Note to readers, attached is the complete final report for FNE96-127
Mr. Fitzpatrick experimented with composted paper mill residue as a mulch and soil amendment on his potato farm. He expected that application of a thick carpet of this material would lead to three results in particular: 1) improved weed control, 2) better soil aggregation, and 3) darkening, and consequent warming, of the soil. He used a modified lime spreader to apply the compost to four plots on his farm, at the rate of 10 tons of dry matter per acre, and he kept four other plots as controls. The mulch was applied as the potato seedlings began to emerge. Control and mulched plots were both treated with Gramoxone, for weeds, just prior to emergence; later the control plots also received a treatment of Sencor herbicide. The control plots were hilled twice, and the mulched plots once.
Canopy closure, which tends to proceed faster when there are fewer weeds, appeared to be slightly better in the mulched plots; though whether the mulch had anything to do with this is dubious, since both treatments and controls experienced only slight weed pressure this year. The treatment had little or no effect on yields, which averaged around 12.4 tons per acre; similarly little effect was observed on tuber set.
Mr. Fitzpatrick remarks that this was an exceptionally rainy summer. Petiole nitrate levels were extremely low, possibly because the rain washed mineralized nitrogen out of the soil. Low levels of plant-available nitrogen may have stunted plant growth, and thus confounded the treatment effects.
Though the compost of paper mill residue would not appear to have produced the desired effects, Mr. Fitzpatrick still has faith in its potential, and means to try the experiment again. Certainly any effects it has on the soil will likely be gradual, and perhaps not discernible for many years.