Progress Report to the Maine Potato Board Research Subcommittee

Progress Report to the Maine Potato Board Research Subcommittee

January 20, 2006

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

Five potato nutrient management experiments, two crop rotation experiments, and two cultural practices experiments were supported by Maine Potato Board research funds during the 2005 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.

Nitrogen Fertilization and Supplemental Irrigation. Rainfall was abundant at Presque Isle during 2005 and supplemental irrigation only slightly increased total yield and did not significantly affect U.S.#1 yields in our 2005 Russet Burbank experiment. The lack of a major yield response was not surprising given the wet conditions. Supplemental irrigation increased the percentage hollow large-sized tubers from 2.5 to 6.9%. The Russet Burbanks grown in this study had more vigorous foliage as nitrogen rate increased; however, too much nitrogen fertilizer decreased yield and specific gravity. Each 100 increment of nitrogen decreased Russet Burbank specific gravity by 2.2 points. Higher rates of nitrogen fertilizer increased percent 10 ounce, increased tuber skinning and shatter bruise susceptibility, increased the incidence of misshapen tubers, and resulted in slightly darker fry color. We are monitoring the effects of nitrogen on fry color and tuber sugars from storage samples 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 and few effects on quality during 2005. 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 with no change in tuber quality. Information from this nitrogen fertilization experiment will help to improve Maine’s tissue testing and fertilization recommendations for potatoes.

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. In 2005 we continued our investigations on nutrient management effects on bruise susceptibility and tuber quality. Four rates of nitrogen fertilizer were applied in combination with three rates of potash . Two contrasting round-white potato varieties, AF1758-7 and Ontario, were used in this experiment to help us assess the effects on bruising and after cooking darkening. AF1758-7 produced more attractive and uniform tubers than Ontario in this study. 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. Increased potash rates increased tuber size of both varieties. Both nutrients influenced the susceptibility of tubers to external damage (skinning and shatter). As expected, AF1758-7 was more susceptible to shatter bruise than was Ontario. Shatter bruise susceptibility was not affected N rate, but potash rate increased shatter susceptibility of both varieties. After cooking darkening and blackspot bruise susceptibility will be measured during the winter months.

Calcium, Potassium and Nitrogen Effects on Bruising and Quality. Our research shows that increasing rates of potash fertilizer result in improved internal tuber quality and bruise resistance. Our studies also show that increasing rates of potash fertilizer increase tuber calcium concentration. A 2005 experiment continued our studies on potash’s effects on tuber calcium concentration and bruise susceptibility. We also studied gypsum application as an alternative approach to increasing tuber calcium and presumably decreasing bruise susceptibility. Data are not reported at this time because laboratory results on tuber nutrient composition are not available yet. Two other experiments with varying nutrient management programs were conducted in 2005. One study was on the effect of nitrogen and potash on tuber quality of Atlantic, while the other was on nitrogen’s effects on yield and fry color of Shepody.

Crop Rotation Studies: Our studies on the effects of crop rotation and soil management continued during 2005. One experiment using Superior and no irrigation demonstrates that mean US#1 yields over a 9-year period are highest (260 to 261 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 (243 to 246 cwt/A) and the continuous potato treatment was worst (208 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 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. We are studying these effects of crop rotation on soil properties and soil-borne disease in both experitments.

Cultivation, Hilling, and Other Practices. Reeves Kingpin and AF1808-18 have been tested in commercial trials as possible replacements for Shepody. An 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. Shepody and Reeves Kingpin had similar external defects incidence, while AF1808-18 had much higher incidence, primarily due to sunburn. 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 results of this experiment confirm that Reeves Kingpin offers yield, tuber size, and specific gravity advantages over Shepody as long as stands are good and tuber size is controlled. The standard program had the lowest sunburning incidence, while the single-pass early program had the greatest. An experiment was conducted in which sixteen potato varieties and clones were evaluated to determine their sensitivity to post-emergence herbicide applications. Two were sensitive to postemergence metribuzin (Sencor) and two were moderately sensitive (data not presented). One clone was sensitive to foliar rimsulfuron (Matrix) and five were moderately sensitive; however, none of the clones showed any significant yield loss from foliar rimsulfuron.

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 2005 Growing Season:

$25,000

Accomplishments to Date:

Nitrogen Fertilization and Supplemental Irrigation Experiments. Supplemental irrigation slightly increased total yield and did not significantly affect U.S.#1 yields in our 2005 Russet Burbank experiment (Table 1). Rainfall was abundant and the lack of a major yield response was not surprising. Irrigation did not affect U.S. #1 yields, percent 10 oz, or specific gravity during 2005; however, irrigation increased the percentage hollow large-sized tubers (2.5% vs 6.9%; Table 2). Response to supplemental irrigation depends largely on the weather conditions and, like the 1992 and 2004 growing seasons, the 2005 growing season was not a year that required supplemental irrigation. Our long-term weather data suggest that supplemental irrigation is beneficial in about 7 out of every 10 years in central Aroostook County.

The goal of this nitrogen fertilization experiment was to develop information to improve Maine’s tissue testing and fertilization recommendations for potatoes. Even though the Russet Burbanks grown in this study had more vigorous foliage as nitrogen rate increased (data not shown), the 2005 results show that too much nitrogen fertilizer decreases both yield and specific gravity. Each 100 increment of nitrogen decreased Russet Burbank specific gravity by 2.2 points (Table 1) . Our data from 2005 also show that higher rates of nitrogen fertilizer increased percent 10 ounce (Table 1) and increased the incidence of misshapen tubers (Table 2).

Higher rates of nitrogen fertilizer resulted in slightly darker fry color from December 2005 storage, greater susceptibility to tuber skinning, and increased susceptibility to shatter bruise (Table 3). We will monitor the effects of nitrogen on fry color and tuber sugars from storage samples 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. We are monitoring tuber sugars and fry color on a monthly basis.

Delaying half of the nitrogen until just prior to first cultivation (early) or last hilling (late) had no effects on yield and few effects on quality during 2005 (Tables 1 and 2). The only significant effect on quality was an increase in hollow heart caused by the later nitrogen timing. 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 with no change in tuber quality. These results show demonstrate that growers have flexibility in timing nitrogen applications when moisture is readily available, but that there is no benefit in yield or quality from delayed nitrogen applications. These results are consistent with past studies in Maine. The yield increase from removing 50% of the nitrogen, 50% of the phosphate, and 100% of the potash from the fertilizer band was surprising and will have to be confirmed in future experiments.

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 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. 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 (Table 4). Potash rates of 150 lbs/A maximized yields of both varieties. Tuber size of Ontario increased in response to increasing N rates, while tuber size of AF1758-7 did not. Increased potash rates increased tuber size of both varieties. Specific gravity of both varieties declined with increasing nitrogen and potash rates. The lack of responsiveness of AF1758-7 to increasing nutrient levels may have been due to injury caused by European corn borer (ECB). It was much more seriously injured by ECB than Ontario. Whether this is due to greater susceptibility or simply due to its growth stage at the time of the ECB egg laying is not know at this time. We believe that the ECB damage to AF1758-7 limited its yield and tuber sizing in this experiment. Normally, yields are expected to be similar to those of Ontario.

External tuber defects and hollow heart incidence of these round-white varieties was not greatly influenced by either N or potash; however, both nutrients influenced the susceptibility of tubers to external damage (skinning and shatter, Table 5). As expected, AF1758-7 was more susceptible to shatter bruise than was Ontario. Skinning of Ontario was more strongly affected by N rate than was that of AF1758-7 (N response of AF1758-7 may have been limited by ECB damage) . Shatter bruise susceptibility (measured as incidence of thumbnail cracks and air cracks following tumbling in a drum) was not affected N rate, but potash rate increased shatter susceptibility of both varieties.

After cooking darkening will be measured during the winter months. We will also measure blackspot bruise susceptibility and conduct additional measures of shatter bruise susceptibility. The results from the experiment will be used to help improve nutrient management recommendations to improve tuber quality. This experiment should be repeated in 2006.

Calcium and Potassium’s Effects on Bruising. 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 bruise resistance. Our studies also show that increasing rates of potash fertilizer not only increase tuber potassium concentrations, but also increase tuber calcium concentration. This study was designed to continue our studies on potash’s effects on tuber calcium concentration and bruise susceptibility. We are also studying gypsum application as an alternative approach to increasing tuber calcium and presumably decreasing bruise susceptibility. Data are not reported at this time because laboratory results on tuber nutrient composition are not available yet. Results will be reported next year.

Additional Potato Nutrient Management Experiments. Two other experiments with varying nutrient management programs were conducted in 2005. 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 has been reported in the past and presented at the Maine Potato Conference and other grower meetings. The research is 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.

Crop Rotation Studies: Our studies on the effects of crop rotation and soil management continued during 2005. One experiment (Table 6) using Superior and no irrigation demonstrates that mean US#1 yields over a 9-year period are highest (260 to 261 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 (243 to 246 cwt/A) and the continuous potato treatment was worst (208 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 6 summarizes that potato yield response from 1996-2005. 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). We have also looked at rhizoctonia incidence and severity in this experiment (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. 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, but we anticipate that their effects will increase over time.

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. Reeves Kingpin had the most vigorous vines, highest total and US#1 yields, and highest specific gravity of the three varieties in 2005 (Tables 7 and 8). Total yields of Reeves Kingpin exceeded those of Shepody by 39 cwt/A, while US#1 yields were higher by 29 cwt/A. Reeves Kingpin and AF1808-18 had larger tuber size than Shepody. Shepody and Reeves Kingpin had similar external defects incidence, while AF1808-18 had much higher incidence, primarily due to sunburn. 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. The results of this experiment confirm that Reeves Kingpin offers yield, tuber size, and specific gravity advantages over Shepody as long as stands are good and tuber size is controlled. The standard, two-pass hilling program resulted in less sunburn than a single early or late hilling. This experiment should be repeated in 2006.

Metribuzin/Rimsulfuron Sensitivity Study. Sixteen potato varieties and clones were evaluated in 2005 to determine their sensitivity to post-emergence applications of metribuzin (e.g. Sencor) and rimsulfuron (e.g. Matrix). Results from this type of experiment help UM and industry make recommendations concerning herbicide applications and they also are useful to our variety development efforts as we make decisions about commercial testing and management profiles for new breeding lines. Of the sixteen clones tested in 2005, two were sensitive to postemergence metribuzin (Sencor) and two were moderately sensitive (data not presented). One clone was sensitive to foliar rimsulfuron (Matrix) and five were moderately sensitive; however, none of the clones showed any significant yield loss from foliar rimsulfuron.

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 -- 2005.

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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" (July 6) 10 oz. oz. Long Long

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Irrigation Main Effect (n=32):

Check 363 328 290 100 11 61 27 81 66 1.079

Irrigated 375 322 285 99 12 59 30 84 70 1.077

Nitrogen Treatments² [lbs/A, (n=8)]:

At-Planting Broadcast

0 352 323 279 99 14 66 20 78 58 1.086

75 392 351 313 99 11 64 26 81 67 1.079

150 367 333 294 99 12 57 31 83 68 1.077

225 359 295 263 100 11 58 31 84 70 1.074

300 346 279 251 100 10 52 38 86 73 1.074

75 75 early 371 333 298 100 11 62 27 84 70 1.077

75 75 late 369 332 294 100 12 62 26 81 66 1.078

75-75-0 75-75-200 early 395 352 309 99 12 60 28 84 72 1.078

LSD_0.05 24 32 31 ns 3 5 6 3 5 0.002

AOV Results³:

Irrigation .06 ns ns ns ns ns ns * * ns

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

.1L **L **L .1L *L **L **L **L **L **LQ

*QC *Q *Q

.08C .06C

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

.07C .08LC .06Q

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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 -- 2005.

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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 10.0 1.4 7.5 0.7 0.0 0.4 0.0 0.0 2.5 0.3

Irrigated 14.2 1.7 10.5 1.5 0.0 0.4 0.0 0.9 6.9 1.4

Nitrogen Treatments² [lbs/A, (n=8)]:

At-Planting Broadcast

0 8.1 0.9 6.5 0.6 0.0 0.1 0.0 0.0 7.5 0.6

75 10.5 1.5 7.3 1.5 0.0 0.1 0.0 0.0 7.5 1.0

150 9.4 0.8 6.6 1.4 0.0 0.5 0.0 0.0 5.0 0.7

225 17.7 2.9 13.5 1.1 0.0 0.2 0.0 0.0 6.3 0.7

300 19.4 2.0 16.1 0.8 0.0 0.5 0.0