On-farm comparisons of soil organic carbon under no-tillage and chisel-plow systems

ABSTRACT

Purpose: Role of no-tillage (NT) in soil conservation has been already established but its influence on soil organic carbon (SOC) is still under debate.

Materials and methods: Three paired sites, with NT and chisel-plow (CT) fields adjacent to each other were selected for this study. Fields were under the same tillage practices for more than 20 years. Fields were sampled up to 90 cm depth to determine SOC and different C pools based on soil CO₂ flux during 86 d of incubation.

Results and conclusion: Significant differences in SOC and its pools were limited within the surface 0–15 cm depth only. Profile SOC did not vary between NT and CT. Tillage had a significant influence on soil C pools but the effect was not consistent across sites.

KEYWORDS:

• Northern great plains
• conservation tillage
• mineralization
• carbon pools
• C:N ratio
• bulk density

Introduction

Adopting no-tillage (NT) practices has long been recommended for increasing soil organic carbon (SOC) sequestration potential over conventional chisel plow or mouldboard tillage systems (CT) (Lal 2011). Physical disturbances associated with tillage increases microbial mineralisation of organic matter (Ogle et al. 2012). Kern and Johnson (1993) estimated that adoption of no-tillage (NT) across the United States would change the agricultural systems from C source (188–209 Tg C, 1 Tg = 10¹²g) to a C sink (131–306 Tg C). Smith et al. (2008) estimated that greenhouse gas mitigation potential of tillage and residue management practices was 0.17 and 0.53 t CO₂-equivalent ha⁻¹ yr⁻¹ in cool-dry and cool-moist climatic zones, respectively.

Recent studies raise significant doubts about the claim of no-tillage to potentially sequester SOC (Powlson et al. 2014). Many researchers (Blanco-Canqui and Lal 2008; Chatterjee and Lal 2009; Luo et al. 2010) found that NT had no effect on SOC in comparison to CT, when the whole soil profile (mineral horizon) was considered. Under NT practices, SOC in the 0–10 cm depth was increased by 3.15 ± 2.42 Mg ha⁻¹, but it was declined by 3.30 ± 1.61 Mg ha⁻¹ within the 20–40 cm layer (Luo et al. 2010). On the contrary, Olson et al. (2005) found that mouldboard systems had significantly less SOC in surface layers, subsurface (15–75 cm) and rooting zone (0–75 cm) than NT system at comparable depths after 12 years of corn-soybean rotation. It is evident that consideration of whole soil profile C is necessary to compare the effect of tillage on SOC (Blanco-Canqui and Lal 2008; Chatterjee and Lal 2009; Luo et al. 2010).

Further, success of NT on SOC accumulation depends on soil physical characteristics like texture (McConkey et al. 2003), and management practices, like fertiliser N input (Lemke et al. 2012) and crop rotation (Halvorson et al. 2016; Awale et al. 2013). McConkey et al. (2003) concluded that SOC sequestration is directly proportional to clay content under no-till in the Canadian Prairie regions. Further, cropping frequency and fertiliser N input in association with NT resulted in increased SOC (Lemke et al. 2012).

Adoption of NT is promoted for reductions of greenhouse gas emissions, diesel use, production costs and promotions of C sequestration and soil conservation (Lal 2011, Yang et al. 2013). In the Northern Great Plains of USA, Carr et al. (2015) revealed that NT had higher profile (depth of 90 cm) SOC (127 Mg C ha⁻¹) than reduced-tillage (104 Mg C ha⁻¹) and clean-tillage (112 Mg C ha⁻¹). Awale et al. (2013) found that NT had significantly higher SOC concentration by 3.8 and 2.7% and SOC stock by 7.2 and 9.2% in comparison to CT and strip tillage, respectively within 90 cm soil depth. This study was undertaken to determine differences in SOC of growers’ field under NT and CT practices. It was hypothesised that in spite of other differences in crop and soil management practices, NT had higher SOC than CT due to preservation of biochemical C fractions sensitive to disturbances. Long-term (∼20 yr) NT and CT paired fields were compared for profile SOC located at Sargent County of ND, USA.

Materials and methods

Three paired fields under long-term (>20 yrs) NT and CT practices, adjacent to each other, were selected within five-miles radius at Sargent County, ND, USA, during the fall of 2015. Detailed description of experimental fields is presented in Table 1. No-tillage practice was the same under three fields because these belongs to the same grower. No-tillage system involves only soil disturbance during planting. Planters incorporate some residue from the row through residue managers, finger coulters and double disk openers. Grain drills have a wavy coulter ahead of the seed tube to provide optimal seed placement. Chisel plow tills the soil to a depth of 15–20 cm using rows of staggered shanks. Primary tillage operation is conducted in the fall and is followed by the secondary tillage pass with a field cultivator in the spring before planting. Approximately 30 percent residue is left after spring tillage. Crop rotations were changed depending on market condition. Triplicate profile samples at 3 m interval along 9 m transect were collected from each field using a Giddings probe (Giddings Machine Company, Windsor, CO, USA) attached to a truck. Soil samples were separated into 0–15, 15–30, 30–60 and 60–90 cm depth increments. Total 72 soil samples (3 sites × 2 tillage treatments × 3 replications × 4 depths) were collected. Soil samples were thoroughly mixed in a bag and stored in a refrigerator (5°C) until it ready for analyses. Soil bulk density (ρ_b) was determined by the method as outlined by Blake and Hartge (1986). Briefly, soil sample from each depth was weighed after collection and sub-sample was dried at 105°C for 24 h to determine moisture content gravimetrically. Oven-dry soil weight of each depth was calculated using moisture content and divided by core volume (core internal diameter was 3.6 cm) to determine the soil BD of different depth increments.

Table 1. Site and soil information of three paired fields of no-tillage (NT) and chisel plow (CT) located at Sargent County, North Dakota.

Site	Coordinates	No-till for	Tile	Soil Series	Tillage	Crop rotation	Sand	Silt	Clay	Textural Class
								g kg^−1
1	45°58′10.4″N, 97°33′0.47″W	20 yr	Yes	Colvin-Borup Complex	CT	Corn-Soybean	274	451	275	Clay loam
					NT	Winter cereal-corn-soybean-flax/sunflower (4 yr. rotation)	407	394	200	Loam
2	45°59′54.6″ N 97°28′43.8″ W	36 yr	No	Aastad-Forman	CT	Corn-Soybean	278	447	275	Clay loam
					NT	Winter cereal-corn-soybean-flax/sunflower Last 4 yr. corn-soybean	242	446	313	Clay loam
3	45°59′11.4″N 97°26′35.5″ W	20 yr	Yes	Overly Bearden	CT	Corn-Soybean	382	369	250	Loam
					NT	Winter cereal-corn-soybean-flax/sunflower (4 yr. rotation)	292	433	275	Clay loam

Within one week after collection, fresh soil samples were used to analyze the inorganic concentrations. Briefly, 6.5 g field-moist soil sample was extracted with 2 M KCl and analyzed for concentrations using an automated Timberline 2800 Ammonia Analyzer (Timberline Instruments, Boulder, CO).

Field-moist soil samples were air-dried and sieved to pass through a 2-mm sieve. Processed soil samples of 0–15 cm were used to determine particle size distribution, pH, electrical conductivity (EC), soil available phosphorus (P), and potassium (K). Soil particle size distribution was determined by the hydrometer method as outlined by Elliott et al. (1999). For this, 40 g-soil sample was dispersed with 100 mL of sodium hexametaphosphate solution, and hydrometer was recorded at 4.5 and 8 h to compute clay and silt fraction and sand fraction, respectively, was determined gravimetrically after sieving the dispersed soil suspension through a 53 µm sieve. Soil pH and EC were measured electrometrically using an Oakton PC700 pH Bench Meter (Oakton Instr., IL, USA) in 1:2.5 soil:water extract (Thomas 1996). Soil available P and K were determined spectrophotometrically after extracting with 0.5 M sodium bicarbonate (NaHCO₃) (Olsen method) and 1 M ammonium acetate, respectively (NCR 1988).

A portion of air-dried soils was passed through a 0.5 mm sieve to obtain a homogeneous powder and analyzed for total C and N concentrations. Total C and N concentrations were determined by automated dry combustion (1050°C) method (Nelson and Sommers, 1996) using an Elementar Vario-Macro CN (Elementar Analysensysteme, GmbH, Germany). Inorganic C concentration was determined by combustion of pre-acidified (20% phosphoric acid) soil sample using Primacs^SLC TOC analyzer (Skalar Analytical, Buford, GA). Inorganic C percent was subtracted from total soil C to calculate SOC.

A laboratory incubation study was conducted to determine mineralisable C pools of surface soil layers (0–15 and 15–30 cm depths). Soil water filled pore space was determined by measuring the water content of saturated paste. Air-dried and sieved soil samples weighing 100 g were moistened to 50% of water filled pore space and incubated in a quart jars (0.946 L) for 86 days at 25°C. Cap of incubations jars were fitted with rubber septum and 25 mL headspace air was sampled using a syringe from each jar. Headspace air samples were collected on 1, 2, 3, 4, 7, 9, 11, 14, 17, 22, 30, 39, 42, 45, 65, 67, 71, 73, 78, and 86 days of incubation and analyzed for CO₂ concentration (ppm) using a DGA-42 Master Gas Chromatograph (Dani Instruments, Milan, Italy) fitted with TCD detector. CO₂ flux (µg CO₂–C g soil⁻¹ day⁻¹) for each sample was calculated using the following formula (Mukome et al. 2013):where f is the CO₂-C gas flux (µg g⁻¹soil day⁻¹); Ct is the gas concentration in the gas phase at time t (µL L⁻¹); Vh is the headspace gas volume (mL); M is the atomic weight of C (12.01 g mol⁻¹); P is the standard atmospheric pressure (101700Pa); R is the universal gas constant (8.3144 L kPa mol⁻¹ K⁻¹); T is the temperature in Kelvin (298 K); W is the oven-dry mass of soil (g); t is the time between the consecutive sampling days (day); and 1000 is the unit conversion factor (ml to L). Cumulative mg CO₂-C emission per g⁻¹ soil during the incubation period was calculated by summing the gas emissions (mg CO₂-C g⁻¹ soil) during each sampling period. The magnitude of different C pools, active, slow and resistant, and mineralisation rates were determined using a three pool constrained model described by Paul et al. (2001):

Where c_a = active soil C pool (µg C g⁻¹ SOC), C_r = resistant soil C pool(µg C g⁻¹ SOC), k_a = active soil C pool turnover rate (day⁻¹), C_s = slow soil C pool (C_SOC-C_a-C_r), k_s = slow soil C pool turnover rate (day⁻¹), k_r = resistant soil C pool turnover rate(day⁻¹), and t = time in days. Pool sizes and turnover rates of the active (C_a) and the slow (C_s) pools were estimated using curve analyses of the flux data. Non-hydrolysable SOC (resistant fraction of soil C or C_r) was measured by refluxing 1 g soil with 6 M HCl at 115°C for 16 h using a temperature controlled digestion block and analyzing soil C left after digestion. The non-hydrolysable SOC was analyzed using Primacs^SLC TOC analyzer (Paul et al. 2006). The mean residence time (MRT) of C_r was considered to be 500 years according to Paul et al. (2006) and hence the resistant soil C pool (k_r) turnover rate was 5.5 × 10⁻⁶ day⁻¹. Turnover rates of C_a (days) and C_s (years) were calculated by the reciprocals of K_a and K_s.

Soil organic C pool sizes (C_a, C_s and C_r) and turnover rates (k_a and k_s) were determined by the three-pool constrained nonlinear regression model using SAS PROC NLIN (ver. 9.4, SAS 2013) separately for each jar. The Cs pool was calculated by subtracting C_r and C_a pools from C_soc. One-way ANOVA was conducted for each site using randomised complete block design with three replications. Treatment means were separated using Fisher’s LSD test at the 95% significance level. Statistical analysis was performed using PROC ANOVA (SAS 9.4, 2013).

Results and discussion

Comparisons of three adjacent NT and CT paired fields revealed that tillage operation had significant effect on soil pH at site 3 and soil EC at site 1 and 2 (Table 2). Across all three sites, NT had lower soil pH than CT. Other researchers attributed the decrease in surface soil pH under NT to nitrification of surface applied N fertiliser (Blevins et al. 1983; Dick 1983). For soil EC, NT reduced surface soil EC for site 1 and 2. Dalal (1989) also found a significant decline soil EC due to increased and deeper water movement in soil under no-tillage compared with under CT. Tillage had no influence on soil available N, P and K within 0–15 cm depth. Soil samples were collected after harvest and residual nutrients were similar for all three sites.

Table 2. Mean (standard deviation) of basic soil chemical characteristics and nutrient availability within 0–15 cm depth of soils from no-tillage (NT) and Chisel plow (CT) of three paired field sites located at Sargent County, ND.

Site	Treatments	pH(1:2.5)		EC		Inorganic N		Olsen-P		K
		(soil:water)		dSm^−1		kg ha^−1		µg g^−1
1	CT	7.83	0.06^A*	0.77	0.03^A	28.4	18.1^A	10.3	1.53^A	267	55.9^A
	NT	7.57	0.06^A	0.39	0.08^B	23.0	7.45^A	11.3	2.52^A	232	34.6^A
	LSD (P = 0.05)	0.29		0.27		31.9		8.96		138
2	CT	7.77	0.06^A	0.79	0.05^A	17.07	11.3^A	41.3	13.5^A	343	36.0^A
	NT	6.63	0.78^A	0.34	0.11^B	14.14	2.66^A	45.7	21.9^A	375	33.0^A
	LSD (P = 0.05)	2.07		0.25		17.4		63.4		101
3	CT	8.00	0.01^A	0.46	0.09^A	16.04	4.56^A	29.3	7.64^A	269	35.9^A
	NT	7.53	0.15^B	0.54	0.18^A	13.30	4.02^A	33.0	14.9^A	313	43.1^A
	LSD (P = 0.05)	0.38		0.69		12.4		54.5		77.0

*Different capital letters indicated significant mean difference for the same site at P < 0.05. Inorganic nitrogen (N) = concentrations of , Olsen-P = available phosphorus analyzed b Olsen method, K = potassium.

Tillage had only an effect on soil BD and SOC within 0–15 cm depth for sites 1 and 2 (Table 3). Only at site 1, NT had higher BD than CT throughout the soil profile but the difference was significant only within 0–15 cm. Sand content of the NT field was almost twice that of CT. For other two sites, soil BD did not vary between two tillage systems for all depth increments. These findings did not support the common observations of increases in soil BD under continuous tillage systems (Lampurlanes and Cantero-Martinez 2003). It is common to find no differences in BD in between CT and NT. Blevins et al. (1983) did not find any difference in BD between CT and NT after 10 years. They hypothesised that freezing and thawing during the winter months probably recuperated the small amount of compaction occurring in the wheel track of the planter in a NT system. Moreover, Unger (1996) found that adverse soil physical conditions like, increased BD and penetration resistance, were limited to designated traffic zones only under NT system.

Table 3. Mean with standard deviation of soil bulk density (BD) (Mg m⁻³), SOC (Mg ha⁻¹), carbon to nitrogen ratio (C:N) and total nitrogen (N) content (Mg ha⁻¹) within 0–90 cm soil depth for three no-tillage (NT) and Chisel plow (CT) paired fields located at Sargent County, North Dakota.

Soil Depth (cm)	Site	Treatments	BD (Mg m^−3)		SOC (g kg^−1)		SOC (Mg ha^−1)		Total N (Mg ha^−1)		C:N
0–15	1	CT	1.02	0.16^B*	27.2	5.81^A	41.70	12.8^A	3.65	1.24^A	11.61	1.34^A
		NT	1.30	0.10^A	24.5	8.14^A	47.48	14.6^A	4.05	2.13^A	10.44	0.50^A
		LSD (P = 0.05)	0.12		12.9		27.3		3.24		2.83
	2	CT	1.13	0.16^A	27.0	1.16^B	45.58	6.50^B	4.35	0.58^A	10.47	0.33^B
		NT	1.12	0.06^A	32.9	1.25^A	55.11	2.12^A	4.77	0.23^A	11.57	0.36^A
		LSD (P = 0.05)	0.24		1.66		7.66		0.56		0.45
	3	CT	1.16	0.05^A	33.4	2.60^A	58.04	4.36^A	5.26	0.31^A	11.04	0.68^A
		NT	1.17	0.12^A	33.2	1.74^A	58.29	5.54^A	5.23	0.52^A	11.16	0.22^A
		LSD (P = 0.05)	0.19		4.20		2.42		0.79		1.37
15–30	1	CT	1.05	0.09^A	20.9	10.4^A	32.74	16.9^A	2.87	1.58^A	11.86	1.28^A
		NT	1.22	0.12^A	22.2	10.8^A	39.76	19.1^A	3.68	1.74^A	11.00	1.92^A
		LSD (P = 0.05)	0.22		26.9		42.0		3.66		3.11
	2	CT	1.23	0.10^A	18.0	2.65^A	33.37	5.80^A	2.94	0.63^A	11.48	0.93^A
		NT	1.19	0.06^A	19.1	1.80^A	34.06	1.44^A	3.21	0.16^A	10.62	0.18^A
		LSD (P = 0.05)	0.21		6.78		10.4		1.12		1.67
	3	CT	1.27	0.06^A	17.9	1.76^A	33.93	2.41^A	3.18	0.38^A	10.77	1.38^A
		NT	1.16	0.19^A	16.2	3.40^A	27.90	6.51^A	2.50	0.57^A	11.14	0.36^A
		LSD (P = 0.05)	0.29		7.59		14.0		1.29		1.96
30–60	1	CT	1.11	0.16^A	11.0	6.10^A	34.61	13.8^A	3.11	1.01^A	10.98	1.32^A
		NT	1.27	0.09^A	11.7	4.96^A	43.94	17.2^A	4.79	1.45^A	9.13	1.68^A
		LSD (P = 0.05)	0.29		12.8		31.2		2.65		2.54
	2	CT	1.32	0.10^A	16.6	11.9^A	64.64	42.8^A	3.25	0.37^A	11.11	2.18^A
		NT	1.31	0.11^A	11.1	1.39^A	43.42	4.40^A	3.92	0.31^A	11.10	0.90^A
		LSD (P = 0.05)	0.30		19.5		70.6		0.89		4.52
	3	CT	1.27	0.09^A	9.93	1.16^A	37.98	4.95^A	3.75	0.69^A	10.27	1.41^A
		NT	1.17	0.06^A	12.1	1.16^A	42.15	2.10^A	3.77	0.23^A	11.22	0.59^A
		LSD (P = 0.05)	0.19		3.07		10.2		1.23		2.36
60–90	1	CT	1.14	0.08^A	6.05	3.85^A	20.42	12.2^A	2.89	0.55^A	8.76	4.31^A
		NT	1.20	0.08^A	5.35	2.54^A	19.33	9.35^A	2.85	1.03^A	7.01	3.27^A
		LSD (P = 0.05)	0.20		7.47		23.9		2.66		2.66
	2	CT	1.36	0.16^A	5.33	1.51^A	21.36	4.28^A	NA
		NT	1.30	0.04^A	6.98	1.47^A	27.31	6.42^A	NA
		LSD (P = 0.05)	0.22		2.70		8.60
	3	CT	1.04	0.16^A	9.61	4.55^A	28.97	12.6^A	2.70	0.30^A	10.66	4.46^A
		NT	1.14	0.08^A	8.78	3.29^A	29.36	8.91^A	2.61	0.58^A	11.15	1.23^A
		LSD (P = 0.05)	0.30		4.39		8.96		1.01		6.24

NA = Below the detection limit.

*Different capital letters indicated significant mean difference between CT and NT for the same soil depth and site at P < 0.05.

Significant increase in terms of SOC concentration and SOC content with NT was observed at site 2, only within 0–15 cm depth (Table 4). Higher soil C:N ratio of NT than CT was also observed at the same site and depth increment. However, profile SOC (0–90 cm) did not show any significant difference between NT and CT for all three sites (Table 3). Lack of significant differences in SOC was also observed by Blanco-Canqui and Lal (2008) in 8 out of 11 Major Land Resource Areas with similar cropping systems suggesting that NT farming is equivalent to CT systems for storing SOC in the whole profile. Total soil N did not change with tillage for all depth increments and sites (Table 4). West and Post (2002) concluded that C sequestration rates with a change from CT to NT, can be expected to peak in 5–10 yr with SOC reaching a new equilibrium in 15–20 yr, from 276 paired treatments.

Table 4. Mean with standard deviation of profile soil organic carbon (SOC) (Mg ha⁻¹) of 90 cm depth under no-tillage (NT) and chisel plow (CT) practices of three paired field sites.

Site	Tillage	Profile SOC (Mg ha^−1)
1	CT	129.5	52.3
	NT	150.5	50.5
	LSD (P = 0.05)	115
2	CT	164.9	55.6
	NT	159.9	6.04
	LSD (P = 0.05)	88.0
3	CT	158.9	10.9
	NT	157.7	16.4
	LSD (P = 0.05)	15.9

Incubation study results showed that most significant differences in SOC pools and their relative contributions to SOC and their MRTs were restricted only within the 0–15 cm depth of site 2 and site 3 (Table 5). Soils from NT field had higher cumulative flux than CT for all three sites and depth increments; but the difference was not significant at 95% significance level (Table 5). Johnson et al. (2010) found an ephemeral CO₂ response to chisel and mouldboard tillage with a minimal impact of tillage on annual soil CO₂ flux in silty clay loam soils.

Table 5. Mean of soil carbon (C) pools, cumulative, active (C_a), slow (C_s), and resistant (C_r), their relative percent contributions to SOC, and mean residence time (MRT) of Ca (days) and Cs (years) within 0–15 and 15–30 cm soil depths in response to no-tillage (NT) and Chisel plow (CT) for three paired field sites located at Sargent County, North Dakota.

Soil Depth (cm)	Site	Treatments	Cumulative	Ca	%Ca	Ca-MRT	Cs	%Cs	Cs-MRT	Cr	%Cr
			µg g^−1	mg g^−1		days	mg g^−1		Years	mg g^−1
0–15	1	CT	224	0.11	0.40	4.41	17.1	59.6	33.9	12.0	40.0
		NT	323	0.19	0.68	3.23	19.2	70.8	25.0	8.27	28.5
	LSD (P = 0.05)		594	0.23	0.51	10.8	4.09	41.8	99.0	17.8	41.8
	2	CT	247	0.13	0.48	5.52	15.7	59.7	25.7^A	10.5^B	39.8
		NT	309	0.11	0.35	1.53	17.1	52.6	15.3^B	15.2^A	47.0
	LSD (P = 0.05)		261	0.26	0.92	6.47	2.66	10.2	9.67	3.78	9.84
	3	CT	185	0.15^A	0.44^A	8.63^A	18.8	54.6	99.0^A	15.4	44.9
		NT	167	0.08^B	0.25^B	3.44^B	15.3	46.4	32.5^B	17.6	53.4
	LSD (P = 0.05)		22.8	0.03	0.07	3.20	6.63	15.4	31.3	3.98	15.4
15–30	1	CT	122	0.07	0.29	8.98	14.2	54.7	67.7	11.3	45.0
		NT	133	0.08	0.42	6.31	15.7	74.3	78.3	6.58	25.3
	LSD (P = 0.05)		50.2	0.10	0.42	14.2	28.9	31.6	270	17.5	31.9
	2	CT	109	0.06	0.34	7.80	12.0	65.8	59.9	6.43	33.9
		NT	157	0.13	0.68	9.35	9.49	51.6	65.5	8.76	47.7
	LSD (P = 0.05)		105	0.24	1.27	2.90	6.90	32.0	136	8.51	30.8
	3	CT	108	0.05	0.29	7.39	11.3	63.1	46.2	6.51	36.6
		NT	121	0.05	0.38	8.06	9.92	66.6	34.3	5.32	33.0
	LSD (P = 0.05)		51.2	0.06	0.54	8.96	5.64	18.0	30.6	7.94	18.5

Significant increases in C_a pool, percent contribution of C_a to SOC and MRT of C_a with CT than NT were observed at site 3. Higher MRT of Cs pool of CT soil than NT was observed at site 2 and site 3. However, NT soil had higher Cr than CT at site 2. It is generally hypothesised that tillage operations lead to loss of C through decomposition and shifts in distributions of active, slow and resistant C pools (Paul et al. 2006). Ogle et al. (2012) reported that the distribution and spatial pattern of steady state SOC is the results of C input rates, which are driven by crop productivity and MRT of SOC which is controlled mainly by climate and soil texture. They also concluded that the absolute largest differences in MRTs of SOC between CT and NT system occurred in cool and dry soils with low decomposition rate and high clay + silt content.

It is a challenge to eliminate all unwanted sources of SOC variation (texture and landuse history) in comparing on-farm tillage studies (Luo et al. 2010, Costa Junior et al. 2013). However, growers are interested to compare NT and CT considering all other differences in soil and crop management practices. Our study showed adoption of NT might not always increase SOC than CT, or the differences in soil variability and crop rotation might mask the small differences in SOC between two systems.

Disclosure statement

No potential conflict of interest was reported by the author.

Notes on contributor

Dr. Amitava Chatterjee received his doctoral degree in soil science from University of Wyoming in 2007. His research program examines the control of climate plant soil interaction on soil nutrient availability, nutrient losses and crop response. He has published 40 peer-reviewed manuscripts and co-edited a book (Soil Fertility in Agroecosystems). He teaches undergraduate and graduate courses in soil fertility. He has advised seven master's and four doctoral students. He serves as an associate editor of Agronomy Journal.