Autumn and early preplant N applications, sources, and placement may affect winter annual weed growth. Field research evaluated (1) the effect of different nitrogen sources in autumn and early preplant on total winter annual weed growth (2006–2010), and (2) strip-till and broadcast no-till N applied in autumn and early preplant on henbit (
Winter annual weeds commonly grow in no-till corn and soybean production fields [
Farmers commonly apply N to claypan soils in autumn or prior to planting due to time constraints and to allow timely corn planting. Yield differences among N sources for no-till corn [
Although research has evaluated interactions between cover crops and N availability [
Field research occurred from 2006 to 2010 at the University of Missouri Lee Greenley Jr. Memorial Research Center near Novelty, Missouri (40°01′N, 92°11′W) on a Putnam silt loam (fine, smectitic, mesic Aeric Vertic Epiaqualfs). The experiment was arranged as a factorial randomized complete block design with four replications in experimental plots measuring 3 by 15 m. The first factor was N application timing (autumn and early preplant, Table
Soil test values, nitrogen fertilizer application dates, and weed harvest dates prior to a burndown herbicide application for objectives 1 and 2.
Year | Organic | Cation | pH | Bray 1 P | Exchangeable (1 M NH4AOc) | N fertilizer dates | Winter annual | |||
---|---|---|---|---|---|---|---|---|---|---|
Matter | Exchange capacity | (0.01 M CaCl2) | K | Ca | Mg | Autumn | Early preplant | Weed harvest | ||
g kg−1 |
|
kg ha−1 | ||||||||
Objective 1 | ||||||||||
2006 | 29 | 14.7 | 6.1 | 80 | 350 | 4703 | 477 | 4 Nov. 2005 | 5 Apr. | 24 Apr. |
2007 | 26 | 13.4 | 6.4 | 34 | 305 | 5001 | 379 | 7 Nov. 2006 | 16 Mar. | 8 May |
2008 | 20 | 14.1 | 6.3 | 40 | 270 | 5017 | 442 | 11 Oct. 2007 | 7 Apr. | 6 May |
2009 | 26 | 17.3 | 6.5 | 52 | 315 | 6161 | 583 | 3 Nov. 2008 | 4 Apr. | 28 Apr. |
2010 | 28 | 15.4 | 6.8 | 31 | 233 | 6112 | 408 | 6 Nov. 2009 | 1 Apr. | 5 May |
Objective 2 | ||||||||||
2008 | 24 | 14.0 | 6.2 | 52 | 297 | 4760 | 428 | 20 Nov. 2007 | 7 Apr. | 24 Apr. |
2009 | 30 | 18.1 | 6.6 | 44 | 293 | 6648 | 519 | 3 Nov. 2008 | 4 Apr. | 4 May |
2010 | 28 | 13.9 | 6.8 | 77 | 326 | 5454 | 367 | 6 Nov. 2009 | 1 Apr. | 16 Apr. |
Mean monthly air temperature and total monthly precipitation at Novelty from 2006 to 2010, and 10-year average (2001 to 2010).
Month | Air temperature | Precipitation | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
2005-2006 | 2006-2007 | 2007-2008 | 2008-2009 | 2009-2010 | 10-yr average | 2005-2006 | 2006-2007 | 2007-2008 | 2008-2009 | 2009-2010 | 10-yr average | |
°C | mm | |||||||||||
Oct. | 12.6 | 10.4 | 14.4 | 12.1 | 9.2 | 12.0 | 85 | 60 | 86 | 77 | 225 | 98 |
Nov. | 6.6 | 6.5 | 5.3 | 4.6 | 8.4 | 6.0 | 34 | 54 | 20 | 39 | 65 | 44 |
Dec. | −2.8 | 1.8 | −2.4 | −3.6 | −2.6 | −1.5 | 23 | 64 | 48 | 59 | 44 | 41 |
Jan. | 2.7 | −2.2 | −3.3 | −5.0 | −6.8 | −2.9 | 54 | 21 | 20 | 0 | 43 | 30 |
Feb. | −1.1 | −4.8 | −4.0 | 0.3 | −5.5 | −1.8 | 2 | 68 | 99 | 42 | 23 | 49 |
Mar. | 5.6 | 9.2 | 4.0 | 6.1 | 5.9 | 5.2 | 72 | 124 | 78 | 132 | 53 | 68 |
Apr. | 14.5 | 10.0 | 10.0 | 10.6 | 14.9 | 12.5 | 62 | 106 | 116 | 121 | 146 | 109 |
May | 17.0 | 19.2 | 15.5 | 16.9 | 16.8 | 17.0 | 65 | 141 | 112 | 170 | 160 | 141 |
This experiment was arranged as a factorial randomized complete block design with three replications in experimental plots that were 3 by 23 m. The first factor was N application timing (autumn and early preplant, Table
An analysis of variance was conducted using PROC GLM [
The total density of winter annual weeds differed depending on the year and environmental conditions (Table
Winter annual weed number in the spring following N application timings. Data were averaged over N sources.
N application timing | 2006 | 2007 | 2008 | 2009 | 2010 | Average |
---|---|---|---|---|---|---|
Weed number m−2 | ||||||
Autumn | 160 | 13 | 63 | 123 | 212 | 113 |
Early preplant | 242 | 12 | 88 | 156 | 167 | 133 |
LSD ( |
35 | NS | NS | NS | NS | 14 |
Winter annual weed number in the spring following N application timings. Data were averaged over application timings.
Nitrogen sources | 2006 | 2007 | 2008 | 2009 | 2010 | Average |
---|---|---|---|---|---|---|
Weed number m−2 | ||||||
32% urea ammonium nitrate | 153 | 7 | 28 | 161 | 208 | 106 |
Ammonium nitrate | 284 | 28 | 60 | 184 | 182 | 147 |
Anhydrous ammonia | 123 | 1 | 95 | 89 | 171 | 95 |
Polymer-coated urea | 204 | 14 | 74 | 142 | 201 | 125 |
Nontreated control | 212 | 28 | 101 | 52 | 215 | 123 |
Urea + NBPT (N-(n-butyl) thiophosphoric triamide) | 215 | 3 | 79 | 222 | 183 | 137 |
Urea | 218 | 6 | 93 | 130 | 165 | 122 |
LSD ( |
77 | 15 | 46 | NS | NS | 26 |
The N sources affected total winter annual weed density, which differed by year (Table
Nitrogen application sources and timings affected winter annual weed biomass (Figure
Total winter annual weed biomass as affected by N application sources and application timings. LSD (
Winter annual weeds were smaller in autumn, while winter stress probably reduced overall biomass production compared to an early preplant application in spring. Ammonium nitrate and urea plus NBPT had greater winter annual weed biomasses compared to the nontreated control for both application timings, which was probably due to the readily available N with these N sources (Figure
This site had a uniform stand of henbit (120 to 340 plants m−2) that varied in density depending on the year. There was a significant interaction between years and N source/placement (
Total winter annual weed biomass was 28% greater (
Broadcasted urea or polymer-coated urea had greater winter annual biomass compared to a strip-till placement (Table
Henbit biomass prior to a burndown herbicide application as affected by nitrogen fertilizer source and fertilizer placement in 2008, 2009, and 2010. Data were averaged over N application timings.
Nitrogen source | 2008 | 2009 | 2010 | Average |
---|---|---|---|---|
g m−2 | ||||
Anhydrous ammonia | 143 | 39 | 66 | 82 |
Anhydrous ammonia + nitrapyrin at 560 g ai ha−1 | 114 | 15 | 35 | 55 |
Polymer-coated urea broadcast | 275 | 24 | 33 | 109 |
Polymer-coated urea strip-till placement | 83 | 13 | 25 | 40 |
Nontreated | 117 | 4 | 31 | 51 |
Nontreated strip-tillage only | 107 | 18 | 21 | 49 |
Noncoated urea broadcast | 233 | 47 | 14 | 98 |
Noncoated urea strip-till placement | 87 | 28 | 13 | 42 |
LSD ( |
108 | NS | NS | 38 |
Henbit response to an early preplant strip-tillage (7 April 2008) treatment on 24 April 2008.
A combination of tillage that decreased growth along with placement of N away from the winter annual weeds reduced henbit biomass 57 to 63% when noncoated and polymer-coated urea were strip-till applied compared to a broadcast surface N application of these N sources (Table
It was hypothesized that henbit growth would show a difference between broadcast PCU and noncoated urea due to PCU’s slow-release properties [
Greater total winter annual weed biomass resulted from an autumn or early preplant N application of certain N sources used for no-till corn production; this was probably due to the placement, availability of N, and/or injury from the N source. Total winter annual weed density was also affected by N source, but it was inconsistent over the years evaluated here. Nitrogen source selection and application timing affects the impact of N on winter annual weeds and should be considered when recommending a burndown herbicide application timing. An autumn herbicide application should be considered when autumn N fertilizer is applied to the soil surface in a no-till corn production system.
Henbit biomass was 28% greater when applying N in autumn compared to an early preplant application timing. Nitrogen placement with strip-till placement helped reduce henbit biomass prior to a burndown herbicide application compared to a broadcast N application. Using strip-tillage N placement may also reduce interference associated with winter annual weeds, which may allow a delayed postemergence burndown application compared to a broadcast surface N application.
N-(n-butyl) thiophosphoric triamide.
Buttercup species
Carolina foxtail
Corn
Field pennycress
Henbit
Horseweed
Purslane speedwell
Shepard’s purse
Small flower bittercress.
The author declares that there is no conflict of interests regarding the publication of this paper.
The author would like to thank Patrick Nash, Randall Smoot, Chris Dudenhoeffer, and Clinton Meinhardt for their technical assistance with this research. A special thanks is extended to the Missouri Fertilizer and Ag Lime Board for their financial support.