Progress Report to the Maine Potato Board Research Subcommittee

January 2005

 

Project Title:                     Integration of Crop Rotations using Barley, Soybean, and Forage Rotation Crops into Potato Production Systems.

 

Investigators:

     A. Randall Alford, Dept. of Biological Sciences

     A. Alyokhin, Dept. of Biological Sciences

     T. Dalton, Dept. of Resource Economics & Policy

     M.S. Erich, Dept. of Plant, Soil & Environmental Sciences

     E. Gallandt, Dept. of Plant, Soil & Environmental Sciences

     E. Groden, Dept. of Biological Sciences

     D.H.  Lambert, Dept. of Plant, Soil & Environmental Sciences

     G.A. Porter, Dept. of Plant, Soil & Environmental Sciences (project coordinator)

     S. Smith, Dept. of Resource Economics & Policy

 

Executive Summary:

 

                A large-scale, cropping system experiment (15 acres, 96 plots) was continued on Aroostook Research Farm in Presque Isle during the 2004 growing season.  This experiment compares soil management systems, crop rotations, and pest management systems.  The soil management systems compared are a conventional, chemically fertilized system versus an amended system that receives manure and low rates of chemical fertilizer.   Three crop rotations are compared: 1] two-year standard (potatoes-barley); 2] four-year intensive (potatoes-soybean-potatoes-barley); and 3) four-year integrated (potatoes-soybean-barley-alfalfa).   An integrated pest management system (IPM) using conventional chemicals is compared to an environmentally-friendly pest management system (ENV) that uses fewer and/or less toxic pesticides. 

 

            Soil analyses show that the amended system has significantly higher soil organic matter, cation exchange capacity, Modified Morgan available P, and soil-test K, Mg, and Ca.  Soil pH, S, B, and Zn were also significantly increased by the amendment program and it has also consistently increased soil aggregation and lowered soil bulk density.   During the relatively wet 2004 growing season, we saw no significant improvements in yield in the amended management system; however, the four-year average yields for the amended system are 26 cwt/A higher than the conventional system even though three out of the four growing seasons have been relatively wet.  The average N, P2O5, and K2O fertilizer rates were reduced by 59, 100, and 87% in the amended system.   Soil management system did not affect incidence blight or white mold incidence during 2004, but amendments increased powdery scab root gall incidence and rhizoctonia stem infection.  Unlike other recent years, the soil management systems did not affect  CPB or other insect populations.  The crop rotations  had no significant effects on yield or tuber quality during 2004 or over the past four years.  We have also seen very few effects of rotation on diseases and insects in this experiment.  Crop rotations did affect aphid numbers in 2004, but had no effect of CPB populations.  The data show that soybeans can be included in potato rotations with no short-term yield loss and that short-term potato yields do not benefit from including forage legumes in the rotation and extending the crop rotation to one year of potatoes in four.   On a cautionary note, the data are from only the first cycles through these rotations and differences should become more prevalent in subsequent rotation cycles. 

 

            The 2004 and four-year average results show that yield and quality were not significantly reduced in the ENV pest management system despite a 49 to 99% reduction in the fungicide active ingredient load compared to the IPM system, the use of less toxic insecticides, and cultural controls for weed management.  Pest management system did not affect the incidence of blight, white mold, powdery scab, or rhizoctonia during 2004.    CPB, aphid, and fleabeetle incidence were often similar for the pest management systems; however, in 2004 ENV had higher aphid populations, but lower CPB populations than the IPM system. Weed control in the potato crop was very good in ENV, but ENV was not as effective at controlling weeds in the barley and soybean rotation crops.  The results show that many of the synthetic chemicals used in potato production can be replaced with other inputs; however, there may be increased costs (e.g. CPB control products) and there is the potential for some yield loss (20 cwt/A average over the four-year study and not statistically significant in any of the individual years) and increased risk from alternative pest management programs. 

 

Project Objectives:

            1).        Continue a long-term, large-plot, research study focusing on Maine potato cropping systems by examining:

                        1a)       The impact of crop rotation length on potato yields, quality, pests and soils.

                        1b)       The use of soybeans and forages as additional rotation crops in a potato-production system and their effects on potato yields, quality, pests and soils.

                        1c)       The impacts of these crop rotations on soil quality with or without additional organic matter in the form of animal manure.

 

            2).        Develop an understanding of crop performance and potato pest ecology in an IPM-pest management system compared to a reduced chemical pest management system.

 

Grant Received:

 

            $6,000

 

Progress Report for the 2004 Growing Season:  

 

Crop Rotation and Soil Management Systems:  The 2004 field season was the second field  season that we could evaluate the full range of crop rotation and soil management treatments designed into this experiment (soil management: amended vs. nonamended; crop rotations: barley-potatoes; barley-potatoes-soybean-potatoes; soybean-barley-forage-potatoes).  The data collected from 2003 and 2004 represent the system performance in the first full cycle through the four-year rotation schemes.  The data will be most useful when compared as an average over each four-year cycle (e.g. the average from 2001 to 2004 would represent the potato performance in the first cycle though each four-year rotation).  If the experiment is continued that long, the average from 2005 to 2008 would represent the average performance of potato through the second full cycle of each four-year rotation.  

 

            The 2004 field season represents the sixth full year in the new soil amendment program.  The non-amended soil management system used an average of 170-120-235 lbs/A (N,P2O5 K2O, respectively) supplied as chemical fertilizer (combined preplant, at-planting, and sidedressed application).  The amended system averaged 40 tons/A manure (f.w. basis) and received an average of 70-0-0 supplied as chemical fertilizer.  Relative to the non-amended system, the manure application and the past fertility built up in the amended system resulted in the following reductions in chemical fertilizer use during 2004: Nitrogen 100 lbs/A (59%), 120 lbs/A P2O5 (100%), and 235 lbs/A K2O (100%).

 

            These plots receive no supplemental irrigation; however, 2004 was a relatively moist growing season.  Despite the high rainfall, crop vigor was clearly better in the amended compared to the non-amended system, especially through the latter third of the season.

 

Experimental Description –2004 Potato Cropping Systems Study

 

15-acre cropping systems study, 96 plots

Aroostook Research Farm, Presque Isle, ME

 

Planted:            June 8 to 9, 2004

Variety:            Atlantic

Vinekilled:         September 17, 2004 (100 days after planting)

Harvested:        October 15-19, 2004

 

Pest Management Systems

 

            IPM vs. BIO (“Environmentally Friendly”)

 

                                    IPM                             ENV “Environmentally Friendly”

            Insects              higher thresholds           lower thresholds

                                    Provado 1.6F                Bt

                                    Asana                           Beauveria bassiana

                                                                       

            Disease                        chlorothalonil                 azoxystrobin

                                    EDBC                         

                                    Total a.i.=10.5 lbs/A      Total a.i. = 5.4 lbs/A (approx. 49% reduction)

 

            Weeds              PE, metribuzin               cultivation - Lely (75% of plots 1X; 25% of plots 3X)

                                    cultivation (1X)              cultivation - between rows (2X)

                                    hilling 2X                       hilling 2X

 

Soil Management System

 

            No amendment vs. amended (manure; reduced fertilizer rate)

           

            Non-amended: 170-120-235 (lbs/A of N-P2O5 -K2O, respectively).

            Amended:         40 tons/A manure (f.w. basis)

                        70-0-0 supplied as ammonium sulfate.  Relative to the non-amended system, the manure application and the past fertility built up in the amended system resulted in the following reductions in chemical fertilizer use during 2004: 100 lbs/A (59%), 120 lbs/A P2O5 (100%), and 235 lbs/A K2O (100%).

 

Crop Rotations:

 

            IPM System:

            1) standard (two-year with grain)                                               potatoes-barley

            2) intensive (potatoes 2 out of 4 years plus soybean)                    potatoes-soybean-potatoes-barley

            3) extended (potatoes 1 in 4 years plus soybean and forage          potatoes-soybean-barley-alfalfa

 

            BIO System:

            3) extended (potatoes 1 in 4 years plus soybean and forage          potatoes-soybean-barley-alfalfa

 

History:

 

1991-1998 Old Design               last full report published covered 1991-1994

                                                last journal paper covered up to 1996

 

New Design:

 

1998                 new design rotation crops planted

1999                 transition year, second year of new standard, intensive, and extended rotations

2000                 transition year, third year of  new standard, intensive, and extended rotations

2001-2004         first complete cycle of intensive and extended rotations

each year generates a full set of data comparing crop rotations

                        four-year averages are the most appropriate measure of rotation performance

2005-2008         second complete cycle of intensive and extended rotations

each year generates a full set of data comparing crop rotations

                        four-year averages are the most appropriate measure of rotation performance

 

 

Soils:   The comparison of the amended versus non-amended management systems allows us to determine how an “organic matter rich” system will respond compared to a conventional, short-rotation, fertilizer-based soil management system.  The non-amended system is typical of that used on most commercial farms in the area.  It is our reference or standard system.  The amended system has received “long-term” applications of manure and/or compost (since 1991) and low rates of chemical fertilizer.  This system might be typical of one used in future “sustainable” programs, organic production, or conventional farming integrated with animal-based agriculture.

 

Results: Soil test results from the 2004 crop year have not been received at the time of this report.  Soil analyses from the 2003 crop year show that the amended system has significantly higher soil organic matter, cation exchange capacity, Modified Morgan available P, and soil-test K, Mg, and Ca (Table 1).  Soil pH, S, B, and Zn were also significantly increased by the amendment program (data not shown).  These results are consistent with past data and similar results are expected for the 2004 samples.  We have also consistently seen greater soil aggregation and lower soil bulk density (Table 2).  Soil moisture levels are typically higher early in the season and after rainfall events (data not shown).   Crop rotation effects on soil properties are already showing up during the 1st four-year rotation cycle (Table 1).  The rotations with the higher frequency of potato production (e.g. two-year standard and four-year intensive) have received greater cumulative manure applications over time in the amended system and consequently these rotations have higher fertility levels than the four-year integrated rotation (potatoes appear only once every four years in this rotation).

 

 

Table 1.           Effect of  soil amendment and crop rotation system  on soil organic matter and fertility.  Potato Ecosystem Project - 2003 samples.

______________________________________________________________________________

 

                                                Percent             Cation         Soil Test Results (lbs/A)

                                                Organic                        Exchange          Avail.     K       Mg        Ca

                                                Matter              Capacity     P

                                                                        (Meq/100g)

______________________________________________________________________________

Soil Mgt.

No amendment                         2.7                      7.5            32.2            498       275       1729

Amended                                  4.8                    11.2            63.3            779       527       3225

 

Rotation    Soil Mgt.

2-year (std)       Check               2.6                      7.3            30.4            508       267       1692

4-yr. Intensive   Check               3.0                      7.9            34.5            554       269       1701

4-yr. Integrated Check               2.6                      7.4            32.0            464       282       1761

2-year (std)       Amended          5.5                    12.6            75.3            961       595       3592

4-yr. Intensive   Amended          4.7                    11.5            67.0            747       537       3244

4-yr. Integrated Amended          4.5                    10.4            55.4            704       487       3033

 

AOV Results:

Soil Mgt.                                   **                     **               **               **         **         **

Rotation                                    ns                     .07              *                **         na         ns

Rotation x Soil Mgt.                   .10                    .06              *                **         ns         ns

______________________________________________________________________________

 

 

 

Table 2.           Effect of  soil amendment and crop rotation system  on soil bulk density and water stable aggregates.  Potato Ecosystem Project - 2003 samples.

______________________________________________________________________________

 

                                                Bulk Density     Bulk Density                 Water Stable Aggregates

                                                May 15             June 25                         % d.w. basis

                                                All                    Potato

                                                Plots                 Plots

______________________________________________________________________________

Soil Mgt.

No amendment                         1.11                  0.99                              25.3

Amended                                  0.96                  0.93                              38.5

 

Rotation    Soil Mgt.

2-year (std)       Check               1.10                  0.99                              26.2                 

4-yr. Intensive   Check               1.11                  1.01                              22.6

4-yr. Integrated Check               1.13                  0.98                              26.2     

2-year (std)       Amended          0.86                  0.89                              40.2

4-yr. Intensive   Amended          0.90                  0.91                              37.0

4-yr. Integrated Amended          1.03                  0.98                              38.4

 

AOV Results:

Soil Mgt.                                   **                     .09                                **

Rotation                                    *                      ns                                 ns

Rotation x Soil Mgt.                   .09                    ns                                 ns

______________________________________________________________________________

 

 

Potato Crop: We measured plant emergence, stands, and percent ground cover during the growing season.  Petiole samples, leaf samples, foliage samples, and tuber samples were collected for nutrient analysis.  The crop was harvested, weighed and graded to measure yield and tuber quality.  Potato tubers were placed in storage and the incidence of superficial tuber diseases was measured.

 

Results:   Summary yield and quality data from 2004 are presented in Table 3.  During the relatively wet 2004 growing season, we saw no significant improvements in yield in the amended management system.  There were also relatively few soil amendment effects on tuber quality.  The amended system did slightly increase scab incidence, but it did not affect the overall incidence of external tuber defects.  The amended system also had significantly higher tuber specific gravity.  Considering the four-year period from 2001 to 2004, total yields were higher (26  cwt/A) in the amended soil management system compared to the non-amended system (Figure 1) even though the average N, P2O5, and K2O fertilizer rates were reduced by 59, 100, and 87% (2004 rates presented in Figure 2).   These data show that manure and soil nutrient reserves can effectively replace fertilizer nutrients and that potato yields can be increased by the use of organic soil amendments even when low chemical fertilizer rates are used.  The data also show that the yield benefits from the use of soil amendments are greater during dry years (e.g. 2001) than wetter years (e.g. 2003 and 2004).   This differential effect reflects higher soil organic matter content, improved soil structure, and greater water holding capacity.

 

The crop rotation and pest management systems had essentially no significant effects on yield and tuber quality during 2004 (Table 3).  The data presented in Figure 3 show that three-year average yields have not differed among the rotation treatments. These data show that soybeans can be included in potato rotations with no short-term yield loss.  The data also suggest that potato yields do not benefit in the short-term from extending the crop rotation to one year of potatoes in four and including forage legumes in the rotation.  This is surprising, since we expected and have seen in other experiments that less frequent potato production can reduce pest incidence and improve soil physical properties.  The lack of rotation effect in this experiment may be due to the relatively short duration of the rotation treatments.   All four years represent the first cycle through the rotation length comparison.  If the experiment is continued from 2005 through 2008, we would be studying the second cycle through the four-year rotation and greater crop rotation effects would be expected.  

           

The 2004 results show that yield and quality were not significantly reduced in the ENV pest management system despite a 49% reduction in the fungicide active ingredient load compared to the IPM system, the use of biological insect control, and cultural controls for weed management (Table 3).  Over the three-year period (2001-2004), we saw no significant yield loss from the ENV pest management; however, the IPM program had a slight numerical advantage in yield (20 cwt/A, Figure 4).  The results show that many of the synthetic chemicals used in potato production can be replaced with other inputs; however, there may be increased in costs (e.g. CPB control products) and there is the potential for some yield loss (though not statistically significant in our study).  There also may be increased risk from alternative pest management programs in terms of disease spread (e.g. increased virus disease spread if ENV fails to effectively control aphids) or disease outbreaks (e.g. although the ENV program has been effective at controlling early and late blight from 2001 through 2004, we do not know how it would hold up under heavy disease pressure).  If these changes in pest management practices are to occur, growers would need to receive a higher price for their efforts or other programs would need to be enacted to foster riskier, but more environmentally benign approaches.


Table 3.           Potato yield and quality as affected by pest management, soil amendment, and crop rotation.  Potato Ecosystem Project, Aroostook Research Farm, Presque Isle, ME.  2004 Growing Season.

                                                                                                                                                                         

                                                    Yield (cwt/A)            % Ext. Defs.     Size  Distribution (%)  Spec.

                                                Total     US#1    US#1    Total    Scab     1f     2¼     2½             Grav.

                                                                        >2¼ "                           to 4"   to 4"   to 4"

                                                                                                                                                                                                                                                           

Pest Management System

Comparison:

 

IPM pest mgt.                           318       247       213        8.8        3.1       84.8      73.4      64.5      1.095

ENV pest mgt.                          308       227       200        9.9        1.5       82.0      72.2      63.5      1.097

 

No Amendment                         299       236       202        7.5        1.1       85.5      73.4      64.0      1.092

Amended                                  316       245       213        8.8        4.0       84.8      73.9      64.9      1.099

 

            AOV Results:

            Pest Mgt.                      ns         ns         ns         ns         ns         ns         ns         ns         ns

            Soil Mgt.                       .07        ns         .10        ns         *          ns         ns         ns         **

            Pest. x Soil                    ns         ns         ns         ns         ns         ns         ns         ns         ns

 

Soil Management within

the IPM System:

 

No Amendment                         299       236       202         7.5      1.1        85.5      73.4      64.0      1.092

Amended                                  316       245       213         8.8      4.0        84.8      73.9      64.9      1.099

 

Two-year Rotation1                   304       236       205         8.8      2.7        85.5      74.2      64.9      1.095

Four-yr intensive Rotation2         300       238       205         6.8     1.8        85.2      73.3      63.9      1.095

Four-year Rotation3                   318       247       213         8.8      3.1        84.8      73.4      64.5      1.095

 

            AOV Results:

            Soil Mgt.                       ns         ns         ns           ns       *          ns         ns         ns         **

            Rotation                        ns         ns         ns           ns       ns         ns         ns         ns         ns

            Rot. x Soil                     ns         ns         ns           ns       ns         ns         ns         ns         ns

                                                                                                                                                            

External defects in the pest management sequence: sunburned tubers were the most prevalent defects [percent sunburned tubers was affected by pest management p<.01 (increased in ENV) and soil management at p<0.05 (decreased in AMD)].  External defects in the soil management sequence: sunburned tubers were the most prevalent defects [percent sunburned tubers was significantly affected by soil management at pr<.06 (decreased in AMD)]

1 Barley-Potato Rotation (in place since 1991 growing season)

2 Barley-Potato-Soybean-Potato  (started in 1999, 2004 data are the sixth year of testing a complete four-year rotation cycle; however, the plots are in second cycle through this rotation).

3 Soybean-Barley-Forage-Potato (started in 1999, 2004 data are the sixth year of testing a complete four-year rotation cycle; however, the plots are in their second cycle through this rotation).

 

 

Text Box: Text Box: Text Box: Text Box: Potato Disease Management:      From 1995-98, disease management in the BIO system was based on frequent application of Cu-containing compounds.  This provided a comparison versus standard synthetic fungicides.  The program was successful in that we had few problems with the major foliar diseases on potato, late blight and early blight.  Unfortunately, the BIO system tended to be associated with earlier crop senescence and significant reductions in crop yields during most years from 1991-1998.  The result was a system that was not economically viable in our analysis of short-term returns.   Because of the significant yield loss commonly observed in the BIO system from 1991-98 and because we felt that a disease management program so heavily based on a persistent metal (Cu) was undesirable, we modified the BIO system into an “environmentally-friendly” system, synthetic-chemical-based system (ENV) and have used that system since 1999.    Disease management in the ENV program uses minimal rates and frequencies of chlorothalonil and strobilurins with application frequencies dependent on disease pressure forecasts.  This program is similar to that developed in Wisconsin in conjunction with the World Wildlife Fund. The ENV pest management system has been very effective in providing disease control, while reducing the fungicide inputs during periods when disease pressure has been low.  Active ingredient applications have typically been reduced by 60% in each growing season.   The active ingredient reduction was 49% during 2004.