CROP ROTATION AND RESIDUE DURABILITY
EFFECTS OF SPRING CROPS ON WINTER
WHEAT IN THE PALOUSE REGION
Stephen O. Guy, Department of Plant, Soil and Entomological Sciences,
University of Idaho, Moscow, Idaho 83844-2339, USA
Contact: Stephen Guy (ph. 208-885-6744)
Email: sguy@uidaho.edu
Introduction
The Palouse is a 1.3 million hectare dryland farming area in northern Idaho and
eastern Washington, USA. Here winter wheat (T. aestivum L.) usually follows
grain legumes such as dry pea (Pisum sativum L.) and lentil (Lens culinaris
Medik.). Steep sloping loessial soils and frequent freeze-thaw cycles result in high
soil losses. During the critical November to April erosion period, a minimum of 30
to 50% surface residue cover is needed to control erosion to an acceptable level .
Winter wheat in northern Idaho has shown significantly higher yields following dry
pea than following spring canola (Brassica napus L.), mustard (Sinapis alba L.), or
barley (H. vulgare L.) during years of limited moisture (Guy and Gareau, 1998).
Mustard and canola crops provide greater production potential and reduced disease
levels in subsequent winter wheat crops when compared to wheat or barley
preceding winter wheat (Angus et al., 1991. Nitrogen (N) response in winter wheat
can vary due to previous crop because of differences in N fixation, residual
inorganic N, soil moisture, soil physical changes, pest dynamics and crop residue
interactions (Angus et al., 1991; Guy and Gareau., 1998; López-Bellido et al.,
1996).
The objective of these experiments is to evaluate rotational effects of crops grown
previous to winter wheat for previous crop performance, residue production and
persistence, and relative winter wheat performance from the previous crop effects.
Materials and Methods
Condiment mustard, dry pea, and lentil were planted in April of 1994 and 1995 in
a randomized complete block design with four replications in a Palouse silt loam
soil near Moscow, Idaho, USA. Individual plots were 7.6 m by 152 m in 1994 and
4.9 m by 183 m in 1995. The harvest combine was equipped with a chaff spreader
to distribute residue onto each plot area. Crop residues were collected from three
areas in each plot inside a template area of 0.75 m2 placed across the crop rows.
Residual inorganic N was determined to 0.9 m soil depth before winter wheat
planting. Seedbed preparation for the subsequent winter wheat crops (Crop Year 2
of each 2-year cycle) was done using conventional tillage and seeding operations.
A line-point method was applied to determine percent residue surface cover along
a 15 m tape-line. Monthly residue evaluations were taken when conditions allowed
from October through April. A 15 m end section in each plot area was divided into
sub-plots to establish N fertilizer trials at rates of 0, 45, 90, 135, 180, and 225 kg N
ha-1 using the previous spring crop as the main plots, and N rates as sub-plots. The
remaining large plot areas were top-dressed with 80 kg ha-1 of N fertilizer. All
areas received 49 kg N ha-2, 27 kg P2O5 ha-2, and 18 kg SO4 ha-2 incorporated prior
to winter wheat seeding.
In small plot rotation trials (9.1 m by 7.6 m), winter wheat, spring wheat, spring
barley, spring canola, mustard, crambe (Crambe abssinica Hochst.), winter rape (B.
napus L.), and dry pea were grown from 1991 to 1995 prior to a winter wheat crop.
Winter wheat was uniformly cropped across the previous crop areas before
dividing into sub-plots for variable N fertilizer application evaluation. The previous
crop influences were assessed for the following winter wheat crop agronomic
performance and N fertilizer response. Yield responses across years for previous
crop effects on winter wheat were compared as a percent of the yield of wheat
yield following pea.
Results and Discussion
Spring crop performance and residue evaluation
Seed yields were different among the three spring crops in the large plot trials
(Table 1). The pea and lentil seed yields were above average for the region.
Mustard seed yields were slightly lower than expected due to lack of moisture from
May through July in 1994 and due to establishment and weed problems in 1995.
Soil N nitrate and ammonia assessed to 0.9 m soil depth after harvest was not
different among the spring crops.
Table 1. Seed yield, residue production and after-seeding residue surface cover
persistence of three spring crops grown during 1994 and 1995 and winter wheat
yield following the spring crops near Moscow, Idaho, USA
Crop Yield
Overwinter Residue
Residual
Winter
Spring Crop Seed Residue Soil N Oct Dec Feb Mar Wheat Yield
kg ha-1
% Surface Cover
kg ha-1
Mustard
1230 6300
48
58
59
62
61
7100
Pea
3460 3470
49
33
31
30
28
7500
Lentil
2420 4170
39
28
28
26
26
7600
Average
2370 4650
46
40
38
36
35
7400
ns
10
6
7
3
ns
LSD (0.05) 480
920
Despite the lower seed yield, the residue produced by mustard was significantly
higher than pea or lentil (Table 1). Total biomass (seed + residue) averaged 7530
kg ha-1 for mustard, 6930 kg ha-1 for pea and 6590 kg ha-1 for lentil. This benefit of
high residue production and potential erosion reduction contributes to the value of
mustard as a crop and is an advantage over dry pea or lentil. Harvest index
(seed/(seed + residue) x 100), was significantly different among the three spring
crops, 50% for pea, 37% for lentil, and 16% for mustard.
Residue surface cover was 100% for mustard, 88% for lentil, and 84% for pea after
harvest. Residue surface cover was reduced during seedbed preparation and
planting of winter wheat to 58% for mustard, 33% for pea, and 28% for lentil
(Table 1). Residues from all three crops were more durable over the winter than
expected, showing little change in surface cover until March. The seedbed
preparations and planting of the winter wheat in 1994 were done in dry conditions
and little rain fell until late October, slowing the residue decomposition rate. When
residue surface cover started to decrease, winter wheat and weed growth after
March more than compensated for the decline in crop residue. Residue cover
measured on the mustard plots was consistently above the 30 to 50% target level
set by USDA conservation plans for erosion control. Pea residue over-winter
surface cover was just below this target level after December, while lentil residue
was below the target level at all times after seedbed preparation and planting of the
winter wheat. This shows the difficulty in providing adequate surface groundcover
following legume crops. Also, lentil residue is incorporated or lost from the surface
to a greater extent than pea residue from tillage used in these experiments. This
probably is due to the smaller size and greater fragility of the lentil residue.
Effect of previous crop on winter wheat performance
In the 1994-95 trial, winter wheat yields were significantly higher following pea
and lentil than following mustard. In the 1995-96 trial, however, wheat yield was
not significantly different among previous crop treatments. Averaged over both
trials, wheat yields were not different among previous crop treatments (Table 1).
Winter wheat grain test weight differences were small, but were highest when
wheat followed lentil. There were no significant differences due to previous crop
for winter wheat grain protein content or seed weight.
Winter wheat seed yield increased 60% as spring applied N rate increased from 0
to 180 kg ha-1. As shown by regression analysis, yield response to fertilizer N was
not different among previous crops in regression line slope or position (R2 = 0.98
to 0.99). However, Linear plateau regression analysis of winter wheat yield
response to fertilizer N (R2 = 0.97 to 0.99) revealed optimum fertilizer rates of 135
kg ha-1 following pea or lentil, and 180 kg ha-1 following mustard. This plateau was
at a wheat yield of 9400 kg ha-1 following pea and mustard, and 9200 kg ha-1
following lentil.
Winter wheat yield following eight crops
Results pooled from five crop sequence trials show that winter wheat yield
following pea and spring Brassica crops were highest (Figure 1). These trials did
not include results from 1994 trials when a dry growing season allowed wheat
yield response to residual soil moisture after pea that gave a 20 to 30% yield
advantage for winter wheat following pea. Results from other years do not show
this advantage to pea over mustard, canola, and crambe as previous crops to wheat.
Winter rape did not appear to be as beneficial of a previous crop as spring canola,
mustard, or crambe. Wheat yields were at least 25% less following wheat than after
canola, mustard, crambe, or pea. These crop sequence trials show that the more
different a crop is previous to winter wheat, e.g. spring broadleaf, the greater the
rotation advantage. Rotation of broadleaf crops with grass crops appears to be
more important than rotating spring and fall crops when weed control is not a
factor. In some experiments it appears there was also a rotational advantage to
previous crops that do not use all the soil moisture when the following crop season
available moisture is limiting to wheat production.
Figure 1. Winter Wheat Yields Following Previous Crops as a Percent of Yield
following Pea from Four Experiments near Moscow, Idaho, USA
Conclusions
Mustard, canola, crambe, pea and lentil are excellent rotation crops prior to winter
wheat. Additionally, some years pea and lentil can provide some carryover soil
moisture for dry growing conditions and fix nitrogen. Brassica crops such as
mustard, canola, and crambe are excellent rotation crops and provide large amounts
of crop residue that is important for erosion control. Grain legumes must be better
managed for residue production and retention for soil erosion control. These
broadleaf crops are important for sustainable crop production systems on the
Palouse and will continue to be grown in rotation with winter wheat.
References
Angus, J., Van Herwaarden A., and Howe G. 1991. Productivity
and break crop effects of winter growing oilseeds. Australian
Journal Experimental Agriculture 31:669-677
Guy S. and R. Gareau. 1998. Crop rotation, residue durability, and
nitrogen fertilizer effects on winter wheat production. Journal of
Production Agriculture 11:457-461
López-Bellido L., Fuentes M., Castillo J., López-Garrido F. and
Fernández E. 1996. Long-term tillage, crop rotation, and nitrogen
fertilizer effects on wheat yield under rainfed Mediterranean
conditions. Agronomy Journal 88:783-791