Cottonseed and Canola Meal as Organic Fertilizers for Landscape Plants

Plants need large amounts of nitrogen (N) and other nutrients for proper growth and development. Essential nutrients can be supplied by various sources including organic fertilizers. This study was conducted to determine the effect of using cottonseed and canola meals as organic fertilizers on the growth and ornamental quality of landscape plants. This information can help identify alternative organic fertilizer sources and dispose of excess meal. The effects of incorporating or topdressing with cottonseed meal with or without soapstock, canola meal without soapstock, urea, or no amendment (control) were investigated using plants of marigold (Tagetes erecta ‘Inca II Gold’) and Redbud (Cercis canadensis) in a Norge loam (fine-silty, mixed, thermic Udic Paleustolls) at Stillwater, OK. Fertilizers were applied at a rate based on standard N recommendations for landscape plants (4.9 g.m⁻² N) in May 2008. In each plot, two redbud seedlings were planted 1.5 m apart or four marigold plants were planted 30 cm apart. A buffer zone was left between the end of each plot and the plants, and polyethylene edging was installed between plots to reduce movement of nutrients. Each treatment was replicated 10 times for each species. Plants were measured at planting in May and again in July. Soil samples were collected prior to treatment application and in August for elemental analysis. Leaf samples were collected in August for elemental analysis. Few differences occurred among fertilizer sources and between application methods within fertilizer source for either species. Between May and July, redbud trees receiving incorporated urea grew more in height and caliper than those topdressed with urea. Redbuds receiving urea as a topdress treatment increased in caliper more than those receiving incorporated urea. Redbuds receiving cottonseed meal with soapstock incorporated had greater increases in caliper than with cottonseed meal as a topdress. No differences in redbud leaf elemental content occurred. For marigolds, height increased more in control plots than in plots receiving incorporated cottonseed meal with soapstock. Differences in leaf calcium, sulfur, nickel, and total N content occurred in marigolds. No difference in soil nutrient content occurred among fertilizer treatments for either redbuds or marigolds. Cottonseed and canola meal would be expected to release nutrients slowly, thus treatment differences may be more apparent during the 2009 growing season. Results indicate that canola and cottonseed meals provide sufficient N for the growth of landscape plants.