Effect of Nitrogen Fertilizer Application on Growing

TECHNICAL REPORTS: ATMOSPHERIC POLLUTANTS & TRACE GASES

Effect of Nitrogen Fertilizer Application on Growing Season Soil Carbon Dioxide Emission in a Corn–Soybean Rotation Mahdi M. Al-Kaisi,* Marc L. Kruse, and John E. Sawyer Iowa State University Nitrogen application can have a significant effect on soil carbon (C) pools, plant biomass production, and microbial biomass C processing. The focus of this study was to investigate the short-term effect of N fertilization on soil CO2 emission and microbial biomass C. The study was conducted from 2001 to 2003 at four field sites in Iowa representing major soil associations and with a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation. The experimental design was a randomized complete block with four replications of four N rates (0, 90, 180, and 225 kg ha−1). In the corn year, seasonlong cumulative soil CO2 emission was greatest with the zero N application. There was no effect of N applied in the prior year on CO2 emission in the soybean year, except at one of three sites, where greater applied N decreased CO2 emission. Soil microbial biomass C (MBC) and net mineralization in soil collected during the corn year was not significantly increased with increase in N rate in two out of three sites. At all sites, soil CO2 emission from aerobically incubated soil showed a more consistent declining trend with increase in N rate than found in the field. Nitrogen fertilization of corn reduced the soil CO2 emission rate and seasonal cumulative loss in two out of three sites, and increased MBC at only one site with the highest N rate. Nitrogen application resulted in a reduction of both emission rate and season-long cumulative emission of CO2–C from soil.

Copyright © 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Published in J. Environ. Qual. 37:325–332 (2008). doi:10.2134/jeq2007.0240 Received 14 May 2007. *Corresponding author ([email protected]). © ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA

I

ncreased levels of atmospheric CO2 have prompted research assessing the contributions of industrial, agricultural, and environmental practices to current and potentially continued increasing levels of CO2. Various management practices on agriculture land can have an impact on soil C content. Agricultural practices that affect soil C include tillage system, cropping system, N fertilization, and many other practices. It is estimated that soil contains approximately 1.4 × 1012 Mg of C in organic matter and surface litter (Schlesinger, 1991). One of the pathways to lose soil C in a row cropping system as a result of management practices (i.e., tillage, N fertilization, etc.) is the emission of CO2 from soil. This soil C loss mechanism as affected by management practices can be determined and quantified by either measuring CO2 emission or through other indicators such as change in soil microbial biomass C or change in soil C fractions. Generally, sources of CO2 from a soil system can be attributed to biological and chemical activity within the soil. Soil respiration involves organisms metabolizing substrates producing CO2 within the soil matrix (Anderson, 1982). Carbon dioxide loss from soil can also be associated with microbial decomposition of organic matter and root respiration (Witkamp and Frank, 1969; Edwards et al., 1970; Fritz et al., 1978; Singh and Gupta, 1977; Hanson et al., 2000). The mechanism of soil CO2 emission to the atmosphere, however, involves the movement of CO2 through soil pores, and release from the soil system can be measured at the soil surface (Rolston, 1986). Factors such as soil temperature, soil moisture, cropping system, and N availability can all influence soil microbes and their activity. Previous research has shown inconsistent results, particularly in the case of N fertilization effect, on soil microbial biomass and CO2 emission. Kowalenko et al. (1978) found that soils fertilized with N demonstrated low soil CO2 emission in both field and laboratory studies, but those results were contrary to the findings by Willson et al. (2001), where N fertilization had no influence on soil microbial biomass in a corn–soybean rotation. Others have argued that soil microbial activity may increase due to N fertilization as a result of increased plant biomass production, which on incorporation, stimulates soil biological activity (Dick, 1992); or N fertilization reduces microbial biomass due to lowering soil pH (Smolander et al., 1994; Ladd et al., 1994). The inconsistency in N fertilization effects on soil CO2 emission in these field and laboDep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010. M.L. Kruse, formerly graduate student. Abbreviations: CO2, carbon dioxide; MBC, microbial biomass carbon; V6, sixth-leaf stage of corn.

325

Table 1. Soil properties and classification of study sites. Site

Soil series

Organic matter†

Soil pH†

STP†

−1

STK†

Bulk density

−1

Soil classification

−3

g kg —–mg kg —– g cm Boone Clarion 44 6.0 19 110 1.4 Fine-loamy, mixed, superactive, mesic Typic Hapludolls Floyd Clyde 92 6.4 32 115 1.2 Fine-loamy, mixed, mesic Typic Hapludolls Tama Tama 37 6.7 49 190 1.5 Fine-silty, mixed, mesic Typic Argiudolls Warren Nevin 39 6.1 25 209 1.3 Fine-silty, mixed, mesic aquic Argiudolls † Routine soil tests from 0- to 15-cm soil depth samples collected before planting. Organic matter determined by dry combustion using LECO-CHN 2000 analyzer and pH determined using 1:1 soil/water ratio. STP is soil test P determined by Mehlich-3 P and STK is soil test K by ammonium acetate.

ratory studies demonstrates the challenge in understanding the effect of N fertilization on soil C dynamics and loss as CO2. Decomposition of plant residue and soil organic matter is influenced by soil moisture and soil temperature, which also affect plant growth and subsequently soil biological processes. The role of soil moisture in soil CO2 emission as an indicator of C loss is not well defined. Kowalenko et al. (1978), Paul et al. (1999), and Bajracharya et al. (2000) reported that soil moisture alone had no strong effect on CO2 emission. It is most likely that soil moisture coupled with soil temperature and other soil-atmospheric interactions have a great effect on CO2 emission from soil (Pietikäinen et al., 2005). The hypothesis for this research is that increasing N fertilizer application rate for corn production can increase soil CO2 emission and increase soil microbial biomass.

Materials And Methods Site Description This study was conducted from 2001 to 2003 in producers’ fields having a history of a corn–soybean rotation in conservation tillage systems. The four sites in this study were in Boone, Floyd, Tama, and Warren counties in Iowa. The four locations represent four major soil associations. Site characteristics are summarized in Table 1. Planting, tillage operations, and pest control applications were conducted by the cooperating producers. All field measurements were performed by the research team. The plot size for each treatment was 15.2 m long by 4.6 m wide and the plots were located at an easily accessible area of the field. The experimental design was a randomized complete block with four replications. Nitrogen treatments were applied by hand broadcasting dry ammonium nitrate (NH4NO3) to the soil surface for each N rate just after corn emergence (2001 and 2003). The fertilizer N was not incorporated into the soil. The N rates used in this study were 0, 90, 180, and 225 kg N ha−1. Nitrogen treatments were not applied in the soybean production year (2002).

Planting dates, plant populations, and tillage operations are summarized in Table 2. The Warren site was used only for 2 yr, 2001 for corn and 2002 for soybean, and was abandoned in 2003 due to misapplication of anhydrous-ammonia in the fall of 2002 across all plots. The Tama site was used only in 2003, but had the same N applications and rotation as the other sites.

Field Carbon Dioxide Emission Measurements The soil CO2 emission measurements were taken in 2002 when soybean was grown and in 2003 when corn was grown. The measurements started in the spring of 2002 (sites were planted to soybean), which was the year after N rate treatments had been applied to the previous corn crop in 2001. Carbon dioxide emission measurements were taken on the Warren site in 2002 only, the Boone and Floyd sites in 2002 and 2003, and the Tama site in 2003 only. Measurements began immediately after plant emergence each year, were completed at harvest in the fall of 2002 and continued until approximately 1 mo after harvest in the fall of 2003 as weather conditions permitted. The CO2 measurements were collected during the daytime only due to the limitation of the automated CO2 monitoring system availability. Five polyvinyl chloride (PVC) rings, 10 cm in diameter and 5 cm in height, were randomly placed and pressed 3 cm into the soil in each N rate treatment. The PVC rings were placed shortly after crop emergence. The five rings per plot were kept in the same location throughout the growing season and for the duration of CO2 emission measurements. The random placement resulted in rings placed both in rows and between rows. Carbon dioxide emission was measured using a LICOR-6400 (LICOR Inc., Lincoln, NE) infrared gas analyzer approximately every 7 to 10 d between 1000 and 1200 h. Before measuring soil CO2 emission, the ambient CO2 level was determined by leaving the chamber open sideways in an unobstructed area near the PVC ring until the registered reading of ambient CO2 concentration by the LICOR-6400 was stable. The CO2 emission rates were measured in μmol m−2 sec−1. The CO2 emission rate values from all five PVC rings in each N rate treatment were averaged to determine the emission rate. Both soil temperature

Table 2. Planting date, plant population, and tillage operation for the soybean and corn production years. Site

Soybean planting date Soybean population Corn planting date

Boone

9 May 2002

seed ha−1 450,000

Floyd Tama Warren

28 May 2002 14 May 2002 4 May 2002

445,000 420,000 371,000

326

Corn population

26 Apr. 2003

plant ha−1 77,000

29 Apr. 2003 23 Apr. 2003 28 Apr. 2001

84,000 73,000 73,000

Tillage operation for corn and soybean years Field cultivation before corn and chisel plow before soybean. No-tillage with both crops No-tillage with both crops No-tillage with both crops

Journal of Environmental Quality • Volume 37 • March–April 2008

(°C) and volumetric soil moisture (cm3 cm−3) were measured outside the PVC rings concurrently during the soil CO2 emission measurements in the top 5 cm of soil surface using a thermometer unit attached to the LICOR-6400 and a TRIME-FM (Mesa Corporation, Medfield, MA) time domain reflectometry (TDR) system. Carbon dioxide emission data was downloaded into an Excel spreadsheet from the LICOR-6400 using the WinFX program included in the LICOR-6400 software package. Carbon dioxide emission rates were converted from μmol m−2 sec−1 to kg ha−1 d−1. Cumulative soil CO2 emissions as a function of time throughout the growing season were calculated as follows: n

Cumulative CO 2 (t ) = ∑ i

X i + X i +1 ⋅ (t i +1 − t i ) 2

where Xi is the first week CO2 measurement and Xi+1 is the following week CO2 measurement at times ti and ti+1, respectively; and n is the final week of CO2 measurement during the study period.

Microbial Biomass Measurements Soil samples for MBC determination were collected in June 2003 from the four N rate treatments used for CO2 emission measurements when corn reached the V6 growth stage (Ritchie et al., 1993). A composite sample of the 0 to 15 cm of soil from each treatment within each replication was collected and placed in a 3.75-L plastic bag, placed in a cooler at 4°C, and kept at field moisture content. Soil samples were removed from the cooler and sieved through an 8-mm and then a 4-mm sieve. Soil samples were prepared immediately for fumigation and inorganic N extraction to minimize any changes to the microbial populations due to removal and transport from the field environment. Microbial biomass C was determined within 24 h of soil sample collection using the procedure described by Horwath and Paul (1994). Fifty g moist soil samples were fumigated with ethanol-free CHCl3 for 24 h in a Labconco vacuum desiccator (Kansas City, MO). Both fumigated and non-fumigated soil samples were extracted with 100 mL of 0.5 mol L−1 K2SO4 and then filtered through Whatman No. 42 filter paper (Whatman International Ltd., Maidstone, UK). The extractant alone was also filtered to determine the background level of C in the filter paper and extractant. Carbon recovered in the extract was determined with a Shimadzu TOC-5050 C analyzer (Rydalmere, New South Wales, Australia). Microbial biomass C was calculated on an oven dry soil weight basis.

Soil Incubation A laboratory incubation experiment was conducted to measure microbial activity in the same soil samples collected from the Boone, Tama, and Floyd sites for MBC analysis. The soil incubation procedure (Zibilske, 1994) was conducted using soils that were passed through a 2-mm sieve and air-dried. Twenty g of air-dried and sieved soil was weighed into 20 mL borosilicate vials. Approximately, seven g of water were added to the 20 g of soil to bring the soil up to 60% water-filled pore space. Soils were not preincubated before conducting this procedure. Each vial with soil was

placed inside a 0.9-L wide-mouth glass jar (Mason jar) along with a 10-mL scintillation vial containing 1.0 mL of 2 mol L−1 NaOH. Approximately 3 to 5 mL of water was added to the bottom of the glass jar. The Mason jars were closed with lids to completely seal the contents from the outside atmosphere. The Mason jars were then placed in an incubation room at 30°C. The scintillation vials containing NaOH solution were titrated with 1 mol L−1 HCl at 1, 3, 5, 7, 14, 21, 28, 35, 42, 49, and 56 d of soil incubation. Inorganic N (NO3–N and NH4–N) was determined before and after 56 d of incubation using KCl extraction (Mulvaney, 1996). Approximately, 10 g of air-dried soil was placed in a 125 mL Nalgene bottle along with 50 mL of 2 mol L−1 KCl. The Nalgene bottles were placed on an Eberbach shaker for 30 min and after that the extraction solution was filtered though Whatman No. 42 filter paper into 20-mL scintillation vials. The filtered solution was stored in a –4°C freezer until analyses for NO3–N and NH4–N with a Lachat QuickChem 8000 FIA+ (Lachat Instruments, Milwaukee, WI). Net N mineralized was calculated by subtracting the initial inorganic N from that measured at the end of the soil incubation period.

Statistical Analysis Data were analyzed using the Statistical Analysis System package (SAS Institute, 2003). Soil CO2 emission rates in response to N rate were analyzed using Proc MIXED and repeated measurement procedures, where sample collection date was treated as a nonrandom variable over time. Similarly, soil CO2 emission differences between N rates in the laboratory incubation were analyzed using the PROC GLM for each measurement date. The GLM procedure was also used to analyze N mineralization and microbial biomass response to N rate. Cumulative CO2 emissions data over the growing season were analyzed using the GLM procedure. Significant differences were determined at p = 0.05.

Results And Discussion Carbon Dioxide Emission from Soil during Soybean Production The effect of prior year N fertilizer application rate for corn on CO2–C emission from soil was examined in the soybean crop year (2002). The CO2–C emission in situ may include CO2–C from soil organic matter and crop residue decomposition, and root respiration. In this discussion we will refer to CO2–C regardless of the source as soil CO2–C. The immediate effect of the prior-year N rate on soil CO2–C emission during the soybean year at each site is summarized in Fig. 1. Across all sites the soil CO2–C emission rate peaked during the most active soybean growth stage, 60 to 80 d after planting, which may indicate greater root respiration and thus more CO2 contribution. Generally, different N rates had no significant effect on CO2–C emission rate, except on a few days at each site. The peak in CO2–C emission rate appeared to be highly related to soil moisture and temperature conditions. The progressive increase in soil temperature and soil moisture content led to increased CO2–C emission rates. The residual effect of N applied in the corn phase had no lasting effect on CO2–C emission during

Al-Kaisi et al.: Effect of N Fertilizer on Soil CO2 Emission in Corn–Soybean Rotation

327

Fig. 1. Daily soil moisture, soil CO2–C emission rate, and season-long cumulative soil CO2–C emission in 2002 (soybean crop) as affected by the residual N fertilization rate from the previous corn crop at three sites. LSD values for CO2–C emission rate at a specific sampling date indicate significant differences between N rate (P ≤ 0.05); if no value is shown then the difference is nonsignificant. For the cumulative CO2–C emission, different letters indicate significant differences between N rate within each site (P ≤ 0.05).

the soybean year, even at the peak period of CO2–C emission. The lack of significant differences in CO2–C release during the growing season between all N treatments coincides with the lack of significant change in soil C fractions (data not presented). The effect of N rate greater than 0 kg N ha−1 on cumulative CO2–C emission was also inconsistent across sites, where the N rate of 180 kg N ha− 1 at the Boone site showed the lowest CO2–C emission compared to other N rates (Fig. 1). In contrast, no significant differences in cumulative CO2–C emission were observed at the Floyd or Warren sites (Fig. 1). It appears that the effect of N fertilization on soil CO2–C emission is inconsistent and it is highly site-specific, which can be attributed to differences in soil conditions. Two of the factors that may have an influence on CO2–C emission are soil moisture and soil temperature. However, simple regression correlation of CO2– C emission rates and soil moisture or temperature indicated that soil moisture or temperature was not well correlated with CO2–C emission (R2 = 0.11 and R2 = 0.32 at p = 0.05, respectively). These findings agree with those reported by Lou et al. (2004) and Buyanovsky and Wagner (1998), where they reported poor relationship between CO2–C emission and soil moisture content.

328

This poor relationship was attributed largely to soil moisture spatial variability and a shallow depth (0 to 5 cm) for soil moisture measurement, which is not deep enough to include the effect of root and microbial activities on CO2–C emission (Franzluebbers et al., 1994; Lou et al., 2004). The influence of N fertilization on soil microbial activity and CO2–C emission is not well understood and results reported by other investigators are inconsistent. For example, N fertilization had no influence on soil microbial biomass in corn–soybean systems (Willson et al., 2001). In contrast, it was reported that soil microbial activity may increase due to N fertilization as a result of increased plant biomass production, which on incorporation stimulates soil biological activity (Dick, 1992). However, the lack of a significant effect of N application in the prior corn crop on CO2–C emission during the soybean growing season coincided with the limited effect N fertilization had on soil C change over 3 yr in this study (data not presented).

Carbon Dioxide Emission from Soil during Corn Production The soil CO2–C emission rate during the corn phase of the corn–soybean rotation was significantly different between N rates


Fig. 2. Daily soil moisture, soil CO2–C emission rate, and season-long cumulative soil CO2–C emission in 2003 (corn crop) as affected by N fertilizer rate applied to the corn in 2003 at three sites. LSD values for CO2–C emission rate at a specific sampling date indicate significant differences between N rate (P ≤ 0.05); if no value is shown then the difference is nonsignificant. For the cumulative CO2–C emission, different letters indicate significant differences between N rate within each site (P ≤ 0.05).

at certain times, especially in the mid part of the growing season (Fig. 2), but had no effect at most measurement dates. Most often the greatest CO2–C emission rate was with zero N applied. The effect of N rate on CO2–C emission was inconsistent across the growing season. This inconsistency appeared to be related to soil moisture and temperature variability within the fields (Fig. 2). The overall trend of soil CO2–C emission rate was similar to that found during the soybean phase, where the maximum CO2– C emission was observed during the rapid vegetative growth stage (60 to 80 d after planting), which may indicate greater root respiration during such time in the growing season. The N rate effect on season-long cumulative CO2–C emission was site-specific. At the Boone site, the cumulative CO2–C emission was lowest with the 180 kg N ha−1 rate, similar to that measured in the soybean phase (Fig. 1 and 2). Other N rates had no effect on cumulative CO2–C emission at that site. As observed during the soybean year, the cumulative CO2–C emission with different N rates at the Floyd site showed no significant differences. Nitrogen application decreased cumulative CO2–C emission at the Tama site (Fig. 2). Increasing N fertilizer application rate was site specific and had inconsistent effect on depressing

CO2–C emission during the corn year (Fig. 2). These results in general are consistent with other findings of field and laboratory studies that indicate soil CO2 emission was depressed with N fertilization (Kowalenko et al., 1978). However, several studies concluded that change in soil C dynamics is a function of interrelated factors that include crop rotation, soil type, soil moisture, and soil temperature among many, which affect soil C loss (Rochette et al., 1999; Moore et al., 2000; Pietikäinen et al., 2005).

Soil Incubation and Microbial Biomass Carbon To eliminate the corn root system contribution to CO2–C production in the soil system and to evaluate the effect of N fertilization application on microbial biomass, a laboratory incubation study was conducted. Soil CO2–C emission during the laboratory incubation revealed more consistent and clear differences between N rates than the in situ soil CO2–C measurements (Fig. 3). The initial soil CO2–C emission rate 1 d after soil incubation was not significantly different for the soil collected from the four field study N rate treatments at any of the three sites (Fig. 3). The trend for soil CO2–C emission rate with all N rates for soil from each site had a similar rapid


329

Fig. 3. Soil CO2–C emission rate and cumulative CO2–C emission during laboratory incubation of soil samples (0–15-cm depth) collected from three 2003 corn sites in June at four N rates. LSD values for CO2–C emission rate at a specific sampling date indicate significant differences between N rate (P ≤ 0.05); if no value is shown then the difference is nonsignificant. For the cumulative CO2–C emission, different letters indicate significant differences between N rate within each site (P ≤ 0.05).

decrease in CO2–C emission rate within 7 d of beginning incubation. The greatest CO2–C emission rate, when significantly different between N rates, was with the zero N treatment. The cumulative soil CO2–C emission for the entire incubation period was greatest with zero applied N and decreased as N rate increased (Fig. 3). This occurred with soil from all three sites. These findings are surprisingly consistent with the field soil CO2– C emission measurements (Fig. 2), especially in the corn year. The decrease in soil CO2–C emission with higher N fertilization rates has been found by other investigators (Kowalenko et al., 1978; Ma et al., 1999), which is in agreement with our findings of N fertilization effect in decreasing CO2 emission. Soil CO2 flux in general can be an indictor of microbial activity during the oxidation of organic matter. However, the impact of N fertilization on such activities and CO2 release has been reported inconsistent, with decrease (Biederbeck et al., 1984; Ladd et al., 1994, Smolander et al., 1994) or increase (Entry et al., 1996; Conti et al., 1997). Other investigators found that N fertilization may decrease soil respiration due to a change in soil pH (de Jong et al., 1974; Smolander et al., 1994; Ladd et al., 1994). Nitrogen fertilization can decrease soil pH in the short-term and over time due to nitrification of ammonium. However, soil pH with the N rate treatments in our study was not changed significantly in the short period of this study

330

(data not presented). As observed with the N rate effect on CO2–C emission during this study, the differences in MBC concentrations between sites were inconsistent, and only one site (Floyd) showed significant difference in MBC concentrations between N fertilization rates (Fig. 4A). The greatest MBC concentration was associated with the 225 kg N ha−1 rate compared to other N rates at that site. It has been suggested that factors such as soil temperature, soil moisture, and soil fauna, among many others, can have a significant effect on the overall soil respiration in the field (de Jong et al., 1974; Dick, 1992). Nitrogen fertilization effects on soil microbial biomass were also evaluated by determining the potential mineral N supply through organic N mineralization in each soil (Fig. 4B). Except for the Tama site N application significantly increased net N mineralization. However, N rates greater than 90 kg N ha−1 did not increase net N mineralization in soil from the Boone or Tama site, but did in soil from the Floyd site. Some studies have noted no effect of N fertilization on the net N mineralization (Franzluebbers et al., 1994; Carpenter-Boggs et al., 2000), while others found decrease in net N mineralization (McAndrew and Malhi, 1992; Wienhold and Halvorson, 1999). Studies have also shown that symbiotic and asymbiotic N fixation decline with increasing soil inorganic N (Knowles and Denike, 1974; Stacey et al., 1992).


Fig. 4. (A) Microbial biomass C and (B) net mineralized soil N concentrations for soil samples (0–15-cm depth) collected from three 2003 corn sites in June at four N rates. Different letters indicate significant differences between N rates within each site (P ≤ 0.05).

Conclusions Across all sites and the two crops, soil CO2–C emission rates peaked during the most active crop growth period. The different N fertilization rates had no consistent significant effect on soil CO2–C emission rate regardless of site, although the zero N rate was greatest when significant. At some measurement dates, especially early- to mid-season, application of N significantly depressed emission rates. Season-long cumulative soil CO2–C emission in the soybean production year was not generally affected by N application in the prior corn crop. During the soybean year, although the trend in soil CO2–C emission rate over time was similar to that in the corn year, the cumulative CO2– C emission from all N treatments was not significantly different at two of three sites, and only decreased with application of 90 kg N ha−1 at one site. However, in the corn year N application at all rates decreased cumulative soil CO2–C emission. Soil in the third crop year had no change in MBC with N application at two sites, and only a significant increase at one site with the highest N rate. Soil CO2–C emission in the soil incubation experiment revealed more consistent differences between the N rate effect on CO2–C emission than with the field measurements. The greatest cumulative amount of soil CO2–C emission was with no applied N, and decreased significantly as N rate increased. This trend was consistent for soil collected from all sites. Also, the net N mineralization increased with increasing N rate applied to the corn crop. The results of the field and incubation study show no short-term effect of N fertilization within the sea-

son of N application during the corn production year, and in the following year for soybean on CO2–C release from soil. If there is any effect, it is both a reduced emission rate and reduced seasonlong cumulative emission of CO2–C with N application.

References Anderson, J.P.E. 1982. Soil respiration. p. 831–866. In A.L. Page (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. Agron. Monogr. 9, 2nd ed. ASA, Madison, WI. Bajracharya, R.M., R. Lal, and J.M. Kimble. 2000. Diurnal and seasonal CO2–C emission from soil as related to erosion phases in Central Ohio. Soil Sci. Soc. Am. J. 64:286–293. Biederbeck, V.O., C.A. Campbell, and R.P. Zentner. 1984. Effect of crop rotation and fertilization on some biological properties of a loam in southwestern Saskatchewan. Can. J. Soil Sci. 64:355–367. Buyanovsky, G.A., and G.H. Wagner. 1998. Carbon cycling in cultivated land and its global significance. Glob. Change Biol. 4:131–141. Carpenter-Boggs, L., J.L. Pikul, Jr., M.F. Vigil, and W.E. Riedell. 2000. Soil nitrogen mineralization influenced by crop rotation fertilization. Soil Sci. Soc. Am. J. 64:2038–2045. Conti, M.E., N.M. Arrigo, and H.J. Marrelli. 1997. Relationship of soil carbon light fraction, microbial activity, humic acid production and nitrogen fertilization in the decaying process of corn stubble. Biol. Fertil. Soils 25:75–78. de Jong, E., H.J.V. Schappert, and K.B. MacDonald. 1974. Carbon dioxide evolution from virgin and cultivated soil as affected by management practices and climate. Can. J. Soil Sci. 54:299–307. Dick, R.P. 1992. A review: Long-term effects of agricultural systems on soil biochemical and microbial parameters. Agric. Ecosyst. Environ. 40:25–36. Edwards, C.A., D.E. Reichle, and D.A. Crossley, Jr. 1970. The role of soil invertebrates in turnover of organic matter and nutrients. p. 12–172. In D.E. Reichle (ed.) Analysis of temperate forest ecosystems. SpringerVerlag, New York.


331

Entry, J.A., C.C. Mitchell, and C.B. Backman. 1996. Influence of management practices on soil organic matter, microbial biomass, and cotton yield in Alabama “Old Rotation.”. Biol. Fertil. Soils 23:353–358. Franzluebbers, A.J., F.M. Hons, and D.A. Zuberer. 1994. Tillage and crop effects on seasonal dynamics of soil CO2 evolution, water content, temperature, and bulk density. Appl. Soil Ecol. 2:95–109. Fritz, P., E.J. Reardon, J. Barker, R.M. Brown, J.A. Cherry, R.W.D. Killey, and D. McNaughton. 1978. The carbon isotope geochemistry of a small groundwater system in Northeastern Ontario. Water Resour. Res. 14:1059–1067. Hanson, P.J., N.T. Edwards, C.T. Garten, and J.A. Andrews. 2000. Separating root and soil microbial contributions to soil respiration: A review of methods and observations. Biogeochemistry 48:115–146. Horwath, W.R., and E.A. Paul. 1994. Microbial biomass. p. 753–773. In Methods of soil analyses: II. Microbiological and biochemical properties. SSSA Book Series 5. SSSA, Madison, WI. Knowles, R., and D. Denike. 1974. Effect of ammonium, nitrate, and nitrate-nitrogen on anaerobic nitrogenase activity in soil. Soil Biol. Biochem. 6:353–358. Kowalenko, C.G., K.C. Ivarson, and D.R. Cameron. 1978. Effect of moisture content, temperature, and nitrogen fertilization on carbon dioxide evolution from field soils. Soil Biol. Biochem. 10:417–423. Ladd, J.N., M. Amato, Z. Li-Kai, and J.E. Schultz. 1994. Differential effects of rotation, plant residue, and nitrogen fertilizer on microbial biomass and organic matter in an Australian alfisol. Soil Biol. Biochem. 26:821–831. Lou, Y., Z. Li, T. Zhang, and Y. Liang. 2004. CO2 emissions from subtropical arable soils of China. Soil Biol. Biochem. 36:1835–1842. Ma, B.L., L.M. Dwyer, and E.G. Gregorich. 1999. Soil nitrogen amendment effects on seasonal nitrogen mineralization and nitrogen cycling in maize production. Agron. J. 91:1003–1009. McAndrew, D.W., and S.S. Malhi. 1992. Long-term N fertilization of a solonetzic soil: Effects on chemical and biological properties. Soil Biol. Biochem. 24:619–623. Moore, J.M., S. Klose, and A.A. Tabatabai. 2000. Soil microbial biomass carbon and nitrogen as affected by cropping systems. Biol. Fertil. Soils 31:200–210. Mulvaney, R.L. 1996. Nitrogen-Inorganic forms. p. 1129–1131. In J.M. Bigham (ed.) Methods of soil analysis, Part 3. Chemical methods.

332

SSSA, Madison, WI. Paul, E.A., D. Harris, H.P. Collins, U. Schulthess, and G.P. Robertson. 1999. Evolution of CO2 and soil carbon dynamics in biologically managed, row-crop agroecosystems. Appl. Soil Ecol. 11:53–56. Pietikäinen, J., M. Pettersson, and E. Bååth. 2005. Comparison of temperature effects on soil respiration and bacterial and fungal growth rates. FEMS Microbiol. Ecol. 52:49–58. Ritchie, S.W., J.J. Hanway, and G.O. Benson. 1993. How a corn plant develops (ed.) J. Clayton Herman. Spec. Rep. no. 48. Iowa State Univ., Coop Ext. Service, Ames. Rochette, P., D.A. Angers, and L.B. Flanagan. 1999. Maize residue decomposition measurement using soil surgace carbon dioxide fluxes and natural abundance of carbon-13. Soil Sci. Soc. Am. J. 63:1385–1396. Rolston, D.E. 1986. Gas emission. p. 383–411. In A. Klute (ed.) Methods of soil analysis, Part 1. Physical and mineralogical methods. Agron. Monogr. 9. SSSA, Madison, WI. SAS Institute. 2003. The SAS system for windows. Release 9.1. SAS Inst. Inc., Cary, NC. Schlesinger, W.H. 1991. Biogeochemistry: An analysis of global change. Academic Press, San Diego, CA. Singh, J.S., and S.R. Gupta. 1977. Plant decomposition and soil respiration in terrestrial ecosystems. Bot. Rev. 43:449–528. Smolander, A., A. Kurka, V. Kitunen, and E. Malkonen. 1994. Microbial biomass C and N, and respiratory activity in soil of repeatedly limed and N- and P-fertilized Norway spruce stands. Soil Biol. Biochem. 26:957–962. Stacey, G., R.H. Burris, and H.J. Evans. 1992. Biological nitrogen fixation. Chapman and Hall, New York. Wienhold, B.J., and A.D. Halvorson. 1999. Nitrogen mineralization responses to cropping, tillage, and nitrogen rate in the northern Great Plains. Soil Sci. Soc. Am. J. 63:192–196. Willson, T.C., E.A. Paul, and R.R. Harwood. 2001. Biologically active soil organic matter fractions in sustainable cropping systems. Appl. Soil Ecol. 16:63–76. Witkamp, M., and M.L. Frank. 1969. Evolution of CO2 from litter, humus, and subsoil of a pine stand. Pedobiologia 9:358–365. Zibilske, L.M. 1994. Carbon mineralization. p. 836–864. In R.W. Weaver et al. (ed.) Methods of soil analysis, Part 2. Microbiological and biochemical properties. Agron. Monogr. 5. ASA and SSSA, Madison, WI.
