Nitrogen fertilizer, manure, and compost effects on weed growth and competition with spring wheat

Crop fertilization is an important component of integrated weed management systems. A field experiment was conducted to determine the effect of various application timing-tillage intensities and N sources on weed growth and spring wheat (Triticum aestivum L.) yield. Timingtillage treatments consisted of applying the various N sources in either the previous fall or in spring each under zero-till or tilled conditions. Nitrogen sources consisted of granular ammonium nitrate fertilizer applied either surface broadcast or subsurface banded 10 cm deep between every second wheat row, fresh cattle (Bos taurus) manure, and composted cattle manure. An unfertilized control also was included. Treatments were applied in four consecutive years to determine annual and cumulative effects. Subsurface-banded N compared with broadcast N fertilizer often reduced N uptake by weeds, decreased weed biomass, and increased wheat yield. Weed N uptake and growth with fresh and composted manure tended to be intermediary between banded and broadcast N fertilizer in the initial year but was similar to or greater than that with broadcast N fertilizer in subsequent years. The gradual N release from manure and compost over years appeared to benefit weeds more than spring wheat. The ranking of the weed seedbank at the conclusion of the 4-yr experiment was composted manure = fresh manure >= broadcast N fertilizer > banded N fertilizer. Information gained in this study will be utilized to develop more efficient fertilization strategies as components of integrated weed management programs in spring wheat production systems.