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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