Potato - Grain Study (2001)

John Jemison and Matt Williams

Background

The overall purpose of this study is to examine ways to protect soils from erosion and to examine cost effective ways to build soil organic matter. This study is actually two studies combined in one field plot: a volunteer barley regrowth trial and a potato mulch study. Potato followed by barley is the most common 1:1 rotation for potato growers in Maine. When barley is harvested, some amount of barley seed falls back on the soil surface and will likely germinate and grow prior to frost. We are interested in learning how much we can influence volunteer barley regrowth before freezing. Can we add nitrogen fertilizer to boost growth and significantly influence the amount of biomass being returned to the soil? 

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 the effect of added N to volunteer barley biomass before frost

• Determine effect of added compost mulches on yield and quality of potatoes

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 blocks 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 left 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 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 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 there was some scab and rhizoctonia on the potatoes, it was not sufficient to hurt overall potato quality. 

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 and 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

To date, we have found some scattered barley regrowth in the harvested barley plots. However, there are no discernable trends as yet.