16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11798
Season-long supply of plant-available nutrients from compost
and fertiliser in a long term organic vs. conventional snap bean
rotations experiment
Owen, J.1, LeBlanc, S2 & Fillmore, S.A.E.3
Key words: compost, plant nutrients, ion exchange membranes, seasonal changes
Abstract
In Canada, stockless organic vegetable cropping systems may use compost for
fertility. However, information to guide growers about when nutrients become available
in the soil over the growing season is lacking. Detailed analysis of plant nutrient supply
was conducted over three years in a multi-site rotations experiment using two
cropping sequences. The experiment compared conventional fertility treatment
(synthetic fertiliser (1x N)) with organic treatments (annual compost amendment at a
low (1x N) and a high rate (3x N)). Plant-available soil nutrients were captured using
sequential two-week burials of ion exchange membranes. Ions were eluted and
quantified. Variation in nutrient supply over time, and effects attributable to crop
rotation and fertility regime were evaluated with analysis of variance and of principal
components. Results showed season-long supply of plant nutrients was more affected
by year than fertility regime or rotation, even in composted plots where large residual
effects were expected. Synthetic fertiliser and 1x compost resulted in very similar
seasonal plant nutrient supplies. While 3x compost caused some significant changes,
the gains in plant nutrient supply was modest enough to suggest little or no advantage
in this one respect to warrant the cost of amending at greater than the 1x rate.
Introduction
Plant nutrient supplies available for crop growth in organic systems are often
comparable and sometimes exceed those found in conventional systems, yet
synchronizing the availability of those nutrients may be more difficult (Berry et al.,
2002). Because composition of compost is notoriously variable, and mineralization of
organic matter in the soil is mediated by a host of factors such as temperature,
moisture, soil chemistry and microbial communities (Magdoff and Weil, 2004),
predicting the timing and quantity of nutrient supply in the soil becomes difficult. While
beneficial effects of compost are well documented (Rosen and Allen, 2007) growers in
Canada still often rely on rules of thumb about nutrient availability in the first year to
determine application rates. This study used ion exchange membranes to evaluate
season-long plant nutrient availabilities in soils amended with two rates of compost,
compared with soils amended with synthetic fertilisers, over three years in a
continuous bean cropping system, and a fully phased snap bean/fall rye rotation.
1
Senator Hervé J. Michaud Research Farm, Agriculture and Agri-Food Canada, 1045 St. Joseph
Road, Bouctouche, New Brunswick, Canada E4S 2J2, E-Mail: OwenJ@agr.gc.ca Internet
www4.agr.gc.ca/AAFC-AAC
2
3
As above
Atlantic Food and Horticulture Research Centre, Agriculture and Agri-Food Canada, 32 Main
Street, Kentville, Nova Scotia, Canada, B4N 1J5 E-mail: FillmoreS@agr.gc.ca Internet
www4.agr.gc.ca/AAFC-AAC
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11798
Materials and methods
This research was conducted over three years of a long term organic-versusconventional rotations experiment, with three replicates at a research farm site and
three at a commercial farm site in Bouctouche, New Brunswick, Canada. Each
replicate comprised three strips, to which each was assigned a rotational cropping
sequence (continuous beans (CB), fully phased beans/fall rye two-year rotation (BRB
or RBR)). Strips were divided into plots to which were assigned one of three yearlyapplied fertility treatments (synthetic fertiliser, low (1x) rate compost, high (3x) rate
compost). Compost was a commercial organic certified mix of forestry, fishery and
farmyard waste (Cardwell Farms Compost Products, Penobsquis). It had a carbon to
nitrogen ratio of 15.2, with total nitrogen on a dry matter basis of 1.5%. The 1x
compost was applied at a rate calculated to deliver the equivalent of 50 kg N ha-1: the
same rate of N applied in synthetically fertilised plots. N, P and K amendments in
synthetically fertilised plots were based on regional crop production guides. Amounts
of nutrients added in each treatment are summarised in Table 1.
Anion and cation exchange membranes were used to monitor supply of plant-available
ions in the soil solution of bean plots. The membranes, Plant Root Simulator™ probes
(Western Ag Innovations, Saskatoon), were buried vertically in the soil, each exposing
an area of 17.5 cm2 of ion-exchanging surface to the soil at approximately six to
thirteen cm below the soil surface. Four pairs of anion and cation probes were buried
on the crop row in each plot to form composite samples to account for soil
heterogeneity. Each pair of probes was shielded from interference by plant roots by a
length of pvc pipe hammered into the soil. Probes were buried for sequential two-week
periods, for 6, 7 and 8 burials in 2003, 2004 and 2005, respectively. Each new set of
probes was inserted directly into the holes left by the previous set. In the laboratory,
ions adsorbed to the membranes were eluted and quantified by colorimetric or
inductively coupled plasma techniques. Because burial dates varied from year to year
according to the cropping season, seasonal curves of nutrient supply were developed
for each year, and from these curves, predicted values were generated for a specific
set of dates. Principal components were computed for seasonal totals of plant
nutrients supplied in bean plots, and presented in biplot form.
Tab. 1: Three-year totals of plant nutrients (kg ha-1) applied as synthetic
fertiliser, low rate (1x) or high rate (3x) compost to plots in continuous beans
(CB), Beans-Rye-Beans (BRB) and Rye-Beans-Rye (RBR) crop sequences.
Treatment
Synthetic
fertiliser
Compost 1x
Compost 3x
* not analysed
Crop Seq.
CB
BRB
RBR
CB, BRB, RBR
CB, BRB, RBR
N
150
200
250
150
450
Nutrients applied (kg ha-1)
P
K
Ca
Mg
Fe
210
215
0
0
0
140
215
0
0
0
70
215
0
0
0
107
93
271
60
88
321
279
813
180
264
Al
0
0
0
*
*
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11798
Results and discussion
Extended burials of ion exchange membranes provide an opportunity to measure the
nutrient supply rate in soils over time while accounting for short term dynamic
interactions of nutrients within the root zone (Qian and Schoenau, 2002). In this study
sequential burials captured season-long plant nutrient supplies over three years.
Compost application, particularly at the 3x rate, was expected to increase the supply
of nitrogen and other plant nutrients. Supply rates tended to be similar between the
synthetic fertiliser and the 1x compost treatment (Figure 1). NO 3-N supply was
greatest in the synthetic fertiliser treatment, and decreased significantly with
increasing compost amendment, likely because the addition of massive amounts of
organic C in the compost treatments over the years immobilised N. Potassium supply
increased significantly with increasing compost, though potassium supplied at the 3x
compost rate was only about 65 kg ha-1 greater than that applied as synthetic fertiliser
(Table 1). The modest differences in nutrient supplies between 1x and 3x compost
treatments was surprising, suggesting that while organic matter increased (data not
shown) this did not translate into gains in nutrient supply proportionate to the inputs.
Biplot analysis (Figure 2) revealed clear clusters of fertility treatments by year. Nutrient
supplies were least in 2003, but despite high inputs of compost, did not increase
incrementally by year in compost amended plots. In 2004, nutrient supply exceeded
nutrient supply in 2005, suggesting that year effects play a defining role in nutrient
supply. Mg and K were affected in much the same way by fertility treatments,
independent of Fe, Al and P which formed another tight cluster. In acid soils, such as
those of this study, inorganic P precipitates as Fe/Al-P secondary minerals and may
become adsorbed to Fe/Al oxides (Tisdale et al., 1993). The association of Fe, Al and
P with the 1x and 3x compost treatments in 2004 is therefore likely related as well to
an increase in pH found in composted treatments (data not shown). Ca and N supply
were most affected by 1x compost and synthetic fertiliser treatments. Overall, the
average nutrient supply among all treatments was best represented by 1x compost in
the CB rotation in 2005, with total season supplies (mg ion cm-2 per 12 weeks) of:
NO3-N, 2287; NH4-N, 41; P, 70; K, 2063, Ca, 8397; Mg, 1613; Al, 224; and Fe, 259 mg
ion cm-2. Other factors likely contributed to the year effects, including crop uptake, and
crop residues returned to the soil, which would have differed by crop, and possibly by
treatment as well. These important relationships will be explored at length elsewhere.
Ion capture (mg ion*cm-2*2 weeks)
8000
synthetic fertiliser
Ca
1x compost
Ca
3x compost
Ca
6000
4000
NO3-N
2000
0
June 15
July 1
July 15
August 1 August 15
Date
K
Mg
NO3-N
K
Mg
P
P
Sept 1
June 15
July 1
July 15
August 1 August 15
Date
Sept 1
K
NO3-N
Mg
P
June 15
July 1
July 15
August 1 August 15
Sept 1
Date
Figure 1: Cummulative supply of plant nutrients in soils amended with synthetic
fertiliser, 1x compost and 3x compost, over three years and two cropping
sequences.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11798
6
4
h5
h4
H3
NO 3 -N
NH 4-N
h3
2
H5
l5
0
L5
H4
l4
Score 2
L4
-2
F4
f4
F3
F5
Ca
Mg
K
P
Fe
Al
L3
l3
f3
f5
-4
-6
-6
-4
-2
0
2
4
6
Score 1
Figure 2: Biplot of principal components of fertiliser amendment/crop sequence
on seasonal total plant nutrient supplies (caps refer to Continuous Beans; lower
case to Beans/Rye; 3, 4, 5 to 2003 to 2005; letters l, h, f to low (1x) and high rate
(3x) compost and synthetic fertiliser)
Conclusions
Compared with synthetic fertiliser, compost application resulted in less NO 3-N, and
greater amounts of K and Ca over the course of the season. Nutrient supply was more
affected by year than by any other factor, with the effect of year resulting in lower
nutrient supplies in 2004 than in 2005 despite any residual contributions of previous
years’ compost applications. Applying 3x compost increased Ca and K supplies, but
other gains were not enough to warrant the considerable associated costs.
Acknowledgments
This work was supported by AAFC’s Matching Investment Initiative, Cardwell Farms
Compost Products, Western Ag Innovations, La Ferme Michaud and Beatrice Allain.
References
Berry, P.M., Sylvester-Bradley, R., Philipps, L., Hatch, D.J., Cuttle, S.P., Ryans, F.W. and Gosling,
P. (2002) Is the productivity of organic farms restricted by the supply of available nitrogen?
Soil Use Mgt 18: 248-255.
Magdoff, F. and Weil, R,R. [eds.] (2004): Soil Organic Matter in Sustainable Agriculture. CRC
Press, Boca Raton. p. 398.
Rosen, C.J. and Allan, D.L. (2007) Exploring the benefits of organic nutrient sources for crop
production and soil quality. HortTechnology 17: 422-430.
Tisdale, S.L., Nelson, W.L., Beaton, J.D. and Havlin, J.L. (2004) Soil Fertility and Fertilizers (5th
Ed.)Macmillan Publishing Co., New York. p. 634.
Qian, P. and Schoenau, J.J. (2002) Practical applications of ion exchange resins in agricultural
and environmental soil research. Can. J. Soil Sci. 82: 9-21.