising. Based on our research on tuber phenolics, tyrosine, and nutrient composition, we also feel that potassium would also likely influence after cooking darkening, an important quality attribute for fresh market and processing potatoes. The scientific literature provides evidence that nitrogen can also affect these tuber quality components and growers have long known that excess nitrogen can delay maturity, increase skinning, and increase the risk of shatter bruise. This experiment was initiated in 2005 and 2006 to continue our investigations on nutrient management effects on bruise susceptibility and tuber quality. Four rates of nitrogen fertilizer (0, 70, 140, and 210 lbs/A) were applied in combination with three rates of potash (0, 150, or 300 lbs/A). Two contrasting round-white potato varieties were used in this experiment to help us assess the effects on bruising and after cooking darkening: Ontario (shatter bruise resistant, after cooking darkening susceptible) and AF1758-7 (shatter bruise susceptible, after cooking darkening resistant, and blackspot bruise resistant).

AF1758-7 produced more attractive and uniform tubers than Ontario in this study. During 2005, AF1758-7 yield was maximized at 140 lbs/A of N following a timothy/clover plowdown, while Ontario yield showed little response to N rates greater than 70 lbs/A; however, both varieties showed a strong yield response to N in 2006 on a site which followed oats (Table 6). Potash rates of 150 lbs/A maximized yields of both varieties during 2005, but both varieties responded to the highest rate of potash in the 2006 study. During 2006, both varieties showed increases in tuber size in response to N and K. Specific gravity of both varieties declined with increasing potash rates, but was not greatly affect by N during 2006.

External tuber defects and hollow heart incidence of these round-white varieties was not greatly influenced by either N or potash; however, potash influenced the susceptibility of tubers to shatter bruise in 2006 (Table 7). Both nutrients affected skinning and shatter during 2005. As expected, AF1758-7 was more susceptible to shatter bruise than was Ontario.

After cooking darkening studies will be completed during winter 2007. We will also complete our shatter and blackspot bruise susceptibility studies. The results from the experiment will be used to help improve nutrient management recommendations to improve tuber quality. This experiment was completed during the 2006 growing season and will not be repeated in 2007.

Crop Rotation Studies: Our studies on the effects of crop rotation and soil management continued during 2006. One experiment (Table 9) using Superior and no irrigation demonstrates that mean US#1 yields over a 10-year period are highest (270 to 268 cwt/A) in a 3-year rotation or a 2-year rotation that received a single-year (1996) application of papermill sludge and compost. The two-year rotations with either oats or vegetables were equal (249 to 252 cwt/A) and the continuous potato treatment was worst (197 cwt/A). The goal of this experiment is to study the effects of one application of amendment and long-term crop rotations on both the soil and crop over time. We have studied soil fertility, organic matter, bulk density, and water stable aggregates in this experiment because one major set of crop rotation effects is on soil properties (data not shown). The results show that the low organic matter inputs and intensive tillage of a potato crop quickly decrease soil structure and organic matter. Surprisingly, extending the rotation to three years and including one year of timothy/clover (which adds organic matter and provides a full year without tillage) has quickly improved soil organic matter and structure. Yield and quality improvements from the three-year rotation have been modest. The amendment treatment quickly enhanced soil properties, but its effects have declined over time as expected. Yields have remained higher than the standard rotation. Table 9 summarizes that potato yield response from 1996-2006. The results clearly show the seasonal fluctuation in yields that results primarily from erratic rainfall (e.g. 1999, 2001, and 2002 were dry years with low yields) , that soil improvement approaches (crop rotation and soil amendment) cannot substitute for an adequate water supply, and that yields are more stable in the amended treatment and three-year rotation. The soil management approaches clearly have more subtle effects on productivity than rainfall patterns; however, differences in yields among the rotation treatments are evident. External defects incidence has been markedly increased in the continuous potato treatment in recent years (sunburn in 2004; pink rot in 2005; sunburn and pink rot in 2006). We have also looked at rhizoctonia incidence and severity in this experiment. The continuous potato rotation had significantly higher incidence and severity than the others in 2006, but there were no significant differences among the other rotations (data not presented). These and other results from this experiment should help growers and the industry make rational choices regarding crop rotation, amendment application, water use, and land management programs in the coming years.

We are continuing our studies on selected two-year rotations and their impacts on soil properties and potato productivity (cv. Shepody). Potatoes are currently rotated with oats, oats underseeded with Italian ryegrass, peas/clover, and a oat/pea/vetch green manure in this study. Short-term effects have been primarily on N fertility. The green manure crop has decreased the need for nitrogen fertilizer by 40 to 60 lbs/A relative to the oat rotation, but none of the two-year crop rotations have increased tuber yields at the optimum rate of N fertilizer. High rates of N fertilizer in combination with any of the rotation crops tended to decrease specific gravity without improving yield (data not shown). Tuber size tended to increase with increasing rate of N. Depending on the rotation and the year, specific gravity decreased by 3 to 4.6 points per 100 lbs of N fertilizer applied. As N fertilizer rate increased, a greater fraction of the N taken up by the crop remained in the tops rather than being removed in the tubers (i.e. nitrogen use efficiency declined dramatically from 60-70% to near 30%). Detailed results are available on request. These two-year rotations have not had dramatic effects on soil organic matter or structure to date. Starting with the 2006 rotation crops we have substituted canola and Caliente mustard into this experiment to look at how these crops effects will affect potato yield, nitrogen response, and disease incidence. Results from these rotations crops will first be available after the 2007 growing season.

Cultivation and Hilling Experiment with Shepody, Reeves Kingpin, and AF1808-18. Reeves Kingpin and AF1808-18 have been tested in commercial trials as possible replacements for Shepody. Both have strengths but each has experienced a range of problems. One of the observed problems with all three varieties is susceptibility to sunburning. This experiment was designed to determine if hilling program could reduce sunburning of these three varieties. The hilling programs compared were: 1) standard, cultivation plus early and late hilling; 2) cultivation plus early one-pass hilling; and 3) cultivation plus late one-pass hilling. During 2005, hilling program did not affect total yields; however, the standard program had the highest US#1 yields and the single-pass early program had the lowest US#1 yields. The only quality attribute affected by hilling program was sunburning. The standard program had the lowest sunburning incidence, while the single-pass early program had the greatest. The single-pass early program was particularly a problem for sunburning of AF1808-18. Results from the 2006 experiment are not presented in this report because of space limitations. This experiment was completed during the 2006 growing season and will not be repeated in 2007.

Additional Potato Nutrient Management Experiments. Three other experiments with varying nutrient management programs were conducted in 2006. In one study, we continued our research on nitrogen and potash effects on yield and quality of Atlantic chipping potatoes. In the second, we continued our studies on nitrogen’s effects on yield and processing quality of Shepody potatoes. Results from these experiments have been reported in the past and presented at the Maine Potato Conference and other grower meetings. In another experiment we grew potatoes at a range of soil pH ranging from about 5.0 to 7.0 to document the crops response to soil pH. These experiments are part of our long-term studies on potato nutrient management and will be made available to the Maine Potato Industry through extension publications, technical reports, scientific publications, and improved nutrient management recommendations.

Table 1. Supplemental Irrigation and Nitrogen Treatment Effects on Yield, Percent Stand, Tuber Size, and Specific Gravity of Russet Burbank Potatoes. Aroostook Research Farm, Presque Isle, ME -- 2006.

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Irrigation and Yield (cwt/A)¹ Percent Tuber Size Distrib. (% wt. Basis) Specific

Nitrogen Total US#1 US#1 Stand <2" 2" to > 10 >3" >3.5" Gravity

Treatments >2" (June 19) 10 oz. oz. Long Long

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Irrigation Main Effect (n=32):

Check 365 303 248 99 19 58 23 78 62 1.094

Irrigated 373 309 258 99 17 59 23 81 66 1.090

Nitrogen Treatments² [lbs/A, (n=8)]:

At-Planting Broadcast

0 221 199 124 99 38 55 7 63 43 1.094

75 365 314 246 99 22 66 12 71 51 1.096

150 382 322 271 99 16 59 25 82 67 1.093

225 393 315 269 99 15 57 29 83 68 1.093

300 421 332 293 99 12 52 36 86 74 1.088

75 75 early 388 322 278 100 14 61 25 83 67 1.093

75 75 late 370 303 253 98 16 60 24 83 68 1.091

75-75-0 75-75-200 early 412 339 292 100 14 59 27 85 71 1.089

LSD_0.05 30 39 34 ns 3 4 5 4 6 0.003

AOV Results³:

Irrigation ns ns ns ns ns ns ns ns ns ns

Nitrogen Treatment ** ** ** ns ** ** ** ** ** **

**LQC **LQC **LQC ns **LQC **LQC **L **LQ **L **L

* *Q *Q

Irrig. X Nitrogen ns ns ns ns ns * ns ns ns ns

ns ns ns *L ns **Q **Q ns ns ns

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¹US#1 yield was calculated as total yield minus yield of tubers with external tuber defects (external defects are listed in Table 4).

²Nitrogen treatments were either at planting, early (before first cultivation), or late (before last hilling). All treatments received at total of 150 lbs/A P₂O₅ and 200 lbs/A K₂O.

³Significance of AOV F-tests is presented were: ns=no significant effect; * and ** indicate significance at P<0.05 and <0.01, respectively. Nitrogen rate response was tested using trend analysis where: L=linear; Q=quadratic; C=cubic. Pr>F is presented for AOV results when Pr>F is between 0.05 and 0.1.

Table 2. Irrigation and Nitrogen Effects on Percent External Defects (% weight basis) and Percent Hollow Heart (% count basis) by Size Class of Russet Burbank Potatoes. Aroostook Research Farm, Presque Isle, ME -- 2006.

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Irrigation External Tuber Defects. (% wt. Basis) Percent Hollow Heart by Size Class (% by Count)¹

and Nitrogen Total Sun- Mis Growth Scab Rot < 2" >2" to 10 oz. > 10 oz. Overall

Treatments burn -shapen Cracks tubers tubers tubers

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Irrigation Main Effect (n=32):

Check 16.6 4.7 8.1 3.6 0.0 0.3 0.6 8.8 39.3 8.0

Irrigated 16.9 3.4 7.4 4.3 0.0 1.8 1.9 13.8 53.6 12.4

Nitrogen Treatments² [lbs/A, (n=8)]:

At-Planting Broadcast

0 9.6 2.2 3.7 3.6 0.0 0.1 0.0 27.5 60.6 12.3

75 13.9 4.6 4.1 4.7 0.0 0.5 3.8 6.3 54.9 7.5

150 15.7 2.6 8.4 2.5 0.0 2.2 0.0 20.0 38.8 14.6

225 19.9 5.1 9.9 3.8 0.0 1.1 0.0 5.0 43.8 7.8

300 21.1 3.1 13.4 3.7 0.0 0.9 0.0 5.0 27.5 7.1

75 75 early 17.6 5.1 6.7 4.0 0.0 1.8 2.5 8.8 47.5 11.0

75 75 late 18.1 4.0 8.4 4.4 0.0 1.2 2.5 12.5 46.3 11.7

75-75-0