Potato - Grain Study (2002)

The second part of the study examines a different way to increase soil organic matter. With the multiple soil disturbances during the production year and the minimal amount of biomass that is returned to the soil, potato production over time will lower soil organic matter. This makes the plants more susceptible to water stress, disease, and potentially lower yields. We have explored many ways to add carbon to these production systems to reduce this potential problem. In this project, we are evaluating paper mill and compost mulches applied at last hilling to see the effect on potato growth and yield. These composts may help hold water and reduce weed growth in potatoes.

Study Objectives

• Determine effect of added compost mulches on N status, growth, yield and quality of potatoes

• Determine the effect of added N to volunteer barley biomass before frost

Methods

A randomized complete block experiment with six replications was established during the summer of 2001. “Robust” barley was planted on 8 May 2001 at a rate of 120 lbs/ac. “Yukon Gold” potatoes were planted on the same day next to barley in strips.  The size of each major block was 200 feet long; the potato plots were 11.3 feet wide and the barley plots were 8 feet wide. We applied 80 lb/ac N, 40 P₂0₅ and 60 K₂0 at planting in the barley trial. Barley was sprayed with 2,4-D at 1 pt/ac in June.  In the barley study, no treatments were applied until after harvest (13 August 2001). Following harvest, each major block was split into five subplots. Five rates of N (0 – 40 lb N/ac in 10 lb increments) were hand applied over the barley stubble on August 16. In the potato study, compost and papermill sludge was hand applied at 7 and 15 dry tons/ac on July 5, 2001. A check plot was included to assess the impact of the cover materials. Upon delivery to the field site, paper fiber and compost was tested to have a dry matter content of 30 and 46% respectively. We tested soil water content twice, at two week intervals, by taking gravimetric water to a depth of 6 inches. Soil temperature was collected twice using a standard soil thermometer.  We tested N status using a hand-held chlorophyll meter. Potatoes were harvested by hand on 23 August 2001. Potatoes were graded and 20 marketable potatoes were rated for quality by estimating percent surface area covered by common scab and rhizoctonia. 

Results - Potatoes

Compost and paper fiber mulch had no significant impact on soil moisture, temperature, yield or quality of potatoes in 2001. Soil moisture was found to be somewhat higher due to the presence of compost and paper fiber. A trend toward higher soil moistures was found with the higher rates of each particularly after the last measurement, but this difference was not statistically significant (Table 1). Temperature was not significantly affected by the presence of mulch or compost in this study as well.

Table 1.  Soil moisture and temperatures after application of mulch materials

Overall, potato yield was lower than average due to drought (Table 2).  While tuber size was fairly good, tuber number was quite low. Tuber number was set by the plant prior to application of compost or paper fiber. Yield was decreased by the presence of compost and paper fiber at the highest rate by 13 and 15 cwt/ac, respectively. This may have been due to the paper fiber and compost tying up what little rain fell on the plots after the application of compost. While the soil moistures were not significantly different due to the presence of mulches, they may have had a more subtle impact on soil water relations than our method of soil moisture analysis allowed us to detect. Leaf chlorophyll data indicate very little tie up of nitrogen from the presence of the mulch. 

Table 2. Yield and quality of potatoes harvest 8/23/01.

Lastly, potato quality was not hurt by the presence of mulch and fiber (Table 2). While some scab was found on the potatoes, it was not sufficient to hurt overall potato quality, and it was not influenced by treatments. Rhizoctonia was influenced by treatments with the highest compost rate apparently producing slightly higher amounts of rhizoctonia. Although statistically significant, this amount of rhizoctonia would not affect marketability. 

Conclusions

To date, there is no apparent beneficial or detrimental effect on the presence of compost or paper fiber residual mulches applied to the soil surface following the second (final) hilling operation.  If data from past trials holds true here, the benefit may be found when potatoes are planted where the compost and fiber will be tilled in – this being in the 2003 growing season. 

Thus, what we find from this work is that applying paper fiber and compost mulches after last hilling may be a useful time to apply the materials (due to work load) and it doesn’t significantly hurt potato production. 

Results - Barley

In October following killing frost, we sampled the barley for total biomass as influenced by the N rates applied. We took two samples per plot, separated the samples into components:  barley and weeds.

The barley regrowth was somewhat spotty. As a result, while the applied N increased barley biomass, the difference was not statistically significant. At the highest N rates (30 and 40 lbs N/ac), both barley and weed biomass were increased by the addition of N. From this first year of work, we found that 30 – 40 lbs N/ac bought the grower an additional 850 – 900 lbs of dry matter incorporated into the soil in the spring.  While there may be other ways to increase soil organic matter, over the long term, this could be quite beneficial.  We found this despite poor growing conditions.

Table 3. Volunteer barley regrowth as influenced by applied N.

Study #2. Influence of Soil pH and Solid Dairy Manure on Potato Yield and Quality.

This study was stimulated by a Sustainable Agriculture Working Group discussing issues related to integrating crop and livestock production systems.  This group, made up of Extension, farmers, and industry staff, has been discussing problems and concerns about integrating crop and livestock systems.  We initiated this demonstration to evaluate the effect of solid dairy manure used as a nutrient source on potato disease complexes as a function of soil pH.  Producers often produce potatoes at a very low pH to avoid scab and other potato diseases.  There may be cases where this is beneficial, but it limits rotation crop options.  We wanted to use this area because soil pH ranges from 5.0 to 7.0. 

Project Goals

• Determine if solid manure will increase the likelihood of potato diseases

• Assess the impact of soil pH to affect disease suppression 

• Assess potato growth, development, and yield as a function of manure or fertilizer N

Treatment Combinations

In this study, we evaluate several combinations:

• For the main plot, manure was applied at 24 tons/ac of solid dairy manure. 

• Non-manured potatoes received 1400 lbs/ac 10/10/10 fertilizer in a band at planting.

• Soil pH varied across strips from pH 4.8 to pH 7.0.

Data Collected

We collected leaf chlorophyll measurements and leaf petioles at 35 and 50 days after planting. Stem counts were taken to assess the impact of pH on rhizoctonia activity and shoot length measurements were taken at 40 and 55 days after planting to assess potential for yield and potato development. At harvest, we dug 20 foot row segments to obtain yield estimates. We rated percentage of scab and rhizoctonia on 25 US #1 potatoes from each plot area.   

Results 

Potato growth and development were not strongly influenced by soil pH or nutrient source. Looking at 2-year averages, at 35 days after planting (DAP), stem count (numbers of stems emerging from the ground) was not influenced by nutrient source or soil pH. This suggests that rhizoctonia activity is not affected by soil pH or nutrient source in this study, and is not significantly influencing the number of potato shoots coming out of the ground. There was some influence of nutrient source and soil pH on stem length.  Generally, at the lowest soil pH, there was a significant reduction in size of plant. This difference was nullified over the other soil pH range.  

The 2-year average leaf chlorophyll at 35 DAP was higher with fertilizer-N as the nutrient source (52.7 spad units for the fertilized plots vs. 49.7 for the manured plots). One possible explaination for this is that there is less N is immediately available to the potatoes in the manured plots, and so the plants are slightly N deficient. In both years, temperatures were warmer than average, and this early difference was not found later in plant development suggesting that the difference in N availability is very short term.

Over the two years, manure did seem to provide some yield benefit to the potatoes, likely because of improved water holding capacity in the soil. Over the two years, we found a 17 cwt/ac difference in the manured vs. fertilized plots. This difference was statistically different at the 10% level of confidence.  Another important finding was that manure applied to lower pH soils appeared to greatly improve yield over using fertilizer-N (Figure 1.) It is hard to tell whether the organic matter associated with the manure is minimizing some of the negative effect of the low acidity on plant growth and development, or if another factor is causing this difference. But, the effect was significant. 

Disease was significantly influenced by soil pH and nutrient source over the two growing seasons.  We found significantly less scab at lower soil pH than at higher soil pH across both nutrient sources, and there was a much higher percentage of scab free potatoes in the non-manured potatoes than in the manured potatoes (66% in non-manured potatoes vs. 44% in the manured potatoes).  If you want to keep potatoes with less than 5% surface area affected by scab, one can produce potatoes at pH 6.0 and not use manure or produce potatoes at pH 5.5 and use either nutrient source.  There was a significant increase in percent surface area affected by scab at pH 6.0 with manure (Figure 2).

Lessons Learned

• Potatoes appear to grow well with manure-N sources

• Rhizoctonia was not apparently increased with manure because shoot numbers coming out of the ground were similar.

• Yields were higher in manured plots than non-manured plots. 

• Scab is a real concern with solid manure at higher soil pHs with scab susceptible Yukon Gold potatoes. Scab was significantly influenced by soil pH and nutrient source.

• If you want to use solid manure, you may need to maintain soil pH close to 5.5 to avoid scab issues which will have an influence on crop rotation schemes.

Study #3. Cover crops in soybean production

This study was doomed from the start due to the strange environmental conditions found in 2001. We intended to conduct a study to evaluate different ways and times to establish cover crops in soybeans. The goals of the study were to 1) evaluate whether typical potato herbicide programs would prohibit early season planting of small grain or annual ryegrass cover crops; 2) assess benefits of increased biomass by early establishment; 3) assess difference in N contribution to a subsequent potato crop by harvesting soybeans for forage or for beans. 

The study was planted on June 1, 2001. The soil was very dry and emergence was slow. What I didn’t realize was that the soybeans were planted deeper than it was anticipated. It did not rain for over a week and nothing emerged. Finally we had enough rain to stimulate germination. By the time we realized that the plants were not going to emerge, three weeks had passed. We took another field and planted the soybeans on 6/21/2001. Again, emergence was very slow in soybeans. We packed the field to ensure that we would not plant the beans too deep. We applied the various treatments to the field, but the beans were frosted before we could harvest them for silage. So we would have had no difference between harvests to address goals 2 or 3. The only thing we can safely assume is that from the good stand found with both annual ryegrass and barley, we found that a standard herbicide program is not going to affect early germination of cover crops. I regret that we were not better able to address these questions.