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Renovation of established forages with fertilizer

Using fertilizers to restore the productivity of established forage crop stands pays major dividends.


November 20, 2007
By Stewart Brandt Guy Lafond Bill May and Adrian Johnston

Topics

Forage crop fertilization is considered an optional practice for many farmers
in the northern Great Plains, especially where dryland conditions limit the
forage yields. However, there is a large database to support fertilization of
forages as a means of maintaining yield, quality and stand purity. In fact,
the cost of not fertilizing is much higher when stand productivity declines.
This project was established to evaluate dry and fluid fertilizer use on old,
established stands of grass-legume forages.

Forage crop stands were selected at Scott (Typic Boroll loam soil) and Indian
Head (Udic Boroll clay loam soil), Saskatchewan. At Scott, the stand was a mixture
of crested wheatgrass, bromegrass and alfalfa (10 percent). At Indian Head,
it was bromegrass and alfalfa (30 percent). At Scott, the stand was extensively
invaded by fescue and bluegrass species, which are considered less productive
when harvested as hay. Both stands were old and nutrient deficient. However,
both were weed-free.

Soil tests were taken at the start of the project: N and sulphur (S), zero
to 24 inches deep; P (modified Kelowna); and potassium (K), zero to six inch.
Results showed 21 pounds N/ac, six pounds P/ac, >600 pounds K/ac, and 60 pounds
S/ac at Scott, and 25 pounds N/ac, two pounds P/ac, >571 pounds K/ac, and 72
pounds S/ac at Indian Head.

Fertilizer treatments were applied to the study area in plots six feet by 25
feet. The treatments were:

  1. unfertilized check,
  2. unfertilized check with coulter (12 inch centres) applied in year one and
    coulter applied urea ammonium nitrate (UAN) and ammonium polyphosphate (APP)
    in years two and three,
  3. surface broadcast ammonium nitrate (AN) and mono-ammonium phosphate (MAP),
  4. dribble banded (12 inch centres) UAN and APP,
  5. dribble banded UAN and APP with ammonium thiosulphate (ATS) added at one
    percent of total solution,
  6. coulter injected (12 inch centres) UAN and APP,
  7. coulter injected UAN, and
  8. coulter injected UAN and APP at three times the annual rate (see Table 1).

Rates of N used at Scott were 53 pounds N/ac in 2002 and 2004, and 27 pounds
N/ac in 2003. At Indian Head, the rate was 75 pounds N/ac each year. With the
exception of Treatment 8, all plots received 30 pounds P2O5/ac
each year with the N. Treatment 8 received 90 pounds P2O5/ac
in year one and then only N each year after. Treatments were applied annually
to the same plot area and forage yields were harvested once each year.

Yield response after the first fertilizer application (year one) was consistent
over location years, but in the second and third years of application, there
was a significant location by treatment interaction. Most, if not all, the interaction
effect could be attributed to a difference in responses to P alone at the two
locations. At Scott, a small response to N without P was recorded after years
two and three, while at Indian Head the N alone treatment yielded the same as
the no fertilizer treatment (data not shown).

Table 1. Average yield response to
fertilizer N and P additions on established legume-grass forage stands at
Scott and Indian Head, Saskatchewan.
  Forage yield, lb/ac
Treatment Year one Year two Year three Mean
1. Check with no fertilizer. 1193 1210 997 1130
2. Coulter check with no fertilizer year one, coulter applied UAN1
and APP in year two and three.
1059 1682 2456 1736
3. Broadcast AN and MAP. 1771 2723 3088 2528
4. Dribble UAN and APP. 1825 2706 2537 2359
5. Dribble UAN with 10 percent ATS + APP. 1914 2581 3035 2510
6. Coulter UAN and APP. 1566 2456 2830 2287
7. Coulter UAN. 1406 1673 1362 1477
8. Coulter UAN and three times APP2 1914 2786 3008 2572
LSD p=0.05 325 291 354 
1 UAN = urea-ammonium nitrate; APP
= ammonium polyphosphate; ATS = ammonium thiosulphate; AN = ammonium nitrate;
MAP = mono-ammonium phosphate.
N rate was 53lb N/ac in 2002 and
2004, 27lb N/ac in 2003 at Scott; 75lb N/ac in all years at Indian Head.
Annual P rate 30lb P2O5/ac.
2 Three times APP with ammonium polyphosphate
applied at three times the annual rate (90lb P2O5/ac)
in year one only, with N applied each year.

Dribble banding liquid UAN and APP was an effective means of applying fertilizers
to old, established forage stands (see Table 1). The yield was similar for surface
broadcasting granular AN and MAP and the fluid UAN and APP. Adding ATS to liquid
UAN appeared to provide a slight (not statistically significant) benefit over
UAN alone. If this treatment adds little to fertilizer cost, it may be useful
as insurance against N losses under adverse conditions. No advantage was recorded
to coulter application of the fluid fertilizer bands in this study (see Table
1). Dribble band application is a lower cost method than use of coulters and
this research would not support the investment, upkeep and operational cost
of using coulters on forage lands.

Applying a three year supply of P at the beginning of the project was as effective
as applying equal increments of P annually. In fact, at Indian Head, the application
of the three year P rate in year one was always the highest yielding treatment
(data not shown). Only when N and P were applied together was there a yield
response at Indian Head, indicating that P was the major limiting nutrient.
Applying P only at Scott did increase yield, but was ineffective compared to
N plus P treatment (P alone yielded 1566lb/ac compared to no fertilizer at 1344,
and broadcast N and P at 2314lb/ac).

The residual effect of repeat fertilizer applications to these plots was dramatic.
Check yields remained somewhat static, but fertilized yields tended to increase
over time, typically increasing by about 50 percent in the first year of application.
In the second year of application, the most effective fertilizer treatments
more than doubled yields. In the third year, yields were tripled. These responses
support previous research in the region, which showed a progressive improvement
in forage response to P additions over a series of years. Where banding without
fertilizer was done the first year (Treatment 2), followed by fertilizing in
each of years two and three, yields continued to be lower than where fertilizer
N and P were coulter-banded all three years.

Where the productivity of established forages has declined over time due to
nutrient deficiencies, fertilizer additions can be an effective means of improving
yields. Soil testing to evaluate the level of available nutrients is critical
to ensure that all deficient nutrients are applied. Correcting deficiencies
in P can be critical to achieving a profitable N response in forage crops. -30-

*Mr. Brandt is an agronomist with
Agriculture and Agri-Food Canada in Scott, Saskatchewan; Dr. Lafond and Mr.
May are agronomists with Agriculture and Agri-Food Canada in Indian Head, Saskatchewan;
Dr. Johnston is PPI/PPIC Northern Great Plains Director, Saskatoon, Saskatchewan.
Reprinted from Better Crops with Plant Foods, with permission of PPI/PPIC.