The growing interest in sustainable local food production has created incentives for crop producers, especially in urban areas, to grow food for local consumption using low-cost, renewable materials and/or organic production techniques (Butler and Maronek, 2002; Lorenz and Lal, 2009; McCullum et al., 2005; Organic Trade Association, 2011). Alternative, low-cost weed management strategies are appealing in urban environments because of the close proximity of crop production to people, which may preclude the use of pesticides, or the use of mechanical tillage because of a lack of space or financial resources for equipment and skilled labor. The recycling of urban wastes such as paper and plant trimmings for weed suppression in urban farms could potentially represent an inexpensive and renewable alternative to herbicides, tillage, and hand weeding.
Beginning with their commercial introduction in the 1960s, plastic film mulches coupled with drip irrigation have played a major role in increasing yields of several vegetable crops (Kasirajan and Ngouajio, 2012). Black polyethylene plastic conserves soil moisture and is impervious to light and rainfall, making it effective at controlling weeds but conducive to excessive water runoff (Feeser et al., 2014). Polyethylene mulch in tomato plots resulted in two to four times more water runoff and six to 19 times more pesticide runoff than plots mulched with hairy vetch (Vicia villosa) residues (Rice et al., 2001). Black plastic mulch can also cause heat stress in some crops during hot weather (Gruda, 2008). Another major disadvantage of using nonbiodegradable polyethylene plastic mulches is that they require annual removal and proper disposal (Díaz-Pérez and Batal, 2002). Using black plastic mulch costs U.S. vegetable growers up to $750/ha every year, which generates 112–135 kg·ha−1 waste plastic with an added disposal cost of ≈$50/ha (Feeser et al., 2014).
Various biodegradable materials, including starch or cellulose-based bioplastic films and biofabrics, have been tested as alternatives to plastic mulch with varying results depending on crop, mulch material, and environmental factors (Kasirajan and Ngouajio, 2012; Miles et al., 2012; Wortman et al., 2015). Newspaper mulch is an alternative to nonbiodegradable plastic, but it can be prone to fragmentation on the soil surface and degrade too rapidly to provide a sufficient period of weed suppression (Schonbeck, 1999; Shogren, 2000). Several researchers have investigated that paper treated or mixed with various substances intended to delay biodegradation and/or enhance weed suppression, but results have been variable (Anderson et al., 1995; Shogren, 2000; Shogren and David, 2006).
An important factor affecting the efficacy of newspaper-based mulches for weed suppression is the fragment size of the paper when applied (e.g., shredded vs. sheets), and several studies have demonstrated that shredded newspaper mulches suppressed weeds and resulted in crop yields comparable to those provided by black plastic mulch (Grassbaugh et al., 2004; Laurie et al., 2014; Pellet and Heleba, 1995) or a hand-weeded control with no mulch (Sanchez et al., 2008). In a study where shredded newspaper was applied at a thickness of 10 or 15 cm, weed germination was suppressed for two seasons without any negative effect on two of the three nursery crops studied (Pellett and Heleba, 1995). Shredded newspaper provided comparable weed suppression to black plastic in tomato (Grassbaugh et al., 2004), and increased yields of sweet corn, soybeans, and tomato were achieved using shredded paper mulch compared with straw mulch or bare ground (Munn, 1992). In contrast, ground newspaper mulch (particle size ≈0.1 cm2) resulted in collard yield lower than or equivalent to bare soil, and collard tissue nitrogen (N) concentration lower than under bare soil, black plastic, or wood chip mulch (Guertal and Edwards, 1996). Chopped newspaper (5 × 5 cm squares applied at a 7.6-cm thickness) controlled weeds in tomato more consistently than 12.7-cm-thick shredded newspaper (1 cm by 60 to 75 cm long strips) or 15.2-cm-thick wheat straw mulch, and also provided greater weed suppression than black plastic or plastic landscape fabric (Monks et al., 1997).
Recycled newsprint is a resource available in large quantities, especially in and around urban centers (Paper Industry Association Council, 2007). In the past, there was concern about the environmental impact of some newspaper inks that contained polycyclic aromatic hydrocarbons (PAHs) of environmental and health concern; however, by the mid-1990s, most newspapers switched to soy-based ink that does not contain PAHs (Anderson et al., 1995). Application of newsprint as a mulch is acceptable under organic certification as long as the newsprint is not contaminated with glossy advertising pages or colored inks (USDA, 2008).
One challenge with using paper as a mulch material is soil N immobilization. Noncomposted, recycled paper products have a high C:N ratio (≈500:1) that upon decomposition can result in a depletion of plant-available soil N (Edwards, 1997; Glenn et al., 2000; Tahboub and Lindemann, 2007). Combining paper with plant residues having a lower C:N ratio can reduce immobilization of inorganic N in the soil. In addition to providing supplemental N, plant residues and other organic materials can increase soil organic carbon and improve soil structure and quality (Saroa and Lal, 2003). Plant residues used as mulch materials have included grass clippings, straw of various cereal grains, wood fiber chipped from downed trees, and municipal leaf waste (Duppong et al., 2004). However, biological residues vary widely in N content and bioavailability. Fresh grass clippings represent a plant residue that can be comparatively high in bioavailable N and a potential resource in urban environments (Fang et al., 2007).
Plant residue may be less effective than plastic film as mulch for weed control because it often does not maintain a continuous barrier, and some areas of the soil surface can be left exposed due to residue decomposition or displacement by wind or water. Shredded newspaper becomes cohesive after being wetted by rainfall or overhead irrigation, reducing potential gaps between fragments (Grassbaugh et al., 2004). Combining shredded newspaper with plant residues such as grass clippings may offset the loss in weed control caused by gaps between grass fragments while also offsetting the high C:N ratio of paper.
The objective of this study was to compare the effects of shredded newspaper, NP + grass, woodchips, black plastic, and bare soil on weeds, insects, soil moisture, and soil temperature in pumpkin production.
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