Effect of Potato Mulches in Dry Years

John Jemison and Matt Williams, University of Maine Cooperative Extension

Potato growers are becoming increasingly interested in irrigation. However, potato growers frequently need moisture when surface waters are being taxed the hardest. Groundwater systems can be quite expensive.  So, it is very important to look at alternative methods of increasing plant available water without having to rely on irrigation. Thus, the objective of this study was to determine effect of added compost mulches on yield and quality of potatoes.

In this study, we have evaluated the use of compost and paper fiber residual (PFR) mulches applied after the final hilling to hold soil moisture. The study was set up as a randomized complete block experiment with six replications. Compost and PFR were hand-applied at 7.5 and 15 tons dry matter/A following the final hilling. 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. Potato yield was measured by harvesting one 20-foort row of potatoes from each plot. Potato quality was assessed by estimating surface area of scab and rhizoctonia. 

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/A, 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 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 real 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. If these materials are applied somewhat sooner and when there is more soil moisture in the ground, they may do a nice job to protect soil moisture and show a greater benefit. This work will be repeated in 2002.