Soil Amendment - Crop Rotation Effects on Productivity - Soil Properties Within Potato Production Systems

Final Report for LNE98-103

Project Type: Research and Education
Funds awarded in 1998: $100,126.00
Projected End Date: 12/31/2002
Matching Non-Federal Funds: $48,942.00
Region: Northeast
State: Maine
Project Leader:
Gregory A. Porter
University of Maine
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Project Information

Summary:

Soil amendment and crop rotation practices for potato production were studied in two research station experiments. Emphasis was placed on yield effects, nutrient uptake, and soil changes occurring several years after amendment applications had ceased. For non-irrigated potatoes, the annual amendment program (AMEND) with the highest use of compost and manure provided the greatest US#1 yield response (+41 cwt/A) relative to no amendments (NONE), greatest fertilizer savings (52%), and most dramatic effects on soil properties; however, this program was very expensive due to the costs of amendment purchase, hauling, spreading, and incorporation. An amendment program for four years followed by a four-year reliance on residual effects (SASP) also improved US#1 yields (+35 cwt/A) and soil properties. A single year application of compost/manure (ONCE) or compost plus paper mill sludge provided more modest US#1 yield increases (14 and 21 cwt/A, respectively) and improvements in soil properties. These less intensive amendment programs (SASP, ONCE, and paper mill sludge) had much lower costs than the AMEND program. Some of the yield improvements provided by amendments appears to be due to improved boron availability; however, it is likely that improvements in soil physical properties and changes in soil biology contribute to the response. Partial budget analysis using conservative potato prices ($6.17/cwt) and the expensive prices that we paid for compost and showed that AMEND resulted in a small net loss relative to NONE; however, its relative profitability would be favorable if potato prices increased or if the cost of amendments decreased. The less intensive amendment programs (SASP, ONCE, or paper mill sludge) were more profitable than NONE even using the conservative potato price. They become even more profitable with higher potato prices or lower amendment prices. These results show that the use of composts, manures, and paper mill sludge can be advantageous in Maine potato production. Supplemental irrigation provided substantial yield benefits in these studies, but did not affect soil fertility or physical properties. The US#1 yield response to AMEND (36.5 cwt/A) was slightly smaller under irrigated conditions than it was under non-irrigated conditions. A green manure rotation crop provided no yield advantages or improvements in soil physical properties relative to the standard oat rotation.

Amendments affect soil organic matter, bulk density and aggregation, so it is expected that they will improve water infiltration and soil moisture retention. Effects on water infiltration rates, runoff, and sediment removal were studied using a rainfall simulator. No significant differences in infiltration rate were detected for amended versus non-amended plots. Sediment removal tended to be lower in the amended system. Measured phosphorus losses in runoff were of concern in both amended and non-amended systems. Phosphorus concentrations in runoff were increased by the amended systems, probably as a result of increased surface soil fertility.

A three-year crop rotation was compared to the standard, two-year rotation common to the area. After a single crop rotation cycle, the three-year rotation produced 13 cwt/A higher US#1 yields than the two-year rotation. Soil and crop sampling indicated that this probably resulted from improvements in soil physical properties and late-season nitrogen availability. The advantages of the three-year rotation would be expected to increase as several more rotation cycles occur. Partial budget analysis using conservative potato prices shows that the yield advantage of the three-year rotation could support additional land rental to expand the rotation length. Lease or purchase of additional land would be more favorably supported at higher potato prices and/or if the yield response increased after several additional rotation cycles.

Farmers identified critical questions concerning soil management and helped design and conduct trials using manures and paper mill sludge on commercial farms. Results from the entire project were disseminated to the Maine potato industry and others via presentations, tours, field days, publications, and web sites. The presentations alone accounted for over 1100 grower/professional contacts while many more people were made aware of soil organic matter issues via the other information outlets. We expect that the information developed will be extremely valuable to growers and decision-makers considering strategies for building soil organic matter and replacing chemical fertilizers as nutrient sources.

Introduction:

Due to intensive cultivation and short cropping cycles, potato production in the Northeast can lead to excessive soil erosion, loss of organic matter, and poor aggregation which can limit productivity and result in negative effects on ground and surface water. Research conducted at the University of Maine and on growers’ farms has provided ample evidence that soil fertility and physical properties can be improved when composts and manures are applied. Yields in these amended systems are almost always higher than conventionally managed systems; however, short-term economic analyses typically show lower profits due to the relatively high costs of amendments. The economic situation would be favorable, if long-term or “residual” benefits due to amendments were included in the analysis (e.g. benefits to soil fertility, soil physical properties, and crop yields which persist for several cropping cycles). Beneficial crop rotations would be expected to have similar effects, though they would likely occur only after much longer time periods. In this project, we studied the residual effects of soil amendment programs and crop rotations in two research station trials on potato production systems. Emphasis was placed on yield effects, nutrient uptake, and soil changes occurring several years after amendment applications have ceased. A three-year crop rotation was also compared to the standard, two-year potato grain rotation that is common in the area. Partial budgets were created to provide an economic analysis of the research station experiments. Amendment effects on water infiltration rates, runoff, and sediment removal were studied using a rainfall simulator. Farmers identified critical questions concerning soil management and helped design and conduct trials on commercial farms. Results were disseminated to the Maine potato industry and others via presentations, tours, field days, publications, and web sites.

Project Objectives:

1a) Research will be conducted on the effects of crop rotation and soil amendments (compost, manure, and paper mill sludge). For soil amendments, special emphasis will be on effects occurring several years after applications have ceased (i.e. residual effects), because these effects will be critical to the economic viability of soil amendment use on commercial farms.

1b) Farmers will identify critical questions concerning the commercial use of soil amendments and rotation crops. They will help design and conduct trials using soil amendments and new crop rotations on commercial potato farms.

1c) An economic analysis of the research data will be completed and results of the entire project will be disseminated to the Maine potato industry via presentations, discussion groups, and publication of an Extension fact sheet.

2) Water infiltration rates, runoff, and sediment removal will be compared for several crop rotation schemes and for amended versus non-amended soils under potato production.

Research

Materials and methods:

This project consisted of two experiments on the Aroostook Research Farm (Maine Agricultural and Forest Experiment Station), Presque Isle, Maine; research trials on commercial farms; and extension education efforts.

Research Station Experiment #1– Crop Rotation, Supplemental Irrigation, and Soil Amendment (Compost and Manure) Effects on Potato Soils. This experiment was established during 1992-93 with potato (cv. ‘Superior’) as the test crop. The design had subplots consisting of a factorial combination of soil amendments (unamended vs. amended with 10 and 20 tons per acre of cull potato compost and cattle manure, respectively) and crop rotation treatments (oats vs. green manure). The 1992-95 experimental goals were to use the soil amendment and crop rotation treatments to increase soil organic matter and determine if these inputs could increase productivity and/or substitute for supplemental irrigation in a potato production system (for results see Porter et al., 1999; Opena et al, 1999). The soil amendment treatments were modified in 1996 to continue the original experimental goals and to begin a study of the residual effects of soil amendments. From 1996 to 2000, the soil amendment treatments were: 1) NONE, no amendment; 2) ONCE, amended during 1996 only, a test of the residual effects of a short-term program; 3) SASP, amended from 1992-96 only, a test of the residual effects of a long-term program; and 4) AMEN D, amended from 1992-2000, a long-term amendment program. Effects on soil properties measured duirng the 1996 and 1997 growing seasons were reported by Grandy et al. (2002). The current project supported the 1999 and 2000 growing seasons and represent data from the second/third cropping cycles not receiving amendments [see Grandy et al. (2000) and the Appendix for details of management practices, crop and soil sampling, etc.]. The comparison of two rotation crops and non-irrigated versus irrigated potato production continued during 1999 and 2000.

Research Station Experiment #2– Crop Rotation Effects and the Residual Effects of Compost and Paper Mill Sludge Application. This experiment was established during 1996 to compare several cropping sequences for potato production (cv. ‘Superior’). The cropping sequences were: 1) continuous potatoes; 2) 1:1, potatoes rotated with small grains; 3) 2:1, potatoes rotated with small grains that are undersown with clover/timothy and then a full year of clover/timothy; 4) 1:1, potatoes rotated with commercial vegetable crops consisting of peas or broccoli in alternate years; 5) 1:1, potatoes rotated with small grains and receiving a single application of soil amendments. The amendment application within treatment #5 occurred during 1996 and consisted of 10 tons per acre of cull potato compost applied in the spring and 60 tons per acre of paper mill sludge applied in the fall. During the 1999 and 2000 growing seasons, we studied the effects of the crop rotations on potato production and also the residual effects of the 1996 soil amendment application. Data obtained were from the 3rd and 4th growing seasons after the amendment applications. More detailed methods and information on crop and soil data collection are provided in the Appendix.

Trials on Commercial Farms. A small group of potato growers (30 to 40) in the central Maine and southern Aroostook County, Maine areas worked with UM Extension on a range of issues relating to soil organic matter management, crop rotation, and manure use. These growers received information from our past soil management research, identified significant practical questions related to new crop rotations and soil amendment use on a large scale, and helped design the commercial trials conducted within the project. Commercial-scale trials with manure and other amendments were conducted during each growing season. Farmers were involved in trial implementation, data collection, and interpretation.

Economic Analysis. An economic analysis of the soil amendment programs was conducted using partial budgets (Boehlje and Eidman, 1984; Este et al., 1996). Only the enterprise components affected by the management practices under study were included in the analysis. The budgeting included yield and quality effects over several cropping cycles for the experiment station trials, since the objective of these experiments was to determine if residual benefits occur several years after amendment application ceases.

Objective 2. The major activities for this objective were carried out in the summers of 1999 and 2000. In 1999, four rainfall simulation tests were carried out in early June before plants emerged and from July 26 through August 5 (early tuber bulking). Three tests were successfully carried out during late July-early August. The volumes of runoff for these tests were limited to the upper limit of rain intensity of 2.45 cm/hr that the simulator could handle. The three successful tests provided infiltration information for two treatment plots that were unamended and one treatment plot that had been amended for all of the previous six years. Runoff sample collection was successful for two amended and two unamended plots. The tested plots were all planted to potatoes in 1999 and had been in the oat rotation the previous year.

The rainfall simulator was improved during 2000 to allow a higher rainfall intensity. The 2000 rainfall simulator test intensity was 7.1 cm/hr. The 2000 year testing was carried out from June 24-July 14 for plots planted to potatoes. In this year, testing was more successful and 10 plots were tested. Six of the plots tested had the amended treatment and the other 4 plots were unamended. The plots had been planted to oats or barley in the previous year.

Research results and discussion:

Milestones:

Conduct Experiment Station Study #1 on soil amendment, crop rotation, and supplemental irrigation use in potato systems (Objective 1a) and study infiltration, run-off, and sediment movement (Objective 2). Completed during 1999 and 2000 as planned. Results are summarized below and additional details are attached as part of the Appendices.

Conduct Experiment Station Study #2 on soil amendment and crop rotation use for potatoes (Objective 1a). Completed during 1999 and 2000 as planned. Results are summarized below and additional details are attached as part of the Appendices.

Work with small groups of farmers to identify significant soil amendment and crop rotation related questions and finalize design of commercial trials (Objective 1b). Cooperative Extension faculty interacted extensively with small groups of farmers that were interested in amendment use, crop rotation, diversification, and soil organic matter. These growers helped develop the questions addressed in the applied research and outreach program. This took place during 1999 through 2002.

Conduct research trials on two commercial farms (Objective 1b). Cooperative Extension faculty conducted applied research on two commercial farms and on the University of Maine’s Rogers Farm during 1999 and 2000.

Complete laboratory and data analysis for the experiments (Objectives 1a, 1b, and 2). Laboratory and data analyses were begun during 1999, but because of many complications could not be completed until late 2002. Results are summarized below and additional details are attached as part of the Appendices.

Complete an economic analysis of the project results (Objective 1c). Partial budgets were constructed during 2002 and 2003. Results are summarized below and additional details are attached as part of the Appendices.

Deliver educational programs and materials to Maine growers, including discussion sessions, tours, formal presentations and a fact sheet summarizing soil management research and amendment applications for potato systems(Objective 1c). Presentation of educational programs and materials to Maine growers and other audiences took place throughout the project from 1999 to 2002. A summary is provided below under Objective 1c and Section 8. Publications/Outreach.

Submit final project report. Completed during February 2003 and sent March 2003. This was intended to be done in February 2001, but was formally delayed to February 2002 due to delays in laboratory analyses and other problems. Subsequent difficulties resulted in a further delay to the February/March 2003 date.

Results:

Objective 1a. Experiments on crop rotation and amendment use were conducted at Aroostook Research Farm in Presque, ME during the 1999 and 2000 growing seasons. Soil samples were collected and analyzed for inorganic N, mineral nutrients, organic matter, bulk density, and water stable aggregates. Plant tissue samples were collected and analyzed for nutrient content. The following is a brief description of the experiments and results (additional details are attached in the Appendices):

Experiment #1 — Crop Rotation, Compost, Manure, and Supplemental Irrigation Effects on Potato Production Systems. This study compared the following compost (10 t A-1)and manure (20 t A-1) amendment treatments: i) NONE, no amendments; ii) ONCE, amended during 1996 only; iii) SASP, amended from 1992-1995 then no amendments; iv) AMEND, amended each cropping year since 1992. The major objective was to determine how long the positive effects of amendments would last and whether single-year applications would perform as well as multiple-year applications. Two-year rotations of potato-oats versus potato-green manure (P/V/O – pea/vetch/oats) were also compared as were supplemental irrigation treatments. A detailed summary of the results is presented in the Appendix.

Contrary to past years, amendment did not significantly increase US#1 yields or have major tuber quality effects during 1999. AMEND did significant increase US#1 yields compated to NONE during 2000 (+46 cwt/A under non-irrigated production). All amended treatments had numerically higher US#1 yields than NONE during both years; however, the difference was not great enough to be statistically significant above the background variation in the field (e.g. two-year average US#1 yield relative to NONE, +25 cwt/A for ONCE; +19 cwt/A for SASP; +35 cwt/A for AMEND). As we have observed in past years, potatoes within two-year rotations performed as well following oats as following green manure. The results show that potato yield and quality can be maintained in amended systems while reducing chemical fertilizer use (e.g. for the oat rotation -40% ONCE, -12% SASP, and -52% AMEND).

Supplemental irrigation was evaluated as an alternative to soil amendment application in this experiment. US#1 yields were not affected by irrigation during the wet 1999 growing season; however, it increased US#1 by 46 cwt/A (either with or without amendment) during the drier 2000 season. The US#1 yield for non-irrigated potatoes in the AMEND program was equal to that in the irrigated, unamended system during 2000. These results suggest that an aggressive soil amendment program can build soil organic matter and fertility, resulting in less need for supplemental irrigation during dry years. Our research shows that potatoes grown in an amended system are less stressed and higher yielding than unamended potatoes during dry years; however, the results also show that the yield response to irrigation was the same (+46 cwt/A) for non-amended and amended plots. Clearly, the benefits of the AMEND program do not completely substitute for crop water supply (rain or supplemental irrigation). It appears that the beneficial effects of AMEND (e.g. increased soil nutrients, higher soil organic matter, lower bulk density, and increased aggregation) are helpful under irrigated, as well as non-irrigated conditions.

Soil organic matter showed a fairly nice relationship reflecting the intensity of amendment application (AMEND > SASP > ONCE > NONE). Amendments also significantly affected water stable aggregate content (WSA) and total soil carbon (%T-C) during 2000. The continuous amendment program (AMEND) had the strongest effects on soil organic matter and physical properties. AMEND significantly affected soil bulk density, WSA, percent total carbon, and percent organic matter content. The trends show that once soil organic matter has been increased through a single application (ONCE) or multiple applications (SASP), residual effects on soil physical properties will be observed through at-least two rotation cycles. Based on the yield response noted above, these soil properties had relatively small effects on yield and quality during 1999 and 2000. Based on our past research and the observed differences in soil properties, we would expect greater yield responses in the amended plots during dry growing seasons. The green manure rotation crop and supplemental irrigation treatments had no major effects on soil organic matter or physical properties.

Surprisingly, we observed no amendment effects on soil pH, CEC, or soil-test K, P, Ca, Mg, and Zn during 1999. The 2000 results were more typical of past years with significant amendment effects on soil pH and soil-test K, P, Mg, Ca, Zn, and CEC. The soil-test results cannot prove or eliminate the possibility that nutrient availability limited the response to the amendment program during 1999 or 2000, but they suggest that nutrients remained in good supply within the amended programs despite markedly reduced chemical fertilizer rates since 1996. The green manure rotation crop and supplemental irrigation treatments resulted in few changes in soil fertility.

Leaf samples collected at flowering during 1999 and 2000 showed that amendment applications tended to increase leaf Ca and B, while decreasing leaf Mg, P, Cu, and Mn. Amendments also increased leaf N during 1999 and decreased it during 2000. Effects on N, Ca, K, Mg, and Cu were small and all treatments were well within the sufficient range for potatoes (Westermann, 1993). Leaf Mn concentrations were highest in the NONE plots and all treatments had very high leaf Mn compared to published sufficient values. P levels were numerically quite similar over treatments. They were within the sufficient range during 2000, but in the marginal range during 1999. The amendment programs decreased leaf P concentration during 1999 and this may have limited the yield response to amendment. Leaf B levels were marginal in the NONE plots and in the sufficient range for all amended treatments during 1999. During 2000, leaf B levels were in the sufficient range for all treatments, but were significantly higher in AMEND than all other treatments. Based on the leaf analysis results it is unlikely that nutrient availability affected crop performance during 2000; however, enhanced B availability may have been advantageous for the amended treatments during 1999. Rotation and irrigation treatments had very few effects on leaf nutrient concentration during 1999 or 2000.

Experiment #2 — Crop Rotation Comparison and Residual Effects of Compost and Paper Mill Sludge. This study compared the following crop rotations: i) continuous potatoes; ii) two-year 1:1 potatoes-oats; iii) two-year 1:1 potatoes-vegetables; iv) three-year, potatoes-oats-timothy/clover; and v) amended two-year 1:1 potatoes-oats. The amended treatment was a measure of residual amendment effects. Compost (10 t A-1) and paper mill sludge (60 t A-1) had been applied during 1996. A detailed summary of the results is provided in the Appendix.

Results during 1999 documented positive residual effects (+41 cwt/A) of the 1996 amendment treatments; however, the amendment treatment did not significantly improve US#1 yields during 2000 (only +4 cwt/A compared to the reference). Tuber size and other quality attributes were not significantly affected by the amendment treatment during either year. Considering the entire four-year period, the US#1 potato yields were higher in the amended treatment (285 cwt/A) than the standard two-year rotation (264 cwt/A).

The three-year rotation significantly increased US#1 yields (+29 cwt/A) relative to the two-year potato-grain rotation during 2000, but not during 1999. Tuber size and other quality attributes were similar for the two- and three-year rotations. The four-year average US#1 yields for the rotation length comparison were 236, 264, and 277 cwt/A, respectively, for continuous, two-year, and three-year rotations.

Pre-tillage, soil bulk density was significantly affected by treatment during 1999, but not during 2000. In most comparisons, the amended treatment had lower soil bulk density than other treatments, but it was not lower than the three-year rotation. Soil water stable aggregate content (WSA) was significantly affected by treatment during both seasons. During 1999, the amendment treatment and the three-year rotation tended to increase WSA. During 2000, the WSA of the three-year rotation was greater than that of continuous potatoes, but the amendment treatment did not increase WSA relative to the standard two-year rotation. Soil carbon (%T-C) and Walkley-Black organic matter (%OM) were significantly increased by the amendment during both years. The three-year rotation was also beginning to have positive effects on %T-C and %OM. These soil analysis results suggest that amendment effects on soil properties were still present three to four years after treatment. The three-year rotation was significantly improving soil physical properties after only one rotation cycle and would be expected to have an increasingly important effects on soil properties as more rotation cycles took place. The advantages of the three-year rotation derive from the relatively high input of above- and below-ground clover/timothy and the fact that this crop is not tilled at all during the spring or summer.

Soil fertility analysis indicated that the rotation/amendment treatments significantly affected soil Ca, K, and Mg during both growing seasons. Soil P, Mn, Zn were also significantly affected during 1999 and soil pH and CEC were significantly affected during 2000. Soil Ca tended to be lowest in the continuous potato rotation, which also had decreased soil pH and CEC during 2000. The amended plots were relatively high in soil K and low in Mg; however, these differences are probably not very important to the results of the experiment, since all treatments tested quite high in both K and Mg. Soil-test P was highest in the amended plots during 1999; however, there were no significant differences during 2000. All treatments tested moderately high for available soil P during both years. During 1999, soil test Zn levels were significantly higher in the amended compared to the non-amended treatments.

Potato leaf and petiole tissues were analyzed to help determine if the observed crop responses might have been due to nutrients supplied by the rotation crop or amendment treatments. Based on these analyses, the 3-year rotation and the standard potato-oat rotation had significantly higher leaf N than the amended treatment and the continuous potato treatment. The three-year rotation had higher late-season petiole-N than the other treatments, indicating that it was better able to supply late-season N. This also indicates that yield advantages provided by the 3-year rotation may have partially been due to improved, late-season plant N uptake. Although the three-year rotation caused a few other significant changes in leaf nutrient content, the change in N status is the only one that was likely to influence yield.

The amendment treatment significantly affected the concentration of several nutrients in the leaves; however, most were within acceptable published ranges (Westermann, 1993), so it is unlikely that these changes affected yield. The amended treatment increased leaf K during 2000 and these concentrations were within the marginal range and could have contributed to observed yield differences. The amended treatment also significantly increased leaf B concentration during 2000 and numerically increased leaf boron concentration during 1999. Leaf B levels for most treatments were in the marginal range, while the B concentration in the amended plots was in the sufficient range. It is possible that some of the observed yield response to amendment was due to improved B fertility.

Objective 1b. UMCE’s Matt Williams and John Jemison continued their work with a group of Maine dairy and potato growers to identify the research needs concerning amendment, manure, and crop rotation use. Over the granting period, applied research was focused on efforts to show growers the importance of building soil organic matter. Over the past three years, we have conducted four applied research projects to evaluate alternative nutrient sources for potatoes. This work was primarily conducted on grower’s farms. Experiments were continued on the Donald Fitzpatrick Farm in Houlton, ME (a test of multiple rates of paper mill sludge vs. a control). Based on grower interest, a three-year study of liquid manure use on potato in central Maine was completed during 1999. Another trial evaluated solid dairy manure use on potatoes in a field with varying soil pH to assess the benefit and risk of this material in potato production. We conducted this trial on a pH-amended field in the summers of 1998 and 2000. The last trial that we conducted evaluated the use of paper fiber and composts as mulches on potatoes, and to try to boost the production of volunteer barley following harvest. While the paper fiber residual and composts did not increase potato yield during the first year, the ultimate impact may be seen in future years. Audiences at the March 13 and 14, 2000 soil health potato school talks in Houlton and Fort Kent, ME were used to obtain grower input for research and demonstration projects for the 2000 growing season. As a result, grower trials looking at extended crop rotations (Dan Corey Farm in Littleton, ME) and manure use on dwarf corn as a rotation crop for potatoes (Perry Lilley Farm in Smyrna, ME) were planned and conducted during 2000. Summaries from several of these applied research activities are presented in the Appendix. Information from these projects was delivered in various extension/outreach programs as described in Objective 1c and listed in Section 8 (publications and outreach).

Objective 1c. University of Maine Cooperative Extension educational activities on soil amendment use and crop rotations were conducted within several venues using partial support from this project. We focused our attention on doing educational programs that show growers the importance of building soil organic matter. We have done educational outreach on this project at the Maine Potato Conference (200 farmers), Rogers Farm field day (100 people), Aroostook Farm Tours and Field Days (80 people), Houlton Agricultural fair (1500 people), Southern Aroostook Soil Health Field Day (150 people), Winter Agricultural Seminars in Houlton and Fort Kent (200 people), Canadian Water Resource Association Regional Meeting, Grand Falls, New Brunswick (150 people) and the Northeast Potato Forum (85 people). Information generated from this has been used in articles on building soil organic matter in the Spudlines newsletter that goes to all Maine potato growers, papers delivered at the Maine potato conference, and other Maine potato educational programs. See Section 8 Publications/Outreach for a listing.

The last major outreach training effort was a regional Cooperative Extension / agency tour. On this tour, we took 18 people from New Hampshire, Vermont, and Maine on a tour of farms that were working very hard to maintain and build soil organic matter. We visited David Colson’s farm in Dresden Maine. It is an organic vegetable farm where he uses crop rotations and manure to both provide mineral nutrition for the crops and to build soils. The attendees had the chance to discuss different cropping ideas, and methods that he used to build soil organic matter. We visited Rob Johannson’s Farm in Goranson, Maine, and anther large sweet corn producer using zone tillage. We also visited a large animal composting operation where the attendees were able to learn how to do small scale large animal composting on farm, and then use the composting materials on the farm. On day two, we visited The Green Thumb potato operation in Western Maine. The farm manager gave us a tour of the operation and discussed ways they were using to build soil organic matter. It was a nice way to have the attendees see the difficulties larger operations face when trying to grow an organic matter decreasing crop like potatoes and be under the gun to be profitable. We also visited two organic dairy operations in Turner that were using some innovative approaches to build soil organic matter. One ran a large composting operation. The other was just trying to use as much cover cropping as possible and minimizing tillage as much as possible to do this. The final stop was a small flower and vegetable operation near Portland that was using cover crops to build soil. On the bus, we also showed videos on organic weed control methods, how to work with farmers to build soils, and other useful videos.

The attendees found the two-day tour to be very helpful in understanding what growers can do to build soil organic matter. They have told us that they have used much of what they learned on the tour in their daily jobs. All felt that they had a better understanding of how to work with growers to do a better job of building soil organic matter.

Objective 2. A rainfall simulator was used to measure the basic water infiltration rate (BIR) in field plots subjected to varying soil management. The BIR is the infiltration rate of a soil that has infiltrated water for a long period of time. It is the most stable estimate of infiltration rate. The runoff rate was also calculated as was sediment and nutrient load in the runoff. A more detailed summary of the results is presented in the Appendix.

The upper limit of the rainfall simulator test rate was 2.45 cm/hr during 1999 and 7.1 cm/hr during 2000. The 1999 rate was not high enough to reliably establish the early-season BIR, but it was high enough to establish the BIR during July/August, after time and rainfall events had changed the characteristics of the soil surface. In the July/August 1999 tests, the average BIR was 0.85 cm/hr and ranged from 0.44 to 1.65 cm/hr. In the June/July 2000 tests, the BIR ranged from 1.74 to 5.04 cm/hr and the average BIR of the amended plots was 3.71 cm/hr (SD = 0.91) while the average for the unamended plots was 3.48 cm/hr (SD = 1.29). No significant difference in BIR was found between amended and unamended plots during either year

The 200 % increase in rainfall intensity in 2000 more than doubled sediment concentrations compared to 1999. The sediment concentrations were not significantly different for amended versus non-amended treatments during either year. During 2000, when run off rates allowed a better test of erosion potential, the unamended plots had 50% higher sediment content than the amended plots.

The nitrogen concentrations in the runoff were not high; however, phosphorus concentrations were high enough to raise concerns. Dissolved phosphorus concentrations in the runoff filtrate were significantly higher from amended plots than non-amended plots during both year. In 1999, the amended plots average concentration was 0.44 mg/l and unamended plots averaged 0.28 mg/l. For 2000, the amended plots had an average dissolved phosphorus concentration of 0.38 mg/l while the unamended plots averaged 0.19 mg/l. Baker et al. (1978) proposed that the critical concentration of dissolved phosphorus that would lead to surface water eutrophication ranges from 0.01 to 0.03 mg/l depending on other characteristics of a target water body. Thus, the rain simulator results show that both amended and unamended potato field soils produce degrading levels of dissolved phosphorus in runoff and the organic matter amended potato plots pose the greatest risk.

The total nitrogen concentrations of runoff from the amended plots were significantly higher than those of the unamended plots during both years. Ammonium concentrations in the runoff filtrate were significantly different in 1999 and not significantly different in 2000. Nitrate concentrations were not significantly different between treatments in either year. There were no significant differences in sediment bio-available phosphorus between years or soil treatments.

The carbon, total nitrogen and bio-available phosphorus content of sediments were all significantly correlated to each other. The nitrate concentration in the runoff filtrate was negatively correlated with the nutrient concentrations of the sediments. Concentrations of other nutrients in the sediments and in the filtrate were not significantly correlated to sediment concentrations of the runoff.

Participation Summary

Education

Educational approach:

Activities and presentations included:

“Progress on potato management research.” Porter, G.A. Maine Potato Board research subcommittee. March 1999. Presque Isle, ME. (20 people attended)

“Use of liquid manure as an N source for potatoes” J. Jemison at the Northeast Branch of the American Society of Agronomy Meetings. (July 13, 1999; Guelph, Ontario, Canada, 40 people attended).

A soil health field day which demonstrated the impact of residuals and cover crops on soil properties (July 29, 1999; Houlton, ME; conducted in cooperation with the Southern Aroostook Soil & Water Conservation District, 168 people attended).

A field day demonstrating solid manure application on potatoes at the University of Maine’s Sustainable Agriculture Research Farm (Old Town, ME presented by John Jemison, 25 people attended).

A field day demonstrating liquid dairy manure application on potatoes at USDA-ARS research facility at Newport, ME (August 10, 1999; Newport, ME presented by John Jemison, 35 people attended).

A presentation summarizing University of Maine research on organic soil amendments (August 12, 1999; Grand Falls, New Brunswick, Canada; presented to the Canadian Water Resources Association (CWRA) by M.Williams, 100 people attended).

“Solid dairy manure as a nutrient source for potatoes” a presentation by J. Jemison at the UM Cooperative Extension Potato Conference (January 26, 2000; Caribou, ME; 100 people attended).

“Rotation cover crops” presentation by M. Williams at the UM Cooperative Extension Potato Conference (January 27, 2000; Caribou, ME; 100 people attended).

“Soil health, benefits of organic matter additions to soils, and use of cover crops” presentation by J. Jemison and M. Williams at the UM Cooperative Extension Potato Schools (March 13, 2000; Fort Kent, ME; 20 people attended);

“Cover crops, soil amendments, solid manure in potato production systems: benefits and management” presentation by J. Jemison and M. Williams at the UM Cooperative Extension Potato Schools (March 14, 2000; Houlton, ME; 25 people attended).

“Manure as an N source for potatoes: potential problems and benefits” a presentation by J. Jemison at the Northeast Potato Technology Forum (March 17, 2000; Bangor, ME, 70 people attended).

“Progress on potato management research.” Porter, G.A. Maine Potato Board research subcommittee. March 2000. Presque Isle, ME. (20 people attended)

“Progress on potato management research.” Porter, G.A. Maine Potato Board research subcommittee. March 8, 2001. Presque Isle, ME. (20 people attended).

“Potato crop and soil management research at Aroostook Research Farm” Porter, G.A.. Tour presented made to state legislators, industry members, and other agricultural leaders. July 20, 2001. Presque Isle, ME (40 people attended)

“Potato crop and soil management research at Aroostook Research Farm” Porter, G.A.. Tour presented made grower, industry members, and other agricultural leaders. August 15 2001. Presque Isle, ME (40 people attended)

“Maintaining and Building Soil Organic Matter” A Cooperative Extension regional agency training program and farm tour organized by J. Jemison, Summer 2001 (18 people from New Hampshire, Vermont, and Maine).

“The effect of potato mulches in dry years.” Jemison, J. Maine Potato Conference, January 23, 2002. Caribou, ME (100 people attended)

“Soil pH considerations using solid manure on potatoes”. Jemison, J. Maine Potato Conference, January 23, 2002. Caribou, ME (100 people attended)

“Potato yield response to soil amendments”. Porter, G.A. UMCE potato irrigation symposium. March 19, 2002. Caribou, ME (70 people attended).

“Changing soil carbon and nitrogen pools in intensively tilled rotations.” Griffin, T.S. and G.A. Porter. 2002. Annual Meeting of the American Society of Agronomy, November 10-14, 2002. (40 people attended)

Publications:

Jemison, J., T.S. Griffin, and C.W. Honeycutt. 1999. Liquid dairy manure as a nitrogen source for potatoes. Proceedings on the Northeast American Society of Agronomy meetings, July 1999 (abst).

Jemison, J., T.S. Griffin, and C.W. Honeycutt. 2000. Manure as an N source for potatoes: potential problems and benefits. Proceedings of the Northeast Potato Technology Forum, Bangor, ME. (abst)

Jemison, J., T. Griffin, and W., Honeycutt. 2000. Using liquid manure to meet the nitrogen needs of potatoes. UMCE Spudlines Newsletter. March 2000. Volume 38, No. 1.

Jemison, J. 2002. Toward sustainable irrigation for potato producers. UMCE Spudlines Newsletter. March 2002. Volume 40, No. 2.

Griffin, T.S. and G.A. Porter. 2002. Changing soil carbon and nitrogen pools in intensively tilled rotations. American Society of Agronomy Abstracts, November 10-14, 2002 (abst).

Jemison, J. 2002. The effect of potato mulches in dry years. Proceedings of the Maine Potato Conference. UM Cooperative Extension (abst.)

Jemison, J. 2002. Soil pH considerations using solid manure on potatoes. Proceedings of the Maine Potato Conference. UM Cooperative Extension (abst.)

Griffin, T.S. and G.A. Porter. 2003. Altering soil carbon and nitrogen stocks in intensively tilled two-year rotations. Biology and Fertility of Soils (in review).

Porter, G.A. 200_. Rotation length and organic amendment effects on soil properties and potato production. In preparation as a MAFES technical bulletin or article for the American Journal of Potato Research.

Porter, G.A. 200_. Residual and current-season effects of organic amendments and crop rotation on soil properties and potato production. In preparation as a MAFES technical bulletin or article for the American Journal of Potato Research.

Porter, G.A. 200_. Effects of supplemental irrigation, soil amendments, and crop rotation on soil properties and potato production. In preparation as a MAFES technical bulletin or article for the American Journal of Potato Research.

Weblinks (related to or containing output from the project):
http://www.umaine.edu/waterquality/Agriculture/potatograin2.htm

http://www.umaine.edu/waterquality/Agriculture/potatomanure.htm

http://www.umaine.edu/waterquality/Agriculture/fd_topic_99.htm

http://www.umaine.edu/waterquality/Agriculture/fieldday.htm

UMCE Fact Sheet on Soil Organic Matter Improvement in Potato Systems:

This fact sheet has been delayed because of: 1) delays in analyzing and summarizing the research results of this study; 2) slow integration of information from the applied experiments on growers farms; 3) uncertainties about the relationship between soil organic matter and potato diseases (e.g. powdery scab, a disease that has become increasingly of concern to potato growers in Maine). Given the powdery scab outbreaks in Maine during 1992, 1996, and 2000, we have been hesitant rush this Fact Sheet into print. It would be desirable to have a better understanding of how soil organic matter can be increased without aggravating powdery scab and other disease problems.

We hope to prepare this fact sheet as the information from this project comes together and as we have more opportunity to interact with plant pathologists regarding the soil-borne disease issues.

Project Outcomes

Impacts of Results/Outcomes

This research and extension project developed new information on crop, soil, nutrient, and economic effects of soil amendments and crop rotations for potato production systems. This new information will be critical as growers make decisions about soil management in future years. It will help farmers make good decisions on the adoption of longer crop rotations, manure use, and the use of composts/paper mill sludge. Education and outreach efforts were used to raise farmer, industry, Extension, agency, and general public awareness of soil organic matter management, benefits, and concerns on potato and other farms.

More than 18 presentations have been made so far using information from this project. These presentations resulted in an estimated audience contact of about 1100 (which we would further estimate as split roughly 45% farmers and 55% professional, industry, Extension, and agency contacts). Information was made available to an additional 1500 people, mostly the general public, at the Houlton agricultural fair. Two articles were published so far in UMCE’s Spudlines which has a circulation of 768 (approximately 400 growers). Many additional contacts have occurred through the other published outputs and web site listings described in the Publications and Outreach section

Economic Analysis

The research station experiments in this project studied three major management approaches which were expected to affect soil organic matter and crop productivity in a potato production system. These were: 1) a set of long-term and shorter-term amendment treatments involving a combination of compost and manure; 2) residual effects of a single-year season treatment using compost and paper mill sludge; and 3) extending the crop rotation from a two-year, potato-oat system to a three-year, potato-oat-green manure system. Pertial budgeting approaches were used to analyze the economic effects of each change. Details are provided in the Appendix.

The basic economic analysis using a conservative potato price of $6.17 per cwt and annual applications of manure (20 t/A) and more expensive compost (10 t/A) shows that the amended program (AMEND) for non-irrigated potatoes is slightly less desirable (-$5.54/A/year over an 8-year study period) than the standard system (NONE). AMEND becomes even less desirable relative to NONE in an irrigated system (-$27.91/A/year over an 8-year period). In either case, amendments provided a positive US#1 yield benefit (40.1 and 36.5 cwt/A, respectively) and substantial fertilizer savings; however, these benefits were overshadowed by the high annual purchase and delivery cost of the amendments [compost ($150/A/year) and manure ($100/A/year)]. Increasing the value of the potato crop to (e.g. to $7.50/cwt) results in a favorable bottom line (e.g. +$ 47.82/A/year over an 8-year study period for the non-irrigated plots) as does reducing the cost of the amendment program.

Suspending the amendment program after four years and relying on residual amendment effects (SASP) for the remaining years reduced the cost of the amendment program and proved to be profitable relative to NONE (+$81.06/A/year over an 8-year study period). A single year of amendment application (ONCE) followed by reliance on residual amendment effects for the remaining years reduced the cost of the amendment program by about 88% and was quite profitable relative to NONE (+$80.52/A/year over the 5-year study period). Increasing the potato price and/or reducing the cost of the amendments would further increase the relative profitability.

The base analysis of the single-year application of compost (10 tons/A) and paper mill sludge (60 tons/A) to non-irrigated potatoes grown in a two-year rotation shows that this program is slightly more profitable that the non-amended program (+$6.91/A/year or $2074/year for a 300-acre farm). The key factors in this analysis are the cost of the amendments and the value of the potato yield increase. The relative profitability of the amendment program would increase if the price of the compost decreased or if the potato price increased. On the other hand, the amended system would become relatively less profitable if the paper mill sludge becomes a purchased input (for this study it was delivered free-of-charge by the waste generator).

Using the base price of potatoes ($6.17/cwt) and setting the number of potato acres to a constant value (e.g. 150 acres), the three-year rotation returns an additional +$54.71 per acre of potato production ($8,206 to a farm growing 150 acres of potatoes), so expanding the land base to accommodate this rotation makes sense if the annual cost of leasing (or ownership) and transportation was less than $54.71/A. Expanding the land-base becomes more economically favorable if the potato price increases (e.g. to $7.50/cwt). It would also be favored if the yield response to the three-year rotation was greater than that reported in this study (13 cwt/A based on the first cycle through a three-year rotation). Due to the nature of crop rotation effects, we would expect that the advantage attributed to the three-year rotation would expand over time and that this would provide further incentive to expand the land base and lengthen the crop rotation.

Farmer Adoption

This research and extension project will help farmers make good decisions on the adoption of longer crop rotations, manure use, and the use of composts/paper mill sludge. Soil improvement remains an important priority area for the Maine Potato Industry (see Appendix for Maine Potato Industry research priorities). Although we did not collect formal survey data on adoption of these practices, discussions with growers lead us to conclude that adoption has not changed much over the past five years. Many growers are open to the idea of placing a portion of their acreage into a three-year rotation. The data from this project and subsequent years of research should help growers with this adoption decision.

A small group of growers remains committed to the use of organic amendments (manures, composts, and sludges) to increase soil organic matter and decrease their fertilizer bills. From discussions with growers, the three major impediments to farmer adoption of manure, compost, and sludge use in Maine are: 1) proximity and availability of the amendments; 2) uncertainty concerning the yield response, economics, and nutrient availability relative to the known performance of chemical fertilizers; and 3) concerns about soil-borne disease during wet growing seasons. This project has helped address Item #2; however, the latter concern has been growing as a result of powdery scab and pink rot problems over the past decade.

Areas needing additional study

Three critical areas needing further information, research, or action are: 1) Increasing the availability of organic amendments, such as manure, sludge, and compost, in our area and getting better information on what the production and transport costs of these materials would be; 2) Better information on soil amendment affects on soil-borne disease and how to better manage those diseases that tend to become more prevalent as soil organic matter content increases; and 3) Better information on the long-term effects of extended crop rotations (this study looked at only one rotation cycle and the full set of benefits may take several cycles to fully develop).

Finally, this research documents the yield advantages that can be provided by soil amendments and longer crop rotations in potato systems. The nature of this response is complicated. How much is due to effects on soil biology, nutrient supply, soil moisture changes, or other soil physical properties? Wise use of these management tools would be fostered by better answers to these questions.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.