Use of Short Paper Fiber Residuals as Soil Conditioners 

John Jemison and Chris Reberg-Horton, University of Maine Cooperative Extension Water Quality and Sustainable Agriculture Specialists

Executive Summary

Short paper fiber residuals (SPF), a by-product of the pulping process used in paper production, are excellent materials for soil amendment. The high carbon content of SPF can lead to improved soil physical properties, plant water availability, and crop yields. These materials have been evaluated in a number of different trials in Maine and in other states as soil conditioners, surface mulches, and liming agents. While beneficial in a number of different cropping systems, the potential benefits are particularly high in potato rotations due to the intensive production methods and the low organic matter content of these soils. When used at high application rates as a soil conditioner, Williams and Griffin (1997) found approximately 20 percent higher yields in the first year of potatoes following application, and 11 percent higher than the untreated plots in the second potato cycle. When used as a surface mulch, we found significantly higher amounts of water in the soil at each sampling date indicating that the material does reduce evaporative loss. This increased water led to significantly higher marketable potato yield in 2002. Some SPF materials also have the capacity to be used as liming agents. In this case, SPF can improve soil physical properties and increase soil pH. Used in 2003 as a liming agent in corn, SPF was found to increase soil pH from 0.2 – 0.5 pH units, which in-turn likely increased soil nutrient availability and improved conditions for weed control.

Introduction

Potato growers are increasingly interested in management measures that ensure production consistency.  Weather patterns are variable year to year, but long-term weather trends are tending toward drier weather patterns. Over the past century, average rainfall has dropped between 4.8 and 8.7 inches in the southern interior and northern Maine climatic zones, respectively (Zielinski and Keim, 2003). Climatic predictions for the future suggest warmer and drier summers. Potato growers should consider using management methods that improve utilization of natural precipitation as well as irrigation. There is insufficient water in the state for all potato growers to irrigate. As well, irrigation systems can be expensive, water sources are less than reliable, and sometimes irrigation is not favorable. So, it is very important to look at alternative methods to increase plant available water.

Evaluation of various materials to improve soil condition

Over the past several years, we have studied the effect of improving soils through a number of management measures that do not rely on irrigation: longer crop rotations, use of solid and liquid manure to build soils, and the use of compost and paper fiber residuals. Each of these methods has provided varying degrees of benefit to the subsequent potato crops.

Crop rotation

Longer crop rotations (more years between potato crops) have been a solid method to improve potato yield and quality. Potato production requires much soil mixing which can causes soil organic matter to decline. Since potatoes are the most financially valuable crop, most growers choose to maintain a 1:1 rotation of potatoes and grain. 

Use of manures

Use of solid and liquid manure has proved to be a safe and reliable source of nitrogen for potatoes (Jemison et al., 2000). Despite demonstrating that pathogen levels were not increased by using manure, growers have been reluctant to use manure on potatoes.   

Use of Short Paper Fiber Residuals as Soil Conditioners

Use of short paper fiber (SPF) residuals has led to improved soil quality in potato systems (Gagnon et al., 2001; Zibilski, 2000). A by-product of the pulping process used in paper production, SPF consists of paper fibers of insufficient strength or length to be reused.  SPF also contains clay fillers and coatings rinsed out in the pulp manufacturing process. Three possible ways to use SPF include incorporating SPF in the fall as a soil conditioner, as a mulch, and as a liming agent depending on the source. Williams and Griffin (1997) evaluated two rates of SPF as a soil conditioner in a small grain-potato rotation. Yield from the first potato harvest (1994) increased from 230 to 278 cwt/ac, and in the second cycle of potatoes (1996) from 258 to 290 cwt/ac from a single addition of 20 dry tons SPF/ac. They also documented improved soil physical properties and soil water availability.

Use of Short Paper Fiber Residuals as Mulches

We recently evaluated SPF as a mulch on Yukon Gold potatoes at the Rogers Farm in Stillwater, ME. As a mulch, SPF should help hold soil moisture in the growing season by reducing evaporation, and potentially building soil organic matter after incorporating SPF into the soil at harvest. We evaluated the use of compost and SPF mulches applied after the final hilling to hold soil moisture. We hand applied 7.5 and 15 dry tons/ac of SPF and compost to four row potato plots. Total and plant available water was assessed at weekly intervals in 2002.  Potato yield and quality was determined at harvest.  In 2003, we assessed the impact of residual SPF and compost mulches incorporated in the plots from the 2001 season.