SSSAJ Journal of Natural Resources and Life Sciences Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (20)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Agricola
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Related Collections
Right arrow Soil Organic Matter
Right arrow Potato
Right arrow Other Soil Management
Soil Science Society of America Journal 66:1311-1319 (2002)
© 2002 Soil Science Society of America

DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Organic Amendment and Rotation Crop Effects on the Recovery of Soil Organic Matter and Aggregation in Potato Cropping Systems

A. Stuart Grandya, Gregory A. Porter*,b and M. Susan Erichb

a W.K. Kellogg Biological Stn. and Dep. of Crop and Soil Sciences, Michigan State Univ., Hickory Corners, MI 49060-9516
b Dep. of Plant, Soil, and Environmental Sciences, 5722 Deering Hall, Univ. of Maine, Orono, ME 04469-5722

* Corresponding author (porter{at}maine.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 
Soil structural degradation is common in intensively cultivated ecosystems due to the depletion of soil organic matter (SOM). We investigated the mechanisms by which different frequencies of organic amendment application and rotation crops restore C, N, and aggregation in gravelly loam soils used for potato production. A single amendment application [FIRST; 22 Mg ha-1 compost and 45 Mg ha-1 beef cattle (Bos taurus L.) manure] did not affect total C in 1996 and increased it by 28% in 1997 relative to unamended plots (NONE); light fraction (LF) C accounted for 56% of this increase. Plots in which amendment was suspended for 1 yr (SASP) following 4 or 5 yr of annual application had more total C in 1996 (28%) and 1997 (46%) relative to NONE. A green manure crop consisting of oat (Avena sativa ‘Porter’), pea (Pisum sativum ‘Trapper’), and hairy vetch (Vicia villosa Roth) grown in 2-yr rotation with potatoes (Solanum tuberosum L.) increased soil C in 1997 (25.9 vs. 23.9 g kg-1), LF properties in 1996 and 1997, and water soluble carbohydrates (WSC) on several sample dates relative to an oat rotation crop. Large aggregate (2–6.5 mm) stability in 1996 and 1997 and medium aggregate (1–2 mm) stability in 1997 were increased by FIRST relative to NONE. Total soil C was more strongly related to medium (r = 0.65 in 1997) and large (r = 0.51 in 1997) aggregate stability than LF or water soluble carbohydrate fractions. Compost and manure influences occurred rapidly and were persistent, demonstrating that annual applications are not necessary to reverse soil degradation.

Abbreviations: CONT, amendments applied annually for 5 or 6 yr • FIRST, a single amendment application • LF, light fraction soil organic matter • NONE, amendments never applied • SASP, amendment inputs suspended after four or five consecutive years of application • SOM, soil organic matter • WSC, water soluble carbohydrates


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 
POTATOES are Maine's principal agricultural output and are currently produced on {approx}25000 hectares. Rapid declines in SOM concentration and structural stability are typical in potato production systems (Saini and Grant, 1980) and often lead to erosion (Hepler et al., 1983; Kachanoski and Carter, 1999). Frequent soil disturbances, including primary tillage, planting, and intensive cultivation for weed control and harvest aerate the soil and break down aggregates, exposing occluded organic matter (Lal et al., 1994; Six et al., 1999). Potato crops return only {approx}1500 kg ha-1 residue to the soil (Porter and McBurnie, 1996) and the residue has a low C/N ratio (10:1 for potato shoots) and lignin content, which increases its decomposition rate (Bending and Turner, 1999).

One strategy to increase soil structure is to build organic matter pools that facilitate aggregation, such as LF and WSC. Products of LF decomposition include polysaccharides and other materials that stabilize aggregates (Six et al., 1998). Light fraction decomposition may also be an important source of plant nutrients (Wander et al., 1994). Water soluble carbohydrates directly stabilize aggregates (Angers and Mehuys, 1989) and have been strongly correlated (r = 0.74) with aggregation (Haynes and Swift, 1990).

Green manure crops increase soil C inputs, but their effects on SOM equilibrium and aggregation may occur slowly because background levels of soil C are relatively high and spatially variable (Robertson et al., 1993, 2000). Long-term annual compost and manure applications increase SOM and structure (Sommerfeldt et al., 1988; Gilley and Risse, 2000); however, annual applications are expensive (Araji et al., 2001) and thus not widely utilized in Maine. Applying organic amendments less than annually would be more cost effective if they could reverse the negative effects of potato production.

Minimizing the frequency of organic amendment application depends on predicting the number of applications necessary to halt declines in SOM and structure and, once the decline stops and amendments are no longer applied, whether the benefits of amendment persist. Increases in soil C and total aggregation have been reported in potato cropping systems after a single compost and manure amendment application (Porter et al., 1999), but relationships between organic matter pools and aggregation still require elucidation. Effects of organic amendments may last for a century or more on abandoned farm land (Compton and Boone, 2000), but the persistence of their influence on intensively cropped fields with low structural stability is unknown.

In this study, we altered organic amendment treatments in a study originally designed to compare unamended potato cropping systems to long-term annually amended systems (Porter et al., 1999). Our objectives were: (i) to determine if SOM and aggregation could be increased following first-year amendment application and, more importantly, if the beneficial effects of amendments would be retained after annual applications had ceased; (ii) to determine if a productive green manure crop could enhance active SOM components and aggregation relative to the 2-yr cereal grain rotation commonly used in potato systems; (iii) to establish whether soil aggregation was related to soil C and N, LF, and/or water soluble polysaccharides in these differentially managed soils.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 
Site Characteristics
The experiment was conducted at the University of Maine's Aroostook Research Farm in Presque Isle, ME, in 1996 and repeated in 1997. The soil was a Caribou gravelly loam (fine-loamy, isotic, frigid, Typic Haplorthods). Potatoes were grown on two adjacent sites with identical treatment schemes: Site 1 was used for potatoes during 1993, 1995, and 1997; Site 2 was used for potatoes in 1994 and 1996. Rotation crops were planted in alternate years.

Cultural Practices
The potato cultivar planted was ‘Superior’. Potato seedpieces were planted 5 to 7 cm below the soil surface in rows 91 cm apart and at an average within-row spacing of 23 cm. Fertilizer was applied at planting in two bands {approx}5 cm to each side and slightly below the seedpieces. Potassium was applied as KCl, P as diammonium phosphate, and N as diammonium phosphate, ammonium sulfate, and ammonium nitrate. Fertilizer rates (Table 1) were based on soil tests, previous crop, and amendment analysis. Tillage consisted of chisel plowing in the fall, spring disking after compost and manure amendment application, and harrowing before planting. Plots were cultivated once and hilled once during each growing season. Pest control and other management practices were typical of commercial practices in the area.


View this table:
[in this window]
[in a new window]
  		Table 1. Rotation crop management, fertilizer rates, and changes in organic amendment application from 1992 to 1997. Details for the 1992–1995 design are presented in Porter et al. (1999).

 
Experimental Design and Analysis
Prior to 1996, our study plots were used to test the effects of two organic amendment and rotation crop treatments (Table 1) on soil properties and potato yields (Porter et al., 1999). Plots (9.1 by 13.7 m) were arranged as a factorial combination of amendment and rotation crop with four replicate blocks. In the current study, amendment treatments were altered in one half of the experimental plots, resulting in four amendment treatments (Table 1): NONE; FIRST; SASP, amendments last applied in 1995 after four consecutive years of application (Site 2) or in 1996 after five consecutive years of application (Site 1); and CONT, amendments applied annually since 1992 for 5 (Site 2) or 6 yr (Site 1).

Amendments consisted of cull potato compost supplied by a local producer (H. Smith Packing, Westfield, ME) and beef cattle manure (Table 2). The application rate for compost was 22 Mg ha-1 in all years except 1996 when the application rate was 17 Mg ha-1 (dry matter equivalents of 5 and 11 Mg ha-1 in 1996 and 1997, respectively). The application rate for manure was 45 Mg ha-1 cattle manure (dry matter equivalents of 17 and 16 Mg ha-1 in 1996 and 1997, respectively). A disk cultivator was used to incorporate amendments in the spring before potato planting.


View this table:
[in this window]
[in a new window]
  		Table 2. Characteristics of compost and manure amendments applied in 1996 and 1997.{dagger}{ddagger}

 
The two different crop rotations consisted of oats or a legume-based green manure grown in a 2-yr rotation with potatoes. Oats were seeded at a rate of 112 kg ha-1 and received 45 kg N ha-1. The green manure consisted of pea, oats, and hairy vetch seeded as a mixture at rates of 112, 54, and 34 kg ha-1, respectively. The green manure was inoculated with Rhizobium before seeding and received no fertilizer. Oat straw and green manure were incorporated using a chisel plow in the fall.

Analysis of variance was performed using a factorial randomized complete block design with four levels of amendment and two levels of rotation crop. Amendment and rotation crop effects were analyzed separately for each year because of treatment x year interactions and because the histories of amendment application to Sites 1 and 2 were different. Statistical differences between amendment means were determined using Fisher's LSD at P < 0.05.

Rotation Crop and Amendment Sampling
Quadrat samples (0.5 m2 each) were collected from each oat and green manure plot to determine total aboveground biomass production. Oat straw yield was estimated from the difference between grain (determined using a small-plot combine) and total biomass samples. The oat crop planted prior to the 1997 potato crop was not harvested due to unfavorable weather, so the total aboveground biomass was used to determine biomass contributions to the soil.

Rotation crop N content was determined in 16 green manure plots in 1997 and 16 oat plots in 1996 and 1997. In 1996, the N content of the green manure was determined in eight plots. In 1997, a subsample of the unsorted, pooled sample from eight green manure and eight oat plots was analyzed for C. The two residue types had statistically equal C levels (t-test, P < 0.05). The pooled mean (44.4%) was used as the C value for all rotation crop samples in 1996 and 1997 to determine the C contribution to the soil by the rotation crops.

Compost and manure samples were taken in triplicate prior to amendment application in the spring and analyzed for C, N, pH, and KCl-extractable NH+4 (Griffin et al., 1995). Nutrient analysis was conducted by inductively coupled plasma atomic emission spectrometry using a method adapted from Kalra and Maynard (1991).

Soil Sampling and Analysis
Soil used in WSC and aggregate analyses was collected with a trowel to a depth of 15 cm three times each year: (i) before spring tillage and amendment application (May); (ii) after amendment application but before the first hilling (June); and (iii) before harvest (September). Ten subsamples per plot were taken with care to avoid plot edges and rows used for implement traffic and then composited. Soil collected in June of each year was also analyzed for C, N, and LF. Soil used for aggregate analysis was dried in paper bags at 26°C; soil used for other analyses was spread thinly on plastic on a greenhouse bench and stirred periodically until dry. Depending on the analysis conducted, dry soil was sieved to <0.5 mm (WSC, C and N), <2 mm (LF), or <6.5 mm (aggregates).

Two bulk density samples were taken in each plot to the depth of the Ap horizon (23 cm) in July 1996 and August 1997. Bulk density was calculated using the volume of the coring device and oven-dry weight of the soil after correcting for coarse fragments >2 mm (Blake and Hartge, 1986). There were no significant effects of amendment or rotation crop on soil bulk density (Table 3), so C and N data are presented on a gravimetric basis. Prior to amendment application in the spring, samples were taken (23 cm) for soil mineral analysis, dried, sieved (<2 mm) and subsequently analyzed by the University of Maine Soil Testing Service using standard methods (Hoskins, 1997).


View this table:
[in this window]
[in a new window]
  		Table 3. Amendment and rotation crop effects on soil bulk density in 1996 and 1997.{dagger}{ddagger}

 
Soil Carbon, Nitrogen, and Organic Matter Fractions
Light fraction organic matter was separated using methods developed by Strickland and Sollins (1987). Fifty milliliters of NaI with a density of 1.7 g cm-3 was added to 25 g of soil in a 100-mL centrifuge tube. Shaking for 45 min on a wrist-action shaker dispersed the samples and the heavy fraction was separated out by centrifugation at {approx}1070 g for 1 h. The LF was aspirated from the surface of each sample into a vacuum flask and then washed with at least 150 mL of 0.01 M CaCl2 followed by at least 200 mL of deionized water. The LF was dried at 70°C for 24 h.

Water soluble carbohydrates were determined colorimetrically using anthrone sulfuric acid reagent (Grandy et al., 2000). Soils were incubated in an oven for 24 h at 85°C using a soil: water ratio of 1:10 (w/v). Solutions were vacuum filtered through 0.3 µm glass filters, reacted with anthrone sulfuric acid reagent, and absorbance was read at 625 nm using a Spectronic 1001 (Milton Roy Co., Rochester, NY). A solution consisting of deionized water and anthrone was used as the blank.

Total C and N concentrations of the soil, LF, organic amendments, and rotation crops were measured by combustion (CN-2000, Leco Corp., St. Joseph, MI). The low pH (Table 4) in these plots and time since the last lime application (spring, 1992) indicate that there was little carbonate present in the soil; therefore, the total soil C measured likely originated from organic C.


View this table:
[in this window]
[in a new window]
  		Table 4. Rotation and amendment effects on general soil chemical properties in 1996 and 1997, prior to start of FIRST [Amendments applied only in 1996 (Site 2) and 1997 (Site 1)] and SASP [Amendments last applied in 1995 (Site 2) or 1996 (Site 1) after application since 1992] treatments.

 
Water Stable Aggregates
Aggregates were obtained by a modification of the wet-sieving method developed by Yoder (1936) and more recently described by Porter et al. (1999). Briefly, a nest of screens with descending mesh size was used to separate aggregates into three size classes: 2 to 6.5 mm (large), 1 to 2 mm (medium), and 0.25 to 1 mm (small). A 25-g sample was completely immersed in water for 10 min on the uppermost sieve, followed by oscillation for 10 min at 35 oscillations min-1. After sieving, the sample collected on each sieve was washed into beakers, oven dried, and weighed. Sand content was determined following dispersion in sodium hexametaphosphate.


   RESULTS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 
Amendment and rotation crop C and N contributions to the soil are presented only for 1997 (Fig. 1) because the C content of the manure and compost amendments was not available for previous years. Amendments contributed {approx}1.8 times more C to the soil than either rotation crop and {approx}1.8 and 2.8 times more N than the green manure and oat rotation crops, respectively. In 1997, the C contributions from the two rotation crops were similar because the oat crop was not harvested the previous fall. The green manure contributed greater N to the soil than the oats (P < 0.01) and increased the C/N ratio (9.95 green manure vs. 9.01 oats; P < 0.01) of the soil (data not shown). In 1996, the green manure contributed more C (2600 vs. 1100 kg ha-1) and N (137 vs. 40 kg ha-1) than oats (data not shown). Soil bulk density was not significantly affected by amendment or rotation crop (Table 3).



View larger version (24K):
[in this window]
[in a new window]
  		Fig. 1. Amendment (compost and manure) and rotation crop C and N contributions to the soil in 1997.

 
Soil mineral analysis was done in the spring before imposition of the altered amendment treatments (FIRST and SASP), so comparisons among two amendment (NONE vs. CONT) and the rotation crop programs are relevant (Table 4). As a result of the high levels of P, K, Mg, and Ca in the amendments (Table 2), concentrations of these nutrients were all significantly increased by amendment application.

Soil Carbon, Nitrogen, Light Fraction, and Water Soluble Carbohydrates
In 1996 FIRST and NONE had equal C contents, and in 1997 FIRST increased soil C by 28% (Fig. 2) . Amendments applied annually for 5 or 6 yr increased total soil C by 23% relative to SASP in 1996, but there were no significant differences between these treatments in 1997. More C was present in SASP compared with NONE soils in both 1996 (28%) and 1997 (46%). Total soil N was statistically equal in FIRST and NONE, and in CONT and SASP, in both years of the study (Fig. 2). SASP resulted in more N than NONE in 1996 (23%) and 1997 (22%). Rotation crop had no effects on total soil N in either year or on total soil C in 1996 (data not shown). In 1997, the green manure crop resulted in higher soil C (P < 0.05) than the oat rotation crop (25.9 vs. 23.9 g kg-1).



View larger version (45K):
[in this window]
[in a new window]
  		Fig. 2. Amendment (compost and manure) effects on soil: (a) C, and (b) N. Amendment treatments: NONE, no amendments applied; FIRST, amendments applied only in 1996 (Site 2) or 1997 (Site 1); SASP, amendments last applied in 1995 (Site 2) or 1996 (Site 1) after application since 1992; and CONT, continuous amendment application since 1992. Means followed by the same letter within years are statistically equal (P < 0.05) using Fisher's LSD.

 
Single amendment applications increased all LF properties in 1996 and 1997 relative to NONE (Tables 5 and 6). All LF properties were increased by CONT relative to SASP in 1996 (except for N concentration) and 1997, and were greater in SASP than NONE in 1996 (except for N concentration) and 1997. The green manure crop increased LF N concentration, total LF N in the soil, and the percentage of total soil C and N in the LF in 1996. In 1997, the green manure crop increased all LF properties except the percentage of total soil C in the LF.


View this table:
[in this window]
[in a new window]
  		Table 5. Amendment and rotation effects on selected properties of the soil light fraction (LF) in 1996.

 

View this table:
[in this window]
[in a new window]
  		Table 6. Amendment and rotation effects on selected properties of the soil light fraction (LF) in 1997.

 
The May carbohydrate and aggregate samples were collected before imposition of the revised amendment treatments, so we expected that CONT and SASP would be equal because these plots had the same treatment history, and that NONE and FIRST would be equal but lower than the other two. In May 1996, WSC in FIRST was lower than in NONE, and WSC in CONT was higher than in SASP. Consequently, we were not able to detect greater WSC in FIRST relative to NONE during June or July, or decreases in SASP compared with CONT at these dates (Fig. 3a) .



View larger version (41K):
[in this window]
[in a new window]
  		Fig. 3. Amendment (compost and manure) effects on soil water-soluble carbohydrates: (a) 1996 and (b) 1997. Amendment treatments: NONE, no amendments applied; FIRST, amendments applied only in 1996 (Site 2) or 1997 (Site 1); SASP, amendments last applied in 1995 (Site 2) or 1996 (Site 1) after application since 1992; and CONT, continuous amendment application since 1992. The May sample was taken before imposition of the altered amendment treatments. Data were analyzed separately for each sample date. Means followed by the same letter within sample dates are statistically equal (P < 0.05) using Fisher's LSD.

 
In 1997, FIRST resulted in greater WSC than NONE on the June and September sampling dates (Fig. 3b). There were no differences between CONT and SASP, and SASP maintained higher WSC than NONE. Green manure resulted in significantly greater WSC than oats in June 1996 (7%, P < 0.05), June 1997 (8%, P < 0.05), and September 1997 (20%, P < 0.01) (data not shown). The differences were not significant on the other three sampling dates.

Soil Aggregation
In 1996, there were no amendment effects on the small aggregate content in the soil (Fig. 4) . The medium aggregate content of the soil in June was not affected by amendment addition. In September, the content of medium aggregates in CONT was significantly higher than in SASP, and in SASP relative to NONE. In September 1996, the large aggregate content of the soil was greater in FIRST than NONE, in CONT than SASP, and in SASP than NONE.



View larger version (35K):
[in this window]
[in a new window]
  		Fig. 4. Amendment effects on soil aggregates in 1996: (a) small (0.25–1.0 mm); (b) medium (1.0–2.0 mm); and (c) large (2.0–6.5 mm). Amendment treatments: NONE, amendments never applied; FIRST, amendments applied for the first time in 1996; SASP, amendments last applied in 1995 after application since 1992; and CONT, amendments applied since 1992. The May sample was taken before imposition of the altered amendment treatments. Means within a year and sample date followed by the same letter are statistically equal (P < 0.05) using Fisher's LSD test. No grouping letters are presented for sample dates that had a nonsignificant (P < 0.05) F-test for treatment effects.

 
In May 1997, the content of small aggregates was greater in SASP than in CONT (Fig. 5) . In June and September, all four treatments were statistically equal, indicating a relative decrease in SASP, increase in NONE, and no differences between FIRST and NONE. In June and September, the content of medium aggregates in the soil was statistically greater in FIRST relative to NONE. There were no significant differences in medium aggregate content between CONT and SASP; SASP retained higher aggregate content than NONE. Single amendment applications increased the content of large aggregates in the soil relative to NONE in September. Large aggregate content of the soil was equal in CONT and SASP, and higher in SASP than NONE, on all sampling dates.



View larger version (36K):
[in this window]
[in a new window]
  		Fig. 5. Amendment effects on soil aggregates in 1997: (a) small (0.25–1.0 mm); (b) medium (1.0–2.0 mm); and (c) large (2.0–6.5 mm). Amendment treatments: NONE, amendments never applied; FIRST, amendments applied for the first time in 1997; SASP, amendments last applied in 1996 after application since 1992; and CONT, amendments applied since 1992. The May sample was taken before imposition of the altered amendment treatments. Means within a year and sample date followed by the same letter are statistically equal (P < 0.05) using Fisher's LSD test. No grouping letters are presented for sample dates that had a nonsignificant (P < 0.05) F-test for treatment effects.

 
There were no significant rotation crop effects on aggregation in 1996 (P < 0.05). In 1997, green manure increased medium aggregates compared with oats in May (4.98 vs. 3.94%) and June (5.51 vs. 4.67%, by weight). Large aggregates were also increased by green manure in May (7.58 vs. 5.25%) and June (9.86 vs. 7.85%, by weight) (data not shown).


   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
SUMMARY AND CONCLUSION
 REFERENCES
 
Total soil C increases in FIRST in 1997 are consistent with previous work (Porter et al., 1999), demonstrating that a single organic amendment application at high rates can prevent additional SOM losses and soil structure degradation. Light fraction C accounted for 56% (by weight) of the soil C increase in FIRST. Changes in C and N concentrations of the LF in FIRST should increase the ability of this SOM pool to supply plant nutrients and provide habitat for microorganisms (Wander et al., 1994).

Differences in total C between SASP and CONT in 1996 could largely be accounted for by declines in LF C; 67% of the 5.9 g kg-1 C deficit in SASP was due to differences in LF C. Converting forest soils and grasslands to cultivated agriculture often results in a rapid decline in C as microbes degrade highly labile material (Giddens, 1957) such as LF. In our studies, the short duration of amendment application in the CONT plots resulted in the accumulation of a large proportion of labile materials, rather than humic substances, that are rapidly decomposed in intensive potato cropping systems. This is indicated by the high percentage of total soil C in the LF (29.5% in 1996 and 32.6% in 1997). In comparison, Bremer et al. (1994) found that LF accounted for 9 to 24% (by weight) of soil organic C and Biederbeck et al. (1998) found that the LF as a proportion of soil organic C ranged from 9.5 to 11.4% for different cropping systems. Enhancing the conservation of LF through tillage reduction or other strategies would increase C retention in the amended systems.

Declines in the percentage of total soil C in the LF with decreasing organic matter inputs suggest that the rate of C decline in SASP should slow down in subsequent years (Hyvönen et al., 1998). This is also supported by changes in LF quality in SASP relative to CONT; SASP LF had a lower C concentration than CONT in 1996 and 1997, and lower N content in 1997. Light fraction materials with a high C and N content in SASP were likely the most rapidly colonized and decomposed substrates, and their decline should result in slower mineralization rates.

Differences between SASP and NONE indicate that the benefits of amendment application on total soil C and LF persisted for at least one growing season after amendment application ceased. Eventually, a new equilibrium between inputs and losses of organic materials will be achieved, which may have greater C than plots that never received amendments (Jenkinson and Rayner, 1977; Sommerfeldt et al., 1988).

Greater C contributions from the green manure relative to oats since 1992 (except in 1997) likely explain soil C increases in 1997 and changes in LF in 1996 and 1997. Additionally, the green manure residue had a low C/N ratio which may have enhanced its sequestration within aggregates (Drinkwater et al., 1998); evidence for this is that the green manure increased medium and large aggregates in 1997. Relatively high and spatially variable background levels of soil C likely caused the lack of an effect in 1996 and relatively small differences in 1997. More time may be necessary for the soil C effects of the green manure rotation crop to become more consistent. Similarity of N among rotation crops and amendment treatments may be due to the addition of more N fertilizer to unamended potato plots and in the oat rotation compared with the green manure rotation.

Organic materials stabilizing the small aggregates appeared to be different from those stabilizing the larger aggregate size classes. In contrast to medium and large aggregates, small aggregates did not change in response to FIRST or SASP, and were generally not correlated with soil C, N, and LF properties (Table 7). Models of aggregate formation and stabilization typically separate aggregates into two classes: microaggregates (<250 µm) are stabilized by clay-polyvalent cation-humic substance complexes and are relatively resistant to short-term changes in soil management; macroaggregates (>250 µm), stabilized by roots, fungal hyphae, and polysaccharides, are more transient and sensitive to short-term treatment effects than microaggregates (Tisdall and Oades, 1982; Haynes and Beare, 1996; Jastrow et al., 1996). The small aggregates in our study, which are only slightly larger than microaggregates, may be stabilized by humic substances or other stable organic fractions that are unaffected by short-term changes in soil management. Several years may be necessary before changes in organic matter inputs alter organic matter fractions that stabilize small aggregates.


View this table:
[in this window]
[in a new window]
  		Table 7. Correlations of small, medium, and large aggregates with soil C, N, light fraction (LF), and water soluble carbohydrates (WSC).

 
It was expected that WSC, because of their rapid production after C additions to soil, would be involved in aggregate stabilization. Studies investigating management-induced, short-term changes in soil structure have found strong correlations (r = 0.74) between aggregation and soil carbohydrates (Haynes and Swift, 1990). Although there were significant correlations between WSC and small and medium aggregates in 1997, our results suggest that there may be factors or organic matter fractions more closely related to macroaggregation than is WSC. Others have suggested that microbial biomass C or fungal hyphae may exert major effects on macroaggregation (Bethlenfalvay and Barea, 1994; Degens et al., 1994). Previous work in these plots showed that amendment applications significantly increased root length density and root growth (Porter et al., 1999). Some of the increase in aggregation may have been due to physical entanglement of soil particles with roots and production of plant mucilages (or products of their degradation) that directly stabilize aggregates (Perfect et al., 1990; Haynes and Beare, 1996).


   SUMMARY AND CONCLUSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
REFERENCES
 
Our study indicates that recovery of organic matter pools and aggregation can occur in intensively managed Maine potato production systems with compost and manure application less frequently than annually. FIRST effects on medium and large aggregates demonstrate that soil structural improvements may occur quickly. However, slow changes in small aggregates, which represent the majority of aggregated soil in this study, in response to altered organic inputs suggests that several consecutive annual amendments may initially be necessary. Persistence of SOM and soil structure in SASP provides evidence that once soil improvements occur, periodic amendment applications should maintain them.

Light fraction represented a high proportion of total C in amended plots and changed rapidly with changes in organic amendment frequency. One way to maximize the effects of amendment application would be to facilitate the stabilization of this organic matter pool. Enhancing soil aggregation by minimizing soil disturbance could increase the physical protection of LF and thus increase its residence time in the soil (Six et al., 1999).

Rotation crop effects were generally small compared with amendment effects, but changes in total C (1997) and LF indicate that green manure crops may be used as part of a soil management program intended to reverse soil degradation. Reducing the frequency of potatoes in the rotation or including a perennial forage may have greater effects on soil C pools and structure than the green manure used here (Perfect et al., 1990; Angers et al., 1999).


   ACKNOWLEDGMENTS
 
We thank W.B. Bradbury, B. MacFarline, and J.A. Sisson for their technical assistance. W. Halteman is gratefully acknowledged for providing advice about the experimental design and statistical analysis of the experiment. We greatly appreciate the helpful comments provided by the reviewers of this paper and L.M. Zibilske for his insightful comments throughout the study. We also acknowledge H. Smith Packing, Inc. of Westfield, ME, for providing the waste potato compost used in these studies.

Research supported by USDA-CSREES Special Grants for Potato Research (94-34141-0040), the University of Maine Potato Ecosystem Project, Northeast SARE/ACE Grant LNE93-36/ANE93.18, McCain Foods Ltd., and the Maine Potato Board.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 
Maine Agric. & Forest Exp. Stn. Publ. No. 2543.

Received for publication March 9, 2001.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 SUMMARY AND CONCLUSION
 REFERENCES
 




This article has been cited by other articles:


Home page
 Soil Sci.Home page
J. Nyiraneza and S. Snapp
Integrated Management of Inorganic and Organic Nitrogen and Efficiency in Potato Systems
Soil Sci. Soc. Am. J., August 9, 2007; 71(5): 1508 - 1515.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
E. B. Mallory and G. A. Porter
Potato Yield Stability under Contrasting Soil Management Strategies
Agron. J., March 12, 2007; 99(2): 501 - 510.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
A. S. Grandy, G. P. Robertson, and K. D. Thelen
Do Productivity and Environmental Trade-offs Justify Periodically Cultivating No-till Cropping Systems?
Agron. J., October 3, 2006; 98(6): 1377 - 1383.
[Abstract] [Full Text] [PDF]

Home page
 J. Environ. Qual.Home page
A. S. Grandy, T. D. Loecke, S. Parr, and G. P. Robertson
Long-term trends in nitrous oxide emissions, soil nitrogen, and crop yields of till and no-till cropping systems.
J. Environ. Qual., July 1, 2006; 35(4): 1487 - 1495.
[Abstract] [Full Text] [PDF]

Home page
 Soil Sci.Home page
A. S. Grandy and G. P. Robertson
Aggregation and Organic Matter Protection Following Tillage of a Previously Uncultivated Soil
Soil Sci. Soc. Am. J., June 21, 2006; 70(4): 1398 - 1406.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
G. M. McAndrews, M. Liebman, C. A. Cambardella, and T. L. Richard
Residual Effects of Composted and Fresh Solid Swine (Sus scrofa L.) Manure on Soybean [Glycine max (L.) Merr.] Growth and Yield
Agron. J., June 5, 2006; 98(4): 873 - 882.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (20)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Agricola
Right arrow Articles by Grandy, A. S.
Right arrow Articles by Erich, M. S.
Related Collections
Right arrow Soil Organic Matter
Right arrow Potato
Right arrow Other Soil Management

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome