Tillage, Cropping Sequence, and Nitrogen ... - PubAg - USDA

Agronomy, Soils & Environmental Quality

Tillage, Cropping Sequence, and Nitrogen Fertilization Influence Dryland Soil Nitrogen Upendra M. Sainju* ABSTRACT

Management practices can reduce N losses through N leaching and N2O emissions (a greenhouse gas) by increasing soil N storage. The effects of tillage, cropping sequence, and N fertilization rate were studied on N contents in dryland crop biomass, surface residue, and soil at the 0- to 120-cm depth, and estimated N balance from 2006 to 2011 in eastern Montana. Treatments were no-till continuous malt barley (Hordeum vulgaris L.) (NTCB), no-till malt barley–pea (Pisum sativum L.) (NTB–P), no-till malt barley–fallow (NTB–F), and conventional till malt barley–fallow (CTB–F), each with 0 to 120 kg N ha–1. Biomass and surface residue N increased with increased N rate and were greater in NTB–P or NTCB than CTB–F and NTB–F in all years, except in 2006 and 2011. Soil total nitrogen (STN) at 0 to 60 cm decreased from 2006 to 2011 at 254 kg N ha–1 yr–1, regardless of treatments. At most depths, soil NH4 –N content varied, but NO3 –N content was greater in CTB–F than other cropping sequences. Estimated N balance was greater in NTB–P with 40 kg N ha–1 than other treatments. No-till continuous cropping increased biomass and surface residue N, but conventional till crop–fallow increased soil available N. Because of increased soil N storage and reduced N requirement to malt barley, NTB–P with 40 kg N ha–1 may reduce N loss due to leaching, volatilization, and denitrification compared to other treatments.

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major nutrient required in ample amount to sustain crop yield and quality is N. Nitrogen fertilization can increase crop yields, but excessive application can degrade soil and environmental quality by increasing soil acidification, N leaching, and emissions of N2O, a highly potent greenhouse gas with shared responsibility for global warming (Franzluebbers, 2007; Herrero et al., 2010). An increase in soil N storage can reduce N losses through leaching, volatilization, denitrification, surface runoff, erosion, and N2O emissions (Sainju et al., 2012). Since N mineralized from crop residue and soil is also added to the available N pool, information on N storage and mineralization is needed to optimize N availability for crop growth, increase N-use efficiency, sustain crop yield and quality, and reduce N fertilization rate and the potential for N loss. Challenges remain to increase N storage in soil and surface residue under semiarid dryland cropping systems in the northern Great Plains because of lower crop residue N returned to the soil due to limited precipitation and shorter growing season than in humid regions (Campbell et al., 1989; Sainju et al., 2009). The traditional farming system using conventional tillage with crop–fallow can conserve soil water during fallow, increase N availability due to increased N mineralization, control weeds, sustain crop yields, and reduce the risk of crop USDA-ARS, Northern Plains Agricultural Research Laboratory, Sidney, MT 59270. Mentioning the name of a product is for the use of consumers only and does not necessarily contribute to an endorsement by USDAARS. USDA-ARS is an equal opportunity employer. Received 2 Mar. 2013. *Corresponding author ([email protected]). Published in Agron. J. 105:1253–1263 (2013) doi:10.2134/agronj2013.0106 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. 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.

failure (Aase and Pikul, 1995; Jones and Popham, 1997). The system, however, can reduce soil N storage because of increased erosion and mineralization of organic N and reduced plant residue N returned to the soil due to the absence of crops during fallow (Bowman et al., 1999; Halvorson et al., 2002). Enhanced microbial activity due to increased soil temperature and water content during fallow can further reduce N storage (Haas et al., 1974; Halvorson et al., 2002). Studies have shown that conventional tillage with crop–fallow has reduced soil N storage by 30 to 50% in the last 50 to 100 yr (Haas et al., 1974; Peterson et al., 1998) and reduced annualized crop yields (Aase and Pikul, 1995; Sainju et al., 2013). As a result, the system became unsustainable and uneconomical (Aase and Schaefer, 1996; Dhuyvetter et al., 1996). Improved soil and crop management practices, such as reduced tillage and continuous cropping, can increase dryland N storage to a depth of 20 cm compared to a traditional farming system (Sherrod et al., 2003; Sainju et al., 2006). Besides reducing N mineralization, no-till can conserve surface residue and soil water more than conventional till (Farahani et al., 1998). As a result, crops can use soil water more efficiently in no-till (Deibert et al., 1986; Aase and Pikul, 1995), which can reduce or eliminate summer fallow by increasing cropping intensity (Farahani et al., 1998; Peterson et al., 1998). Similarly, crops grown in rotations or with shorter fallow periods often have higher annualized biomass N than monocrop systems or with longer fallow periods (Copeland and Crookston, 1992; Halvorson et al., 2002). Including pea in rotation with spring wheat (Triticum aestivum L.) and barley can not only sustain their yields by efficiently using soil water but also reduce N

Abbreviations: CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; NTCB, no-till continuous malt barley; STN, soil total nitrogen.

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fertilization rates by supplying supplemental N from the pea residue due to its higher N concentration (Miller et al., 2002; Sainju et al., 2009, 2013; Sainju and Lenssen, 2011). The increase water-use efficiency is a result of less soil water use by pea than spring wheat and barley, thereby leaving more water available for succeeding crops and increasing their yields (Miller et al., 2002; Lenssen et al., 2007). Other benefits of crop rotation compared to monocropping include control of weeds, diseases, and pests (Vigil et al., 1997; Miller et al., 2002), reduction in farm inputs, and improvement in economic and environmental sustainability (Gregory et al., 2002). Nitrogen fertilization rates can be higher for the no-till than for the conventional till cropping system due to greater accumulation of surface crop residue that can enhance N immobilization (Zibilske et al., 2002). On the other hand, N rates can be reduced in crop rotations containing legumes compared to monoculture nonlegume cropping systems (Heichel and Barnes, 1984). Increased cropping intensity can reduce soil profile NO3–N content due to greater N immobilization, less summer fallow, and greater amount of N removed by crops (Wood et al., 1990). Increasing the fallow period can increase N loss below the root zone due to leaching and absence of crops to use N (Eck and Jones, 1992). Although N is removed during the harvest of crop grains, N in aboveground biomass (stems + leaves) is either harvested or returned to the soil. Nitrogen in belowground biomass (root) is recycled back to the soil. While most N is stored as soil organic N and some in the surface residue, some N can be lost through leaching, volatilization, denitrification, surface runoff, erosion, and N2O emissions. These N loss mechanisms can increase with increased tillage frequency and greater with crop–fallow than with continuous cropping systems (Sainju et al., 2009). Accounting of N sources and sinks and removal by crops can provide an estimate of N balance that would be helpful to optimize N availability for crop growth, increase N-use efficiency, and reduce N fertilization rate and the potential for N losses (Sainju et al., 2009, 2012). Information on N dynamics in crops and soil as affected by management practices under dryland malt barley cropping systems in the northern Great Plains is limited. It was hypothesized that NTB–P with 40 kg N ha–1 would increase surface residue and soil N storage, optimize N availability, and reduce the potential for soil N losses compared to CTB –F with 80 to 120 kg N ha–1. The objectives of the experiment were to: (i) evaluate the effects of tillage, cropping sequence, and N fertilization on dryland crop biomass (stems and leaves) N returned to the soil, surface residue N, and soil total N (STN), NH4 –N, and NO3–N contents at the 0- to 120-cm depth from 2006 to 2011 in eastern Montana, (ii) estimate N balance in various management practices after accounting for all sources and sinks of N, and (iii) identify management practices that increase N storage or reduce N loss. MATERIALS AND METHODS Field Methods The details of the field experiment regarding site and treatment descriptions and crop management have been described by Sainju et al. (2013). Briefly, the experiment was conducted from 2006 to 2011 at a dryland farm site in Sidney, MT, in a 1254

Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustolls), with 350 g kg–1 sand, 325 g kg–1 silt, 325 g kg–1 clay, 7.2 pH at the 0- to 30-cm depth and STN concentrations of 1.37, 1.17, and 0.93 g N kg–1 at 0 to 5, 5 to 10, and 10 to 30 cm, respectively, in April 2006. Treatments included four tillage and cropping sequence combinations (no-till continuous malt barley [NTCB], no-till malt barley–pea [NTB–P], notill malt barley–fallow [NTB–F], and conventional till malt barley–fallow [CTB–F]) (hereafter called cropping sequences) as the main plot and four N fertilization rates (0, 40, 80, and 120 kg N ha–1) as the split plot factor arranged in a randomized complete block with three replications. Each phase of the cropping sequence occurred every year. The CTB–F with 80 kg N ha–1 is the traditional dryland farming practice for malt barley in the region. Nitrogen rates were adjusted to soil NO3–N content to a depth of 60 cm after crop harvest in the fall of the previous year so that desired N rates contained both soil and fertilizer N. Malt barley and pea were planted in April and harvested in August. After grain harvest, malt barley and pea biomass residues were returned to the soil. In October 2006 to 2011, 2 mo after grain harvest, soil surface residue samples were collected from five 30 by 30 cm areas from central rows per plot, composited, washed with water to remove soil, and oven dried at 60°C for 7 d to obtain dry matter weight. Samples were ground to pass a 1 mm screen before N analysis. After removing the residue, soil samples were collected with a hydraulic probe (5 cm i.d.) attached to a truck from the 0- to 120-cm depth from five places in central rows per plot. Soil cores were separated into six segments to represent six depths (0 to 5, 5 to 10, 10 to 30, 30 to 60, 60 to 90, and 90 to 120 cm), composited within a depth, air-dried, ground, and sieved to 2 mm for determining N concentration. A subsample (~10 g) of each soil core was oven dried at 110°C for 24 h for bulk density determination, which was calculated as the weight of the oven-dried soil divided by the volume of the core. Laboratory Analysis Total N concentration (g N kg–1) in crop grain and biomass and soil surface residue was determined by using a high combustion C and N analyzer (LECO Corp., St Joseph, MI). Nitrogen content (kg N ha–1) in grain, biomass, and surface residue was determined by multiplying dry matter weight by N concentration. The STN concentration (g N kg–1) in soil samples was determined by using the C and N analyzer as above after grinding the samples to NTCB > NTB–F = CTB–F. Greater annualized crop biomass N in continuous cropping than crop–fallow in dryland cropping systems from 2007 to 2009 was probably due to higher annualized yield, although the crop–fallow system produces higher biomass N during the crop year (Sainju et al., 2006, 2009). In contrast, greater biomass N in NTB–P than in NTCB in 2010 and 2011 was likely due to higher tissue N concentration in pea than in malt barley and/or lower N concentration in malt barley as a result of N dilution from increased biomass yield during

Fig. 1. Effects of (A) cropping sequence (B) N fertilization rate on annualized crop biomass (stems + leaves) N returned to the soil from 2006 to 2011. CTB–F denotes conventional till malt barley-fallow; NTB–F, no-till malt barley–fallow; NTB–P, notill malt barley–pea; and NTCB, no-till continuous malt barley. Bars followed by different letters at the top are not significantly different at P £ 0.05 by the least significant difference test.

wet years. Crop growing season precipitation (April–August) were 349 mm in 2010 and 292 mm in 2011 compared to 244, 226, 126, 211, and 242 mm in 2006, 2007, 2008, 2009, and the 68-yr average, respectively. Sainju et al. (2009, 2012) also observed greater annualized crop biomass N content in spring wheat–pea rotation than in continuous spring wheat during years with above-average precipitation. Nonsignificant difference in biomass N between CTB–F and NTB–F suggests that tillage had no influence on crop biomass N. Similar results have been reported by various researchers for dryland cropping systems in the northern Great Plains (Halvorson et al., 2002; Sainju et al., 2009, 2012). Biomass N, averaged across cropping sequences and years, was greater with 80 and 120 than with 0 and 40 kg N ha–1 (Fig. 1). It is not unusual to observe higher crop biomass N with increased N fertilization rates due to increased soil N availability (Halvorson and Reule, 2007; Abeledo et al., 2008). Similar biomass N levels between 80 and 120 kg N ha–1 suggests that the application of 120 kg N ha–1 to dryland malt barley in the northern Great Plains is excessive and should be discouraged to reduce the cost of N fertilization and improve environmental quality by reducing N leaching and N2O emissions. Soil Surface Residue Nitrogen As with crop biomass N, soil surface residue N varied with cropping sequences, N fertilization rates, and years, with significant cropping sequence × year interaction (Table 1). In 2007, surface residue N was greater in NTB–P and NTCB than in CTB–F (Table 2). In 2008, surface residue N was greater in NTCB than in CTB–F and NTB–P and greater in NTB–F than in CTB–F. In 2009, surface residue N was greater in

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Table 1. Effects of cropping sequence and N fertilization rate on soil surface residue N content from 2006 to 2011. Treatment/year Cropping sequence† CTB–F NTB–F NTB–P NTCB N fertilization rate, kg N ha–1 0 40 80 120 Year 2006 2007 2008 2009 2010 2011 Significance Cropping sequence (C) N fertilization rate (N) C×N Year (Y) C ×Y N ×Y C × N ×Y

Surface residue N content kg N ha–1 14.9b‡ 16.4b 16.8b 20.5a 13.7c 16.2b 17.8b 20.9a 9.5c 19.8ab 16.9b 20.3a 18.6ab 17.9ab ** *** ns§ *** *** ns ns

** Significant at P £ 0.01. *** Significant at P £ 0.001. † Cropping sequences are CTB-F, conventional till malt barley-fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; and NTCB, no-till continuous malt barley. ‡ Numbers followed by different letters within a column in a set are significantly different at P £ 0.05 by the least significant difference test. § ns, not significant.

NTB–P than in CTB–F and NTB–F and greater in NTCB than in CTB–F. In 2010, surface residue N was greater in NTCB and CTB–F than in other cropping sequences. Greater surface residue N in NTB–P and NTCB than in CTB–F in 2007 and 2009 was probably due to higher amount of annualized crop biomass N returned to the soil (Fig. 1) and limited soil disturbance. Soils were not disturbed in NTB–P and NTCB, except during fertilization and planting crops in rows, as opposed to disturbance due to tillage to prepare seed bed and control weeds in CTB–F. As a result, most of the crop biomass N accumulated at the soil surface with limited contact with soil microorganisms due to reduced tillage, thereby increasing surface residue N in NTB–P and NTCB compared to CTB–F. In CTB–F, tillage may have incorporated residue to a greater depth into the soil, resulting in lower surface residue N. Similar increases in soil surface residue N in no-till continuous cropping compared to conventional till crop–fallow have been previously reported (Sainju et al., 2009, 2012). Similarly, greater surface residue N in NTB–F than in CTB–F in 2008 was probably due to placement of biomass residue at the soil surface due to reduced tillage. Greater surface residue N in NTCB than in NTB–P in 2008 and 2010 was probably related to residue quality, since pea residue with lower C/N 1256

Table 2. Interaction of cropping sequence with year on soil surface residual N content averaged across N fertilization rates. Cropping sequence† CTB–F NTB–F NTB–P NTCB

Surface residue N content 2006 2007 2008 2009 2010 2011 ———————————— kg N ha–1 ———————————— 9.0a‡ 15.5b 12.3c 13.5c 23.0a 16.3a 9.9a 18.3ab 18.6ab 19.1bc 13.1b 19.5a 9.1a 22.2a 14.7bc 25.2a 12.4b 17.3a 10.2a 23.0a 22.1a 23.2ab 25.9a 18.8a

† Cropping sequences are CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; and NTCB, no-till continuous malt barley. ‡ Numbers followed by different letters within a column are significantly different at P £ 0.05 by the least significant difference test.

ratio decomposes more rapidly than malt barley residue with higher ratio (Sainju et al., 2009, 2012). In contrast, higher crop biomass N returned to the soil (Fig. 1) probably increased surface residue N in CTB–F than in NTB–F in 2010. Averaged across N rates and years, surface residue N was greater in NTCB than in other cropping sequences (Table 1). Higher amount of crop biomass N returned to the soil, followed by slower decomposition of malt barley than pea residue due to higher C/N ratio, probably increased surface residue N in NTCB compared to other cropping sequences. Like crop biomass N, nonsignificant difference between CTB–F and NTB–F suggests that tillage, overall, did not influence surface residue N. Similar result has been observed by Sainju et al. (2006, 2012) who reported that harsh environmental conditions and cold weather limited the effect of tillage on soil surface residue N in the northern Great Plains. Averaged across cropping sequences and years, surface residue N was greater with 120 kg N ha–1 than with other N rates and greater with 40 and 80 than with 0 kg N ha–1. Increases in surface residue N with increased N rates were proportional to higher crop biomass N returned to the soil (Fig. 1). Averaged across treatments, surface residue N was greater in 2009 than in 2006 and 2008. Presence of large proportion of undecomposed residue from 2008 due to lower precipitation probably increased surface residue N in 2009. Total annual precipitation in 2008 was 189 mm compared to 282 mm in 2009. The reasons for lower surface residue N in 2006 were not known. Soil Total Nitrogen The STN varied with years at all depths (Table 3). Treatments and their interactions were not significant for STN. Regardless of treatments, STN at all depths typically declined from 2006 to 2011. The rates of decline, based on the slope of linear regression of STN with time from 2006 to 2011, were 20, 12, 66, 160, 108, 89, 32, 96, 254, 360, and 449 kg N ha–1 yr–1, respectively, at 0 to 5, 5 to 10, 10 to 30, 30 to 60, 60 to 90, 90 to 120, 0 to 10, 0 to 30, 0 to 60, 0 to 90, and 0 to 120 cm (R2 = 0.35 to 0.67, P £ 0.21, n = 6). In underlying soil layers with similar thickness, rate of STN decline decreased with soil depth. The nonsignificant effects of treatments and interactions on STN show that soil N storage did not change even after 6 yr of soil and crop management practices under dryland cropping systems in the northern Great Plains. Franzluebbers et al. (1995) reported that STN changes slowly due to management practices because of its large pool size and inherent spatial variability. Ortega et al. (2002) reported that STN did not change even after Agronomy Journal • Volume 105, Issue 5 • 2013

Table 3. Effects of cropping sequence and N fertilization rate on soil total nitrogen (STN) content at the 0- to 120-cm depth from 2006 to 2011.

Year 2006 2007 2008 2009 2010 2011 Significance Cropping sequence (C) N fertilization rate (N) C×N C×N Year (Y) C ×Y N ×Y C × N ×Y

STN content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm ————————————————————————————— Mg N ha–1 ————————————————————————————— 1.15a† 0.97b 3.96a 4.70a 3.15a 3.05b 2.12b 6.08a 10.78a 13.93a 16.98a 1.12a 0.96bc 3.94a 4.67a 3.17a 3.03b 2.08b 6.02ab 10.69a 13.85a 16.89ab 1.14a 1.01a 4.00a 4.56a 3.15a 3.33a 2.14a 6.14a 10.70a 13.86a 17.14a 1.13a 0.97b 3.77b 4.20c 2.98b 3.47a 2.10ab 5.87b 10.07b 13.06b 16.53b 1.04b 0.90d 3.45c 3.68c 2.30c 2.26d 1.94c 5.39d 9.07c 11.37c 13.62d 1.06b 0.93cd 3.84ab 4.25b 2.95b 2.86c 1.99c 5.84c 10.10b 13.06b 15.92c ns‡ ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

ns *** ns ns ns

*** Significant at P £ 0.001. † Numbers followed by different letters within a column set are significantly different at P £ 0.05 by the least significant difference test. ‡ ns, not significant.

8 yr of crop rotation under dryland no-till cropping systems in the central Great Plains. Only after 12 yr, Sherrod et al. (2003) found increased STN with increased cropping intensity. Sainju et al. (2006, 2009) reported that harsh environmental conditions due to cold weather and limited precipitation, resulting in lower crop biomass N returned to the soil, reduced turnover rate of plant N to soil organic N under dryland cropping systems in semiarid regions of the northern Great Plains compared to humid regions in the United States. More than 6 yr of study may be needed to observe the effect of management practices in STN levels under dryland cropping systems. Declining levels of STN at all depths with year, regardless of treatments, however, suggest that tillage and reduced amount of crop biomass N returned to the soil probably reduced STN. Probably, the amount of crop biomass N returned to the soil is not enough to maintain STN level against mineralization of organic N. Greater rate of decline of STN in overlying than in underlying soil layers was probably related to higher STN concentration in overlying layers. Soil Ammonium Nitrogen Soil NH4–N content varied with N fertilization rates at 0 to 5 and 0 to 10 cm and with years at all depths (Table 4). Interaction was significant for cropping sequence × year at all depths, except at 0 to 5, 90 to 120, and 0 to 10 cm. In 2007, NH4–N content at all depths, except at 0 to 5, 90 to 120, and 0 to 10 cm, averaged across N rates, was greater in NTB–P than in CTB–F, NTB–F, or NTCB (Table 5). In 2008, NH4–N content at 30 to 60, 60 to 90, 0 to 90, and 0 to 120 cm was greater in NTB–F than in CTB–F, but at 5 to 10 cm was greater in NTCB than in NTB–P. In 2009, NH4–N content at 5 to 10, 30 to 60, 0 to 60, 0 to 90, and 0 to 120 cm was greater in NTB–P than in NTB–F or CTB–F. In 2010, NH4–N content at 5 to 10, 10 to 30, 0 to 30, 0 to 60, 0 to 90, and 0 to 120 cm was greater in CTB–F than in NTB–F or NTB–P. In 2011, NH4–N content at 0 to 60 cm was greater in CTB–F than in NTB–F.

The greater NH4 –N content at most depths in NTB–P than in other cropping sequences in 2007 and 2009 was probably due to increased mineralized N supplied by pea residue with higher N concentration than malt barley. Nitrogen concentration in pea residue from 2006 to 2011 averaged 12.9 g N kg–1 compared to 8.3 g N kg–1 in malt barley residue (Sainju et al., 2013). Similar increases in soil NH4 –N content at 0 to 20 cm in dryland cropping systems that included pea in rotation with spring wheat, hay barley, and corn (Zea mays L.) compared to spring wheat monocropping were previously reported (Sainju et al., 2009, 2012). Greater NH4 –N content in NTB–F than in other cropping sequences in 2008, a year with below-average precipitation (189 mm compared to the normal of 357 mm), however, could be due to reduced mineralization of NH4 –N to NO3–N as a result of lower soil water availability. In contrast, greater NH4 –N content in CTB–F than in NTB–F and NTB–P in 2010 and 2011, years with near or above-average precipitation (347–415 mm), could be due to increased N mineralization from crop residue and soil from increased tillage intensity and soil water availability. Averaged across cropping sequences and years, NH4 –N content at 0 to 5 and 0 to 10 cm was greater with 120 than with 0 and 40 kg N ha–1 (Table 4). Increased N rate likely increased NH4 –N content, especially at the surface layer. Averaged across treatments, NH4 –N content at multiple depths varied among years, but generally was greater from 2008 to 2011 than in 2006 and 2007. Accumulation of soil residual N from N fertilization to malt barley in previous years and/or increased N mineralization from crop residue and soil may have increased NH4 –N content in succeeding years, since STN content declined from 2006 to 2011 (Table 3). Nonsignificant effect of cropping sequence on NH4 –N content indicates that tillage, overall, did not affect its level.


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Table 4. Effects of cropping sequence and N fertilization rate on soil NH4 –N content at the 0- to 120-cm depth from 2006 to 2011. N fertilization rate kg N ha–1 0 40 80 120

Year

2006 2007 2008 2009 2010 2011 Significance Cropping sequence (C) N fertilization rate (N) C×N Year (Y) C ×Y N ×Y C × N ×Y

NH4–N content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm ————————————————————————————— kg N ha–1 ————————————————————————————— 2.4b† 2.5a 10.4a 15.8a 19.4a 23.8a 4.9b 15.3a 31.2a 50.2a 72.0a 2.3b 2.3a 10.6a 15.4a 19.7a 25.0a 4.7b 15.2a 30.6a 49.7a 72.7a 2.5b 2.5a 10.3a 15.5a 19.7a 25.1a 5.0ab 15.4a 30.8a 49.1a 72.2a 2.9a 2.6a 10.8a 16.2a 19.6a 25.7a 5.5a 16.1a 32.0a 50.8a 73.6a 2.1c 2.6b 2.5b 2.6b 2.4bc 3.0a

1.9c 2.0c 2.5b 2.9a 2.7ab 2.9a

8.8c 7.7c 10.8b 12.5a 11.9ab 11.5ab

11.1b 11.2b 17.5a 19.1a 17.4a 18.0a

14.5b 14.4b 23.3a 23.9a 22.1a nd‡

23.6b 17.3c 28.3a 26.3ab 28.9a nd

4.0d 4.7c 5.0b 5.5ab 5.1bc 5.9a

12.8c 12.3c 15.7b 18.1a 16.8ab 17.2ab

23.9c 23.6c 33.2b 37.1a 34.0ab 34.9ab

38.4b 38.0b 56.5a 61.1a 55.7a nd

52.1b 55.2b 84.5a 87.4a 83.9a nd

ns§ *** ns ** ns ns ns

ns ns ns *** * ns ns




ns ns ns *** ns ns ns

ns * ns *** ns ns ns


ns ns ns *** ** ns ns

ns ns ns *** ** ns ns

ns ns ns *** *** ns ns

* Significant at P £ 0.05. ** Significant at P £ 0.01. *** Significant at P £ 0.001. † Numbers followed by different letters within a column in a set are significantly different at P £ 0.05 by the least significant difference test. ‡ nd, not determined. § ns, not significant.

Table 5. Interaction of cropping sequence and year on soil NH4 –N content at the 0- to 120-cm depth averaged across N fertilization rates.

Year

Cropping sequence†

2006

2007

2008

2009

2010

2011

LSD (0.05)

CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB

NH4–N content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm —————————————————————————————— kg N ha–1 —————————————————————————————— 2.2 2.0 8.3 9.8 13.1 24.2 4.1 12.4 22.3 35.4 43.5 2.2 2.0 10.3 12.2 15.1 20.9 4.2 14.5 26.7 41.7 55.7 1.9 2.0 8.1 10.8 14.6 23.4 3.9 12.0 22.8 37.4 53.0 2.1 1.8 8.4 11.5 15.3 25.9 3.9 12.3 23.8 39.1 56.4 2.7 1.8 7.5 10.5 12.7 15.2 4.8 12.0 22.5 35.2 50.4 2.4 1.9 7.2 10.3 13.5 16.9 4.3 11.5 21.8 35.3 52.2 3.1 2.6 9.6 14.4 19.1 21.3 5.6 15.2 29.6 48.7 70.1 2.4 1.9 6.3 9.8 12.2 15.6 4.3 10.6 20.4 32.6 48.2 2.4 2.5 10.2 15.7 21.2 25.6 4.8 15.0 30.7 51.9 77.8 2.4 2.4 12.3 20.7 26.5 31.4 4.8 17.1 37.8 64.3 95.7 2.5 2.2 10.2 17.1 23.1 27.6 4.7 14.8 31.9 55.0 82.6 2.8 2.8 10.4 16.5 22.5 28.2 5.6 16.0 32.5 32.6 82.0 2.5 2.7 11.4 17.3 21.7 22.9 5.2 16.6 33.9 55.6 78.5 2.4 2.6 11.7 17.0 21.8 26.2 5.0 16.7 33.7 55.5 81.8 2.9 3.2 13.7 21.4 26.2 27.5 6.2 19.9 41.3 67.5 95.0 2.8 2.9 13.4 20.6 25.9 28.6 5.7 19.0 39.7 65.6 94.3 2.8 3.3 13.1 19.0 23.7 30.6 6.1 19.2 38.2 61.9 92.6 2.1 2.4 10.4 15.6 21.4 27.8 4.3 13.8 28.6 48.1 72.6 2.3 2.4 12.5 16.6 19.1 26.8 4.7 17.2 33.8 52.9 79.7 2.6 2.8 11.6 18.4 24.1 30.5 5.4 17.0 35.5 60.1 90.5 3.3 3.1 12.6 19.5 nd‡ nd 6.4 19.1 38.6 nd nd 2.8 2.7 10.7 15.8 nd nd 5.4 15.8 30.5 nd nd 3.0 2.7 11.2 18.0 nd nd 5.7 16.5 34.5 nd nd 3.0 2.9 11.5 18.7 nd nd 5.9 17.4 36.2 nd nd ns§ 0.6 2.7 3.9 5.1 ns ns 3.9 7.3 11.2 16.0

† Cropping sequences are CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; and NTCB, no-till continuous malt barley. ‡ Not determined. § Not significant.

1258


Table 6. Effects of cropping sequence and N fertilization rate on soil NO3 –N content at the 0- to 120-cm depth from 2006 to 2011. N Cropping fertilization sequence† rate Year kg N ha–1 CTB–F NTB–F NTB–P NTCB 0 40 80 120

Significance Cropping sequence (C) N fertilization rate (N) C×N Year (Y) C ×Y N ×Y C × N ×Y

NO3–N content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm ————————————————————————— kg N ha–1 ————————————————————————— 10.8a‡ 6.0a 20.2a 23.6a 24.4a 28.5a 16.8a 37.0a 60.6a 85.0a 112.7a 11.5a 4.9ab 17.2b 22.4a 20.6b 22.8a 16.4a 33.5a 55.9a 76.2a 98.3b 6.9b 3.6c 12.0c 14.8b 12.5c 15.1b 10.5b 22.5b 37.4b 49.8b 64.4c 7.9b 4.8b 15.2b 15.4b 12.8c 17.4b 12.6b 22.8b 43.1b 55.9b 72.2c 6.7c 8.1c 10.1b 12.2a

3.7c 4.3bc 5.1b 6.2a

13.3c 14.6c 16.7b 20.0a

15.5c 17.5bc 19.8b 23.4a

2006

2.7d

4.3b

28.9a

2007 2008 2009 2010 2011

9.7b 22.7a 5.0c 9.8b 5.7c

2.9c 11.2a 3.0c 4.4b 3.2c

10.4d 20.0b 14.5c 11.7d 11.5d ** *** ns *** * *** ns

** *** ns§ *** ns *** ns

* *** ns ** ** ** ns

13.7c 17.1b 17.7b 21.7a

16.7b 21.4ab 21.0ab 24.7a

10.2c 12.5c 15.2b 18.3a

23.6d 27.1c 31.9b 38.2a

39.0d 44.6c 51.8b 61.7a

52.7d 61.6c 69.4b 83.3a

32.8a

9.2c

14.1c 17.2c 23.5b 12.6d 14.1c

16.1b 23.2a 23.0a 17.9b 16.0b

10.7d

7.0a

35.8b

68.6a

77.8b

16.1cd 31.0a 24.3b 23.6b 20.1bc

12.6b 33.6a 8.0c 14.2b 9.0c

23.0cd 53.6a 22.5cd 25.7c 20.5d

37.1c 70.8a 46.0b 38.3c 34.6c

53.2c 94.1a 69.0b 56.1c 50.4c

** *** ns *** *** *** ns

** *** ns *** ** ns ns

* ** ns *** ** ns ns

** *** ns *** * *** ns

** *** ns *** ** *** ns

*** *** ns *** ** *** ns

*** ** ns *** ** *** ns

68.7c 82.3b 89.6b 107.0a 84.4bc 69.3d 124.7a 93.2b 79.7c 70.1d *** *** ns *** *** * ns

* Significant at P £ 0.05. ** Significant at P £ 0.01. *** Significant at P £ 0.001. † Cropping sequences are CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; and NTCB, no-till continuous malt barley. ‡ Numbers followed by different letters within a column in a set are significantly different at P £ 0.05 by the least significant difference test. § ns, not significant.

Soil Nitrate-Nitrogen Soil NO3–N content varied with cropping sequences, N fertilization rates, and years at all depths (Table 6). At all depths, interactions were significant for cropping sequence × year, except at 0 to 5 cm, and for N fertilization × year, except at 60 to 90 and 90 to 120 cm. Averaged across N rates, NO3–N content at almost all depths and years, except at 5 to 10, 10 to 30, 0 to 10, and 0 to 30 cm in 2008, was greater in CTB–F or NTB–F than in NTB–P and NTCB (Table 7). In 2008, NO3–N content at 5 to 10, 0 to 10, 10 to 30, and 0 to 30 was greater in NTCB than in CTB–F, NTB–F, or NTB–P. The greater NO3–N content in CTB–F and NTB–F than in other cropping sequences in all years, except in 2008, was probably due to N mineralization during fallow. Increased soil temperature and water content during fallow enhance soil microbial activity, thereby increasing N mineralization (Haas et al., 1974; Halvorson et al., 2002). Alternate-year fallow is often used to increase soil water and N availability that reduce N fertilization rate and the risk of crop failure compared to continuous cropping under dryland farming systems in the northern Great Plains (Aase and Pikul, 1995; Jones and Popham, 1997). Averaged across cropping sequences, NO3–N content was greater with 120 than with 0, 40, or 80 kg N ha–1 at almost all depths, except at 60 to 90 and 90 to 120 cm, from 2007 to

2011 (Table 8). The increases with 120 kg N ha–1 were greater in 2008 than in other years, especially at surface layers. While increased N rates increased NO3–N content at most depths and years, reduced N uptake by crops due to below-average precipitation may have increased soil NO3–N content in 2008. Averaged across N rates and years, NO3–N content was greater in CTB–F and NTB–F than in NTB–P and NTCB at all depths, except at 5 to 10 and 10 to 30 cm, where the content was greater in CTB–F than in NTB–P and NTCB (Table 6). Averaged across cropping sequences and years, NO3–N content increased with increased N rates at all depths. Averaged across treatments, NO3–N content was greater in 2008 than in other years at all depths, except at 10 to 30 and 30 to 60, where the content was greater in 2006 than in other years. While increased N mineralization due to fallow increased NO3–N content in CTB–F and NTB–F than in other cropping sequences, reduced or inefficient N uptake by crops may have increased NO3–N content with increased N rates. Similarly, reduced N uptake by crops during the dry period probably increased NO3–N content in 2008 compared to other years. As with STN and NH4 –N contents, nonsignificant difference in NO3–N content at 0 to 5 and 5 to 10 cm between CTB–F and NTB–F suggests that tillage did not affect soil NO3–N content at surface layers.


1259

Table 7. Interaction of cropping sequence and year on soil NO3 –N content at the 0- to 120-cm depth averaged across N fertilization rates.

Year

Cropping sequence†

2006

CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB CTB–F NTB–F NTB–P NTCB

2007

2008

2009

2010

2011

LSD (0.05)

NO3–N content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm —————————————————————————————— kg N ha–1 —————————————————————————————— 3.0 5.7 33.4 31.5 10.3 7.3 8.7 42.1 73.6 83.8 86.3 2.6 3.2 28.1 33.3 8.8 8.4 5.8 33.8 67.1 75.9 81.4 2.9 4.1 23.2 30.6 7.8 9.5 7.0 30.1 60.7 68.4 74.9 2.3 4.2 30.8 35.8 10.0 17.7 6.5 37.3 73.1 83.0 95.0 11.4 4.1 13.8 20.9 22.9 21.7 15.5 29.4 50.3 73.2 94.9 14.4 3.6 13.0 16.7 17.9 18.1 18.0 31.0 47.8 65.6 83.7 4.9 1.7 6.3 9.9 11.9 11.7 6.6 12.9 22.8 34.7 76.3 8.1 2.2 8.6 8.9 11.6 12.9 10.3 18.8 27.2 39.3 52.2 22.8 11.3 21.0 16.9 29.9 41.4 33.7 54.6 71.5 101.4 142.8 26.1 10.2 20.8 22.6 28.5 35.6 36.3 57.1 79.7 108.2 143.8 19.1 8.0 15.0 14.3 15.8 21.5 27.1 42.1 56.4 72.1 93.6 22.7 15.2 23.2 15.2 18.8 25.6 37.3 60.5 75.6 94.5 118.8 7.0 4.2 20.5 36.3 37.5 41.8 11.2 31.6 67.9 105.4 147.3 8.3 4.1 14.5 30.3 31.9 26.3 12.4 26.9 57.2 89.2 115.5 2.7 2.1 11.1 12.8 10.8 13.6 4.7 15.8 28.9 39.4 52.9 2.0 1.7 11.9 14.6 11.5 15.3 3.7 15.7 30.3 41.8 57.1 12.2 5.5 15.3 16.0 23.9 35.4 17.8 33.1 49.1 73.0 108.4 11.9 5.2 14.1 15.1 20.9 27.6 16.9 30.6 45.7 66.3 93.9 7.6 3.5 8.9 10.6 14.5 14.5 11.1 20.0 30.6 45.2 59.7 7.3 3.5 8.5 8.6 12.3 16.7 10.8 19.3 27.9 40.1 56.9 8.5 5.2 17.5 19.9 22.1 23.6 13.7 31.2 51.1 73.2 96.5 5.7 3.0 12.5 16.4 15.5 20.8 8.8 21.4 38.0 52.3 71.6 4.0 2.3 7.9 11.1 13.9 19.8 6.3 14.2 25.2 39.2 58.9 4.8 2.2 8.2 9.0 12.6 16.2 7.0 15.2 24.2 36.8 53.3 4.0 2.1 4.7 6.5 7.2 13.9 5.4 8.7 12.9 18.4 24.0

† Cropping sequences are CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB-P, no-till malt barley–pea; and NTCB, no-till continuous malt barley.

Table 8. Interaction of N fertilization rate and year on soil NO3 –N content at the 0- to 120-cm depth averaged across cropping sequences.

Year 2006

2007

2008

2009

2010

2011

N fertilization rate kg N ha–1 0 40 80 120 0 40 80 120 0 40 80 120 0 40 80 120 0 40 80 120 0 40 80 120

LSD (0.05)

NO3–N content at the soil depth 0–5 5–10 10–30 30–60 60–90 90–120 0–10 0–30 0–60 0–90 0–120 cm cm cm cm cm cm cm cm cm cm cm —————————————————————————————— kg N ha–1 —————————————————————————————— 2.7 4.3 29.0 32.8 9.2 10.7 7.0 36.5 68.6 77.8 84.4 2.7 4.3 28.7 32.6 9.1 10.5 7.0 35.9 68.2 77.3 84.5 2.6 4.1 28.9 32.7 9.0 10.8 7.1 35.7 68.3 77.5 84.3 2.5 4.3 28.9 32.8 9.3 10.6 6.9 35.8 68.4 77.7 84.4 7.0 2.3 8.2 11.5 13.9 14.9 9.4 17.5 29.0 42.9 57.8 8.2 2.6 8.7 11.8 14.3 15.8 10.8 19.5 31.3 45.6 61.4 10.7 3.1 10.8 15.8 17.9 16.5 13.8 24.7 40.5 58.4 74.9 12.9 3.5 14.0 17.3 18.1 17.1 16.4 30.4 47.8 65.9 83.0 14.2 6.8 12.7 11.7 18.5 22.4 20.0 32.7 44.4 62.8 85.2 19.9 9.9 18.3 17.2 25.6 32.1 29.8 48.1 65.3 91.0 123.1 26.3 11.4 20.2 16.7 22.3 30.9 37.7 57.9 74.6 96.9 127.8 30.3 16.6 28.8 23.4 26.5 38.8 46.9 76.7 67.9 125.6 163.0 4.3 2.5 9.3 12.9 16.0 20.7 6.8 16.2 29.0 45.0 65.7 4.4 2.6 10.1 17.4 24.2 27.1 7.0 17.1 34.5 58.9 85.8 5.4 3.7 16.8 26.7 22.9 24.2 9.0 25.9 52.6 75.5 99.7 5.8 3.2 21.7 37.1 28.8 25.0 9.1 30.8 67.9 96.6 121.6 7.7 3.9 10.3 11.2 11.8 17.0 11.6 21.9 33.0 44.9 61.9 9.6 4.3 11.5 11.9 13.9 24.4 13.9 25.4 37.3 51.1 75.6 9.6 4.8 12.1 12.7 17.0 22.0 14.4 26.4 39.2 56.1 78.1 12.2 4.8 12.8 14.4 29.0 30.9 16.9 29.2 43.6 72.5 103.3 4.2 2.5 10.6 12.7 12.9 14.8 6.7 17.3 30.1 43.0 57.4 3.8 2.4 10.2 14.0 15.6 18.1 6.2 16.4 30.3 45.7 63.6 5.9 3.2 11.4 14.3 17.0 21.6 9.1 20.6 35.1 51.4 72.9 9.1 4.7 13.9 15.4 18.7 25.7 13.7 27.5 43.1 61.5 86.4 3.9

2.0

4.5

6.4

ns†

ns

5.5

8.3

13.1

18.6

24.5

† ns, not significant.

1260


Table 9. Effects of cropping sequence and N fertilization rates on the estimated N balance as a result of N fertilization to crops, total annualized N removed in grains from 2006 to 2011, surface residue N in 2011, and soil total nitrogen (STN) content at the 0to 120-cm depth at the beginning (2006) and end (2011) of the experiment. Cropping N fertilization Total N fertilizer Total N removed Soil surface Estimated N sequence† rate Initial STN (A) applied (B) in grains (C) residue N (D) Final STN (E) balance (F)‡ ——————————————————————————————— kg N ha–1 ——————————————————————————————— CTB–F 0 16,980 0 159 15 15,834 –972 40 16,980 112 168 16 16,083 –825 80 16,980 272 186 16 16,491 –559 120 16,980 441 192 18 16,123 –1088 NTB–F 0 16,980 0 132 19 15,418 –1411 40 16,980 122 168 20 15,212 –1702 80 16,980 287 174 18 16,520 –555 120 16,980 494 183 21 16,080 –1190 NTB–P 0 16,980 0 246 20 16,000 –714 40 16,980 123 264 18 16,958 137

NTCB

80 120 0 40 80 120

16,980 16,980 16,980 16,980 16,980 16,980 —

300 480 0 121 312 479 105

330 354 204 246 288 324 58

19 20 14 18 20 23 ns§

16,347 15,575 15,022 15,820 15,915 15,450 ns

–584 –1511 –1740 –1017 –1069 –1662 635

0 40 80 120

16,980 16,980 16,980 16,980

0d¶ 120c 293b 474a

185c 212bc 245ab 263a

14c 16b 18b 21a

15,569a 16,018a 13,618a 15,807a

–1209b –852a –692a –1378b

** *** *

* *** ns

ns ns ns

ns *** *

LSD (0.05) Means

Significance Cropping sequence (C) N fertilization rate (N) C×N

– – –

ns *** ***

* Significant at P £ 0.05. **Significant at P £ 0.01. *** Significant at P £ 0.001. † Cropping sequences are CTB–F, conventional till malt barley–fallow; NTB–F, no-till malt barley–fallow; NTB–P, no-till malt barley–pea; and NTCB, no-till continuous malt barley. ‡ Estimated N balance (F) = Column (C) + (D) + (E) – (A) – (B). § ns, not significant. ¶ Numbers followed by different letters within a column in a set are significantly different at P £ 0.05 by the least significant difference test.

Nitrogen Balance Differences in the amount of N fertilizer applied to malt barley, total annualized amount of N removed by malt barley and pea grains from 2006 to 2011, and final surface residue N and STN levels in 2011 resulted in variations in estimated N balance among treatments (Table 9). Although the total amount of N fertilizer applied to malt barley from 2006 to 2011 increased with increased N rates, the amount varied in each cropping sequence because N rates were adjusted to soil NO3–N to a depth of 60 cm determined in the fall of the previous year. Total N removed in malt barley and pea grains from 2006 to 2011 was greater with 80 and 120 than with 0 and 40 kg N ha–1 in NTB–P and greater with 120 than with 0 and 40 kg N ha–1 in NTCB. With or without N fertilization, total N removed in grains was greater in NTB–P and NTCB than in CTB–F and NTB–F, a result of increased annualized yield due to continuous cropping vs. crop fallow. Soil surface residue N in 2011 contributed a small portion of N for calculating N balance. It was assumed that N added through precipitation

in each year was small and negligible and that the amount was similar in each treatment. Estimated N balance was negative in all treatments, except in NTB–P with 40 kg N ha–1, which has significantly greater N balance than in other treatments (Table 9). Nitrogen balance was greater with 40 or 80 kg N ha–1 than with other N rates in NTB–F and NTB–P. Similarly, N balance was greater with 40 than with 0 and 120 kg N ha–1 in NTCB. With 0 kg N ha–1, N balance was greater in NTB–P than in NTB–F and NTCB. With 40 kg N ha–1, N balance was greater in NTB–P than in other cropping sequences. Averaged across cropping sequences, N balance was greater with 40 and 80 than with 0 and 120 kg N ha–1. Greater N balance with 40 or 80 kg N ha–1 than with other N rates in NTB–F and NTB–P likely resulted from increased STN, followed by similar or higher grain N removal, and/ or lower amount of N fertilizer applied. Optimum rate of N fertilization increased grain N uptake and STN compared to no N fertilization, resulting in greater N balance. In contrast, excessive N fertilization may have increased soil N loss due to


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leaching, volatilization, and denitrification without altering STN and grain N uptake, resulting in lower N balance. Greater N balance in NTB–P than NTB–F and NTCB at 0 and 40 kg N ha–1 suggests that increased N supplied by pea residue may have increased N balance in NTB–P at reduced or no N rates. Negative N balance in most treatments suggests that N loss can occur even during periods outside growing seasons, a case previously reported by several researchers for dryland cropping systems in the northern Great Plains (Sainju and Lenssen, 2011, Sainju et al., 2009, 2012). Greater N balance in NTB–P with 40 kg N ha–1 than in other treatments was probably a result of higher STN in 2011 and lower amount of N fertilizer applied to malt barley than other cropping sequences with 80 and 120 kg N ha–1. Because of lower C/N ratio than malt barley, pea may have increased turnover of plant N to soil N, thereby increasing STN while reducing the amount of N fertilizer to sustain crop yields in this treatment. Several researchers (Sainju and Lenssen, 2011; Sainju et al., 2012) also reported greater N balance in crop rotations containing legumes, such as pea, than in continuous nonlegume monocropping. In contrast, lower STN, followed by increased N loss due to leaching, volatilization, and denitrification, probably resulted in lower N balance in other treatments. Positive and greater N balance in NTB–P with 40 kg N ha–1 compared to negative and lower values in other treatments shows that no-till malt barley–pea rotation with reduced N fertilization rate can gain N by increasing N storage and decreasing N fertilization rate instead of N losses through soil processes in other management practices. This management practice also produced similar or better malt barley yield and quality compared to NTCB with 80 and 120 kg N ha–1 (Sainju et al., 2013). Therefore, NTB–P with 40 kg N ha–1 may be used as a management option to reduce N losses through leaching, volatilization, and denitrification in dryland malt barley production in the northern Great Plains. CONCLUSIONS Differences in the amount of crop biomass N returned to the soil, their placement in the soil due to tillage, and N fertilization rates among treatments from 2006 to 2011 influenced surface residue and soil N and estimated N balance. As hypothesized, NTB–P with 40 kg N ha–1 increased estimated N balance compared to other treatments by increasing soil N storage. While NTB–P had greater crop biomass N, NTCB had higher surface residue N than other cropping sequences. Soil NH4–N content varied among cropping sequences, but NO3–N content was greater in CTB–F than in other cropping sequences at most depths and years. Increased N fertilization rate increased crop biomass N, surface residue N, and soil NH4–N and NO3–N contents. Tillage had minor influence on crop biomass N and STN. Estimated N balance after accounting for all sources and sinks of N was greater in NTB–P with 40 kg N ha–1 than in other treatments. As a result, no-till malt barley–pea rotation with reduced N fertilization rate (40 kg N ha–1) may be used as a management option to reduce N losses through leaching, volatilization, denitrfication, and N2O emissions without influencing crop yields and quality for dryland malt barley cropping systems in the northern Great Plains. 1262

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