Beneficial use of Paper-Mill Residue Compost in Potato Production
R.R. Simard1. R. Lalande1, B. Gagnon1. G. Parent and P. Parent2
1Soils and Crops Research Centre.
Agriculture and Agri-Food Canada.
Sainte-Foy, Qc.
2Horticultural Research Centre.
Laval University, Qc
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Abstract
Paper sludge compost may be an efficient way to improve the nutrient status and biochemical and physical properties of coarse-textured soils devoted to intensive potato production. A study was initiated to assess the impact of addition of a compost of primary papermill sludge and hog manure, used alone or in combination with inorganic fertilizers, on soil quality and potato (Solanurn Tuberosum L. Hilite Russet) yields on a Bevin sandy loam (Orthic Humo-Ferric Podzol) located in St-Ubalde, Québec, Canada. The compost was applied in spring at 0,40,80 and 120 Mg ha-1 on a wet basis, and was supplemented or not with 0 to 225 kg N ha-1, 0 to 300 kg P205 ha-1 and 200 kg K20 ha-1. The compost was incorporated in the top 10 cm of soil. The inorganic fertilizers were fractionated at planting and hilling.
The addition of 40 Mg
compost ha' produced the highest marketable tuber yields independently of
the inorganic fertilizer supplement. This amount of compost along with 75
to 150 kg N or 100 to 200 kg P205ha-1produced
the highest yields. Compost reduced the degree of potato scab coverage on
the tubers. Compost addition significantly influenced the soil Kcl extractable
N 30 days after planting and Mehlich-3 extractable P and K contents at potato
harvest. Enzyme activities were maxima early in the season. Compost addition
at 40 Mg ha-1 resulted in the highest enzymatic activity, Nitrobacter
sp. counts and C-CO2 evolution. Compost addition also influenced
the synthesis of particular microbial phospholipid patterns. Addition of
inorganic fertilizers to compost resulted in higher enzyme activity than
compost alone but had little effect on C mineralization or microbial biomass
C. Addition of 120 Mg compost ha-1 was excessive. Compost, when
added at a reasonable rate (40 Mg ha-1), is a good way to increase
the inorganic fertilizer efficiency by increasing potato tuber yields and
soil quality.
Introduction
Soils used for potato production in Eastern Canada are normally of coarse texture and are subject to degradation when crop rotations are not frequently used. Loss of organic matter is the main form of degradation (Tabi et al. 1990) which results in loss of aggregate stability and increased water (Edwards 1988) or wind erosion. Loss of organic matter and erosion result in diminished water retention capacity, resistance to compaction and cation exchange capacity (Saini and Grant 1980). The N mineralization potential from soil humus will also be decreased since it is closely related to the soil organic matter content (Simard and N'dayegamiye 1993). All of this may result in yield losses and increased fertilizer and irrigation cost (Saini and Lantagne 1974).
Rotations involving crops
with large amounts of residues are certainly a good alternative in organic
matter management. Large inputs of exogenous organic materials would be
preferable if a rapid increase in organic matter content is targeted. The
pulp and paper industry generates about 1.5 million tons of residues per
year in Quebec (Association des industries forestières du Québec
1997). Although excellent results in term of improvement of soil quality
and crop yields have been obtained in crop production with the raw sludge
materials (Trépanier et al. 1996; Simard et al. 1998 a, b), these
materials have the disadvantages of generating bad odours and composting
may be the solution. Also, land spreading of the raw material is only possible
in a part of the year. Composting reduces volume and odour and stabilize
the organic C (Lampkin 1990). Using of composted materials may have a longer
impact on organic matter content than raw materials on these coarse textured
soils (Barker 1997). Composted de-inking sludge was previously shown to
result in improved soil quality, nutrient efficiencies and crops yields
in winter cabbage and dry bean production (Simard et al. 1996, 1997). The
objective of this study was to assess the impact of addition of a de-inking
paper sludge-hog manure compost on soil quality and potato tuber yields
and quality.
Materials and Methods
Experimental design
The experiment is carried out in a field of Les Patates Herman Dolbec in St-Ubalde, Québec, Canada. The soil is a Bevin loamy sand (Orthic Humo-Ferric Podzol). The soil had a pH of 5.4 and 45-60 g kg-1 organic matter. The compost was applied at 0,40, 80 and 120 Mg ha-1 on a wet basis. Treatments including combinations of 0 to 225 kg N as ammonium nitrate, 0 to 300 kg P ha-1 as triple superphosphate and 0 to 200 kg K ha-1 as potassium chloride were added as subplots. Treatments were arranged in a completely randomized split-block design with compost rates as main plots and fertilizer combinations as subplots. All treatments were replicated three times. Compost and inorganic fertilizers were hand-applied on May 28 at pre-seeding and immediately incorporated with disk harrow. Two third of the N fertilizer were applied at seeding and the rest at hilling. Potatoes (cv. Hilite Russet) were planted the next day with a 35 cm in-row spacing and 91.5 cm between rows. Pesticide management was as recommended in Québec (CPVQ 1992). Plots were hand harvested on September23 and tubers were classified according to size in Canada #1 categories.
Soil chemical analysis
Samples were taken prior
to the beginning of the experiment from the 0-20, 20-40 and 40- 60 cm with
a 7 cm auger. Three cores were taken per plot. The samples were air-dried
and sieved to 2 mm prior to analysis. Samples were also taken 1 month after
planting and at harvest. The soil pH was measured in 0.01 M CaCl2(1:2
soil : solution); P, K, Ca, Mg and metals were extracted by the Mehlich-3
solution (Tran and Simard 1993). The P content in the extracts was determined
by colorimetry using the molybdate reaction (Murphy and Riley 1962) whereas
the other elements were determined by flame (K) or atomic absorption spectroscopy.
The soil inorganic N was extracted by 2 M KCl (Maynard and Kalra 1993).
The NH4+ content of the extracts was determined by
the colorimetric reaction with nitroprusside (Nkonge and Ballance 1982)
whereas the N03- was determined by liquid chromatography
on a Dionex 4000i apparatus equipped with a VDM-II UV Vis-detector (Dionex
Corporation, Sunnyvale, CA).
Characterization of biochemical properties
Sampling (0-20 cm) was
carried out on May 28, June 15, June 25, July 23, August 20, September 17
and October 14. The samples were composed of at least 19 cores taken from
the side of the potato hill. Soils were sieved to 4 mm in the field and
carried in a refrigerated chest to the laboratory where they were stored
at 40C. All analysis were carried out within three weeks of sampling.
Carbon mineralization was carried out according to Zibuske (1994). Briefly,
25 g of fresh soil were added to 0.5 L glass Massontm jar with
a NaOH trap. Pots were closed and incubated at 250C in the dark
for up to 42 days. Evolved C02was measured, after precipitation
with excess of BaCl2, by titration of the residual NaOH with
HCl. Acidic phosphatase and urease activity was measured according to Tabatabai
and Bremner (1969), the ß-gluco -and ß-galactosidase by the
method of Serra-Wittling et al. (1995), and the activity of fluoresceine
diacetate by the method of Inbar et al. (1991). Microbial biomass carbon
was estimated following Wu et al. (1990), the nitrobacters were measured
from soil suspensions (Rowe et al. 1977) and the phospholipid profiles were
done according to Zelles et al. (1992).
Results and Discussion
Compost properties
The compost had 713 g
kg-1water
and was acidic (Table 1). Its C:N ratio was 40 which should normally result
in soil N irnrnobilization (Sims 1990). The compost contained 11.3 g kg-1
total N which is in the low range of what is reported for paper mill residues
(AIFQ 1997). Amounts of 745 mg kg-1
NH4+
and 1028 mg kg-1
N03-
were found in soluble forms which was 15.6 % of total N. The molybdate reactive
water-soluble P was 0.24 g kg-1
which was only 8.5 % of the compost total P content. The C:P ratio was 161
which should result in P immobilization (White 1981). The total K content
is very low but well balanced with the total P content. The material had
significant contents of Mn, Zn and Cu in total and soluble forms (Table
1). The content of heavy metals was all below the detection limits and that
for the quality "A" criteria for compost in Canada (Ministe're de l'Environnement
du Québec 1997). The high water-soluble Mn content may be of concern
when the compost is added to very acidic soils (pH <5.3).
Soil chemical composition There was a significant compost-fertilizer
interaction on the pH (CaCl2 0.01 M) 30 days after potato planting
(Figure 1). There was a trend for compost addition to decrease soil pH and
the effect was additive to the impact of fertilizer N on this poorly buffered
soil. Ammonium nitrate had no effect on the soil pH in absence of compost
addition. Also, at 120 Mg ha-1, N
N fertilizer had limited impact on soil pH. At harvest, the soil pH was reduced
by 0.15 units with the application of 150 and 225 kg N ha-1 of
ammonium nitrate and with compost rate of 80 and 120 Mg ha-1. This
acidification originates from the nitrification of the ammonium comprised
in the NH4NO3and also from the mineralization of labile
C compounds in the compost. The compost itself was acidic (Table 1). Cooper
and Warman (1997) reported higher soil pH with chicken manure compost than
with fresh manure or inorganic fertilizers. This type of compost has normally
a higher pH than the compost used in the present study.
The inorganic soil N (NH4+ and N03-) content 30 days after planting was significantly increased by compost addition at 80 Mg ha-1 and more, whereas NH4NO3addition had a lesser effect (Figure 2). Gagnon et al. (1998) reported increases in soil profile inorganic N contents of two soils with the addition of commercial composts. Most of this increase was attributed to the inorganic N contribution of the composts. In the present study, 19kg water- soluble N were provided by each amount of 40 Mg ha-1 compost added.
The amount of inorganic N at harvest was proportional to the amount of NH4NO3added N (Figure 3). Compost rates had no significant impact on residual N in the 0-20 cm layer. Gagnon et al. (1998) observed no significant effect of compost on soil N at fall on a Kamouraska clay. The organic N comprised in the compost should be in very stable forms, so it is not surprising that limited impact on residual N was observed.
The amount of Mehlich-3 extractable P was significantly increased by the compost addition whereas P fertilizer had no such effect (Figure 4). Increases in soil-test P were previously reported with the addition of raw de-inking materials (Norrie and Gosselin 1996, Simard et al. 1998). Neilsen et al. (1998) reported a large increase in soil-test P with the addition of composted biosolids and related that to the P added. The increase in Mehlich-3 extractable P of the 0-20 cm layer with the 80 Mg compost ha-1 was approximately of 40 kg ha-1. An amount of 64 kg total P of which only 6 kg in inorganic form was added with the compost. If we assume that tuber P uptake was around 20 kg ha-1 for a total yield of 40 Mg ha-1, then the efficiency coefficient of the compost P would be close to 100 %. This is very unlikely. A contribution of the soil organic and mineral pools by the action of the compost is more probable. For instance, the observed increase in the Mehlich 3 extractable-P may be related to the impact of compost on enzymes responsible for the mineralization of organic P. Cooper and Warman (1997) had previously shown that compost effect on dehydrogenase activity was related to soil texture. The impact of organic acids/humic substances present in the compost or produced during the decomposition of the compost on the soil P sorption capacity may also have contributed to the increase in soil-test P as suggested by Ohno and Erich (1997) and Iyamuremye et al. (1996).
The amount of Mehlich-3 extractable K was increased by the addition of 200 kg K ha-1 whereas compost had no residual effects on extractable K (Figure 5). Previous studies with raw materials on turfgrass (Norrie and Gosselin 1996) and barley (Simard et al. 1998) have shown increased Mehlich-3 extractable K contents. The difference between these results and those of the present study may be related to the much higher K uptake by the potatoes than by turfgrass or barley, leaving much less residual Kin the soil at harvest. In the present study, only 11.3 kg K ha-1 were added to the soil by each increment of 40 Mg compost ha-1. The K uptake of the potato crop was around 75 kg K ha-1. It is therefore not surprising to observe little impact of the compost on soil-test K. The Mehlich-3 extractable Mg content of the 0-20 cm layer was not significantly influenced (p< 0.05) by the compost addition.
The Mehlich-3 extractable
Pb and Cd contents were not affected by the treatments (data not shown).
The compost used had very low heavy metal content (Table 1), thus it is
not surprising to measure no significant increase in the amounts of Mehlich-3
extractable metals.
Soil microbial activity
The soil biochemical properties
reached their maxima at different time in the growing season. The acidic
phosphatase activity was maximum after the fourth week (Figure 6). The peak
of activity was recorded early in the growing season, at 2 wk after compost
addition for the ß-glucosidase and at 4 wk for the FDA, the 13-galactosidase
and the C-CO2 release in incubation (Figs. 7, 8, 9 and 10). In
spite of lower levels, activities of FDA and P glucosidase remained constant
until the end of the season whereas the activity of ß-galactosidase
reached its lowest point at 8 wk whereas C-CO2 release was lowest
at 12 and 16 wk. Microbial biomass C was highest at 12 wk whereas it was
the lowest at 4 and 20 wk (Figure 11). Urease activity was higher in late
summer and fall (12 to 20 wk) than early in the season (2 and 4 wk) (Figure
12). Finally, the number of nitrobacters (NO2-) tend
to peak earlier with low compost rates (Figure 13). Recent addition of fresh
C source may promote microbial activity. However, the date at which maximum
peak was obtained varied with the enzymes. The various nutrients contained
in the soil and c6mpost are released sequentially by the different enzymes,
depending upon their complexity. To this end, it seems that the availability
of glucose is a primary concern in comparison with galactose early after
paper sludge compost addition.
The 40 Mg compost ha-1 gave the highest values of the selected biochemical properties at every sampling dates. This effect was noted very soon in season (2 wk) for all enzymes with the exception of urease, and for the number of nitrobacters whereas it was later for biomass C (4 wk), urease (8 wk) and C-CO2release (8 wk). The supplement of inorganic fertilizers to compost resulted in higher enzyme activities. It also enhanced nitrobacters, especially at harvest (16 wk). However, it had no effect on C-CO2release and microbial biomass C. However, at 4 wk, their addition to 120 Mg compost ha-1 significantly decreased the microbial biomass C as compared with the unamended treatments. In the present experiment, addition of compost to soil stimulated microbial activity when the rate did not exceed 40 Mg ha-1. Moreover, supplementation of compost with inorganic fertilizers was beneficial, probably counteracting the high C/N and C/P ratios of the compost.
Phospholipid signature
markers indicated the establishment of specific microbial communities in
soil receiving organic amendments when compared to inorganic fertilizers
(data not shown). On the basis of our data, community fatty acid profiles
can be used to assess the relative similarities and differences of microbial
communities. However, detailed interpretation in terms of biomass or taxonomic
composition must be taken with caution until our knowledge of the quantitative
and qualitative distribution of fatty acid profiles over a wide variety
of taxa and the effects of growth conditions on fatty acid profiles is more
advanced.
Tuber marketable yieldsThere was a significant compost rate-NH4NO3interaction on the total and marketable tuber yield (Figure 14). Ignoring the inorganic N input, the best yields were obtained with 40 Mg compost ha-1. Addition of 80 or 120 Mg compost ha-1 decreased tuber yields compared to the treatments when only NH4NO3was added. There was a quadratic response to NH4NO3 in all of the compost rates (Figure 14). An input of 150 kg N ha inorganic fertilizer was best for all compost rates.
There was also a significant
interaction between compost and fertilizer P. In absence of fertilizer P,
80 Mg compost ha-1
produced the highest marketable yield (Figure 15). For the 100 and
200 kg P ha-1, an input
of 40 Mg compost ha-1
produced the highest yields. The 120 Mg compost ha-1
reduced yields compared to the no compost treatment for all P rates except
the 100 kg P ha-'. The positive response of tuber yields to compost addition
is reduced as fertilizer P rate is increased. These results confirm those
of the soil analysis that U clearly showed that compost increased soil test
P and soil enzyme P activity. This resulted in increased P availability
for the potato crop.
Tuber quality
There was a significant
compost-NH4NO3interaction on tuber specific gravity
(data not shown). In absence of NH4NO3, compost decreased
the tuber specific weight. The increase in the amount of compost added in
presence of NH4NO3had the inverse effect, reducing
the negative impact of N fertilizer on specific gravity. The compost addition
did not reduced the soil soluble mineral content of the high inorganic N
fertilizer treatments 30 days after planting (Figure 2). The increase in
tuber specific gravity may therefore be related to a better supply of soil
P or to a factor unidentified by the present experiment.
There was a significant decrease in potato scab index with compost addition (Figure l6). Although this observation is difficult to explain, it may be related to the increase in microbial activity from compost addition which may have suppressed the activity of the scab species. There was no significant effect of the compost .addition on the proportion of tuber showing the "hollow hearth" symptom.
Conclusions
This study indicated that application of compost to this sandy soil, although it had a high organic matter content, may be beneficial to potato tuber yields. The soil inorganic N content was increased 30 days after compost application and so was the amount of extractable P. This indicated that the hypothesis of soil N and P immobilization that was suggested by the C/N and C/P ratio of the compost was not valid in this studied soil. In that sense, excessive compost addition should be avoided since they was not beneficial to tuber yields and soil quality. Compost beneficial effects are normally of short term. As for any other soil amendments, care should be taken to apply the right amount. A larger amount may have been appropriate in a soil with a lower organic matter content. A study conducted in the adjacent part of the field indicated that the beneficial effects of compost are inversely proportional to the soil organic matter content (Cambouris et al. 1997).
We suggested that mixing the raw material with hog liquid manure may help to reduce the immobilization of soil N and the need of complementary inorganic N fertilizer addition to non-leguminous crops (Simard et al. 1998). This may also help to reduce the surplus of manure in some watersheds if the compost is exported to the potato producing areas. The results of the present study suggest that the compost production is a very viable alternative in the management of these two by-products of the forest and agricultural industries. Potatoes are produced on very sandy soils in Québec, and are highly prone to wind and water erosion. Timely addition of compost is probably one of the best ways to maintain or improve their productivity through the input of stable C compounds. The compost is richer in P and K than the raw material and is so less likely to produce nutrient imbalances for the crop. In addition, it meets the "A" criteria for compost; its use on potato production would not be restricted.
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Acknowledgements
This study is supported
by Les Composts du Québec and Agriculture and Agri-Food Canada through
the Matching Industrial Initiative Grant Program. The assistance of Antoine
d'Avignon and Gilles Fortin in the field, of the personnel of the Joseph
Rhéaume farm for evaluating the tuber size and quality, and of Alain
Larouche and Sylvie Michaud in the laboratory is appreciated. We wish to
thank Les Patates Herman Dolbec for providing the site and helping in the
soil preparation and in the spraying of the pesticides.
