Effects of mulches on soil properties and tomato production II. Plant-available nitrogen, organic matter input, and tilth-related properties

Potential contributions several mulches to soil organic matter (OM), and their effects on crop-available nitrogen (N), earthworm activity and tilth-related soil properties, were evaluated on five working vegetable farms in Virginia. A 100-mm thick hay mulch added sufficient organic carbon (C) and N to replace seasonal soil OM losses expected for temperate zone soils. Paper and plastic mulches contributed little or no OM, but mulching alleys between film-mulched beds helped replenish soil OM in these mulching systems. At one site, soil NO3-N was higher under plastic and oiled-paper mulches than under organic mulches or without mulch, probably because plastic and oiled paper reduced leaching of NO3-N. Mulch treatment did not affect soil NO3-N at other sites, and generally did not affect tomato foliar TKN, except when the treatment reduced soil moisture levels. Hay and compost mulches had C:N ratios ranging from 24 to 48, but high foliar TKN in these treatments indicated that the mulches did not reduce N availability to the crop. Mulch treatments imposed for a single growing season did not affect soil bulk density, steady state water infiltration rate or wet aggregate stability. However, earthworm populations at the end of the season were about twice as high under hay mulch as under black plastic.