UREA PLACEMENT AND NITRIFICATION INHIBITOR EFFECTS ON GROWTH AND NITROGEN ACCUMULATION BY NO-TILL WINTER WHEAT

Authors: RAO, SRINIVAS; POPHAM, THOMAS

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Conservation production systems continue to increase as an alternative system for reducing soil erosion and conserve soil water. However, lower yields due to greater immobilization, denitrification, and leaching have been reported as reasons for poor performance of surface applied N with conservation tillage practices. Nitrification inhibitors have shown to be effective in reducing these losses under conventional tilled soils. Field studies were conducted at El Reno, OK, to determine the effectiveness of two nitrification inhibitors (nitrapyrin and DCD-N) and their placement (broadcast and banded below seed) effect on aerial dry matter accumulation as well as uptake and redistribution of applied N among plant parts under no-till winter wheat production system. Results indicated that neither inhibitor significantly affected total dry matter accumulation, but there was a significant response from nitrification inhibitor, DCD, which was most effective in increasing N content when environmental conditions were favorable for leaching. Cooler temperatures and wet conditions in early spring prolonged the vegetative period, and accumulated greater N, but higher late-spring and early-summer temperatures reduced the duration of grainfill period. This resulted in greater N remaining in stem and glumes due to inefficient remobilization and translocation to grain. Results suggest that nitrification inhibitors can increase aerial N accumulation, but seasonal weather patterns will ultimately determine the amount and distribution of dry matter and N into plant parts including grain.

Technical Abstract: The objectives were to determine effects of urea placement, with and without the two nitrification inhibitors (NI) Nitrapyrin [2-chloro-6 trichloromethyl) pyridine](NP) and Dicyandiamide (DCD), on aerial dry matter and N accumulation. A 4-yr field study was conducted on Renfrow fine-silty, mixed, thermic Udertic Paleustolls) silt loam near El Reno, OK. .The seven treatments included urea fertilizer (60 kg N ha-1) with and without inhibitor, surface broadcast or placed 3 to 4 cm below the seed row, and a non-fertilized control. Neither inhibitor significantly affected total dry matter accumulation, but there was a significant fertilizer response compared to control. At spike emergence in 1991, when climatic conditions were favorable for early season wheat growth, aerial dry matter and N content were greater with either NP treatment, but at harvest, both DCD treatments were greater than urea broadcast. In 1993, when climatic conditions were favorable for leaching, DCD was most effective in slowing nitrification and increasing N uptake, regardless of placement. However, despite the prolonged vegetative growth period and greater N accumulation, higher late spring and early summer temperatures reduced the duration of grainfill period and therefore yield. This resulted in greater dry matter and N content in stems and chaff, presumably because of inefficient remobilization and translocation of soluble N from vegetative parts to grain. Results suggest that NIs can increase aerial N accumulation, but seasonal weather patterns will ultimately determine the amount and distribution of both dry matter and N in wheat.