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A Quarter Century of a Tillage-Rotation-Nitrogen Rate Study in Nebraska
ABSTRACT
A long term tillage, nitrogen rate and rotation study was analyzed using standardized precipitation indexes to determine if sub setting the data by precipitation/ET could establish specific relationships between the main effects. The study, initiated in 1986 on a silt loam, under rain-fed conditions in the western corn belt generally showed that under dry conditions No-till increased yields, and under wet conditions No-till was of no benefit. Nitrogen effects were less pronounced under dry conditions, and there were 5 years of 18 normal years where N rates applied were not sufficient to maximize yield.
BACKGROUND
OBJECTIVES
Determine the interaction between Tillage, Rotation and N. rate for corn production under different moisture conditions.
Compare standard precipitation indexes and determine their usefulness.
EXPERIMENTAL SETUP
RESULTS
RESULTS
CONCLUSIONS
For 6 Dry Years:
• N response was minimal
• Year x Tillage x Rotation was significant since in severe drought corn following soybeans were not increased:
• Moderate drought increase from C-S, 21%
• Severe drought increase from C-C, 17%
Normal years:
• C-S consistent, 28% increase
• Year x N rate effect was significant:
Linear response (5 years) and quadratic (12 years) .
Wet years:
• Tillage was significant.
• Plow 4.1% and Disk 0.7% > yield than No-till.
SPEI is a better tool than SPI for moisture prediction.
Charles A. Shapiro1 and Ankit Shekhar2 1 Haskell Agricultural Laboratory, University of Nebraska- Lincoln 2Former summer intern
Traditional ANOVA of this experiment indicated that there were significant year x treatment interactions. In an effort to generalize how corn was responding to the tillage, N rate, and rotation treatments, we attempted to separate the years out by the precipitation/ET history for each year.
Tillage Systems: Crop Rotation (summer): N rates(Ammonium Nitrate):
Moldboard plow Continuous Corn (C-C) 0 kg ha-1
Disk Tillage Corn Soybean (C-S) 40 kg ha-1
No-till 80 kg ha-1
120 kg ha-1
160 kg ha-1
METHODS
SPEI & SPI
SPEI (Standardized precipitation evapotranspiration index) was calculated according to Vicente-Serrano et al., 2010.
𝐷𝑖 = 𝑃 − 𝐸𝑇
SPI(Standardized precipitation index was calculated according to McKneeet al.,1993
SPEI and SPI for five, 12 and seven months was considered for the analysis.
Climatic Variability
Average yearly rainfall (1973-2014) – 702 ± 187 mm
5 wet years – 1993 and 2014 were extremely wet.
6 dry years – 2012 and 1988 were extremely dry.
18 normal years.
-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011 2013 2015SPEI
Year
SPEI values for the study period
SPEI-5 SPEI-12
Wet
Normal
Dry
Table. Effect of tillage and rotation over years and by
wet, normal, and dry years using the SPEI.
Tillage Rotation 29 year average Wet Normal Dry
------------------------- Mg ha-1 ------------------------
Plow CC 6.6 8.2 6.9 4.2
Corn-soy 8.1 9.4 9.1 4.1
Disk CC 6.8 8.1 7.1 4.7
Corn-soy 8.2 9.5 9.1 4.6
No-till CC 6.8 7.7 7.2 4.8
Corn-soy 8.4 9.3 9.1 5.5
ANOVA
Tillage x Rotation NS * * ***
Average rainfall(mm) 730 1016 747 511
0.00
2.00
4.00
6.00
8.00
10.00
12.00
-2.500 -2.000 -1.500 -1.000 -0.500 0.000 0.500 1.000 1.500 2.000 2.500
Co
rn Y
ield
(M
g h
a-1
)
SPEI -12
Tillage vs SPEI
Disk
No-till
Plow
R² = 0.4916
R² = 0.4472
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
-2.500 -2.000 -1.500 -1.000 -0.500 0.000 0.500 1.000 1.500 2.000 2.500
Yie
ld D
iffe
ren
ce
SPEI-5
Fertilization and rotation effects over SPEI range
Unf Fer
YDUC = (C-S)max, unfertilized – (C-C)max, unfertilized YDFC = (C-S)max, fertilized – (C-C)max, fertilized