Increased crop diversity and length of rotation may improve corn (Zea mays L.) yield and water-and nitrogen-use efficiency (WUE and NUE). The objectives of this study were to determine effects of crop rotation on corn yield, water use, and nitrogen (N) use. No-tillage (NT) crop rotations were started in 1997 on a Barnes clay loam (fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, S. D. Rotations were continuous corn (CC), corn-soybean [Glycine max (L.) Merr.] (CS), a 3-year rotation of corn-soybean-oat/pea (Avena sativa L. and Pisum sativum L.) hay (CSH), a 3-year rotation of corn-soybean-spring wheat (Triticum aestivum L.) (CSW), and a 5-year rotation of corn-soybean-oat/pea hay companion seeded with alfalfa (Medicago sativa L.)-alfalfa-alfalfa (CSHAA). Fertilizer N was applied to corn on all rotations at planting (16 kg N ha(-1)) and side-dressed (64 kg N ha(-1)). Average corn grain yields (1998-2007) were greatest under CSW (7.38 Mg ha(-1)) and least under CC (4.66 Mg ha(-1)). Yields were not different among CSH, CSW, and CSHAA rotations. Water-use efficiency of rotation was ordered as CSW > CSH > CSHAA > CS > CC. Nitrogen-use efficiency was greatest under CSW and least under CC. There were no differences in yield advantage (YA) among crop rotations during years with plentiful early-season rainfall (May 1-July 31). In years with low spring rainfall, YA was greatest under CSW (54%) and least under CSHAA (33%). Corn yields under extended rotations (CSH, CSW, and CSHAA) were greater than under CC and CS, but lack of rainfall may result in reduced yields under CSHAA.

Abstract Agricultural systems produce both detrimental and beneficial effects on soil quality (SQ). We compared soil physical properties of long-term conventional (CON) and alternative (ALT) cropping systems near Akron, Colorado (CO); Brookings, South Dakota (SD); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan (ND); Mead, Nebraska (NE); Sidney, Montana (MT); and Swift Current, Saskatchewan (SK), Canada. Objectives were to quantify the changes in soil physical attributes in cropping systems and assess the potential of individual soil attributes as sensitive indicators of change in SQ. Soil samples were collected three times per year from each treatment at each site for one rotation cycle (4 years at Brookings and Mead). Water infiltration rates were measured. Soil bulk density (BD) and gravimetric water were measured at 0–7.5, 7.5–15, and 15–30 cm depth increments and water-filled pore space ratio (WFPS) was calculated. At six locations, a rotary sieve was used to separate soil (top 5 cm) into six aggregate size groups and calculate mean weight diameter (MWD) of dry aggregates. Under the CON system at Brookings, dry aggregates (>19 mm) abraded into the smallest size class (<0.4 mm) on sieving. In contrast, the large aggregates from the ALT system abraded into size classes between 2 and 6 mm. Dry aggregate size distribution (DASD) shows promise as an indicator of SQ related to susceptibility of soil to wind erosion. Aggregates from CON were least stable in water. Soil C was greater under ALT than CON for both Brookings and Mead. At other locations, MWD of aggregates under continuous crop or no tillage (ALT systems) was greater than MWD under CON. There was no crop system effect on water infiltration rates for locations having the same tillage within cropping system. Tillage resulted in increased, decreased, or unchanged near-surface BD. Because there was significant temporal variation in water infiltration, MWD, and BD, conclusions based on a single point-in-time observation should be avoided. Elevated WFPS at Fargo, Brookings, and Mead may have resulted in anaerobic soil conditions during a portion of the year. Repeated measurements of WFPS or DASD revealed important temporal characteristics of SQ that could be used to judge soil condition as affected by management.

Abstract Soil management and cropping systems have long-term effects on agronomic and environmental functions. This study examined the influence of contrasting management practices on selected soil chemical properties in eight long-term cropping system studies throughout the Great Plains and the western Corn Belt. For each study, soil organic C (SOC), total N (TN), particulate organic matter (POM), inorganic N, electrical conductivity (EC), and soil pH were evaluated at 0–7.5, 7.5–15, and 15–30 cm within conventional (CON) and alternative (ALT) cropping systems for 4 years (1999–2002). Treatment effects were primarily limited to the surface 7.5 cm of soil. No-tillage (NT) and/or elimination of fallow in ALT cropping systems resulted in significantly (P<0.05) greater SOC and TN at 0–7.5 cm within five of the eight study sites [Akron, Colorado (CO); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan, ND; and Swift Current, Saskatchewan (SK), Canada]. The same pattern was observed with POM, where POM was significantly (P<0.05) greater at four of the eight study sites [Bushland, TX, Mandan, ND, Sidney, Montana (MT), and Swift Current, SK]. No consistent pattern was observed with soil EC and pH due to management, although soil EC explained almost 60% of the variability in soil NO3-N at 0–7.5 cm across all locations and sampling times. In general, chemical soil properties measured in this study consistently exhibited values more conducive to crop production and environmental quality in ALT cropping systems relative to CON cropping systems.

Soils perform a number of essential functions affecting management goals. Soil functions were assessed by measuring physical, chemical, and biological properties in a regional assessment of conventional (CON) and alternative (ALT) management practices at eight sites within the Great Plains. The results, reported in accompanying papers, provide excellent data for assessing how management practices collectively affect agronomic and environmental soil functions that benefit both farmers and society. Our objective was to use the regional data as an input for two new assessment tools to evaluate their potential and sensitivity for detecting differences (aggradation or degradation) in management systems. The soil management assessment framework (SMAF) and the agro-ecosystem performance assessment tool (AEPAT) were used to score individual soil properties at each location relative to expected conditions based on inherent soil-forming factors and to compute index values that provide an overall assessment of the agronomic and environmental impact of the CON and ALT practices. SMAF index values were positively correlated with grain yield (an agronomic function) and total organic matter (an agronomic and environmental function). They were negatively correlated with soil nitrate concentration at harvest (an indicator of environmental function). There was general agreement between the two assessment tools when used to compare management practices. Users can measure a small number of soil properties and use one of these tools to easily assess the effectiveness of soil management practices. A higher score in either tool identifies more environmentally and agronomically sustainable management. Temporal variability in measured indicators makes dynamic assessments of management practices essential. Water-filled pore space, aggregate stability, particulate organic matter, and microbial biomass were sensitive to management and should be included in studies aimed at improving soil management. Reductions in both tillage and fallow combined with crop rotation has resulted in improved soil function (e.g., nutrient cycling, organic C content, and productivity) throughout the Great Plains.

American Entomologist • Volume 51, Number 4 The Latin phrase ceteris paribus translates into English as “all other things being equal.” The ceteris paribus concept is central to the application of the scientifi c method, but it becomes problematic in the study of sustainability issues in complex agricultural systems that are adaptive and continually changing over time (Giampietro 2004). Factors other than those to be experimentally controlled and that are assumed to be consistent with ceteris paribus by experimental design may not actually be so because they are unrecognized or because they change during or after the experiment, rendering the interpretation of data fl awed or inapplicable. The ceteris paribus concept was implicitly assumed as appropriate and applicable to two studies that we recently undertook, in which ground beetles were treated as indicators of the sustainability and the benign character of certain management practices in a corn–soybean system.

Crop rotation may improve production efficiency and reduce fertilizer N requirements for corn ( Zea mays L.). Objectives were to determine effect of rotation and N on corn yield, efficiency of water use (WUE) and N use (NUE), and corn rootworm (Coleoptera: Chrysomelidae) beetle populations (CR). Rotations (started in 1990) were continuous corn (CC), corn–soybean [ Glycine max (L.) Merr.] (CS), and a 4‐yr rotation of corn–soybean–spring wheat ( Triticum aestivum L.) companion‐seeded with alfalfa ( Medicago sativa L.)–alfalfa hay (CSWA). Nitrogen treatments for corn were corn fertilized for a grain yield of 8.5 Mg ha −1 (highN), 5.3 Mg ha −1 (midN), and no N fertilizer (noN). Average yield (1992–2003) was greatest ( p = 0.003) under CS and highN (7.0 Mg ha −1 ). Yield differences ( p = 0.001) among rotations increased with decreased fertilizer N. Average (1992–2003) yield with noN fertilizer was 5.8 Mg ha −1 under CSWA, 4.5 Mg ha −1 under CS, and 2.8 Mg ha −1 under CC. Nitrogen use efficiency differed ( p = 0.096) only under midN with CSWA = CS > CC. Soil water (upper 1.8 m) for corn measured on 1 June (average of N treatments) was 55, 54, and 45 cm for CC, CS, and CSWA, respectively. For CSWA under highN, available water limited yield in 3 of 6 yr. At highN, CR adult populations were greater under CS compared with CC and greater at higher N fertilizer levels within CC. Rotations have potential to improve production efficiency; however, there is potential for reduced corn yield after alfalfa due to less available soil water.

Suitability of alternative crops in the northern Great Plains remains a question because of water limitations. Objectives were to compare water use of an oat (Avena sativa L.)-pea (Pisum sativum L.) mix grown for hay (OPH) to that of black lentil (Lens culinaris Medikus cv. Indianhead) grown as green manure (BL). Water use and plant biomass for OPH and BL were measured near Culbertson, MT (Site 1), during 4 yr. Soil water was measured by neutron attenuation. Precision-weighing lysimeters were used at Site 2, located 65 km southeast of Site 1, to measure water use. Soil was a Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustolls). Biomass of crops was measured biweekly. Relative feed value (RFV) based on measured neutral detergent fiber and acid detergent fiber was calculated. Biomass under OPH was 34 and 46% greater than with BL at Sites 1 and 2, respectively. At Site 1, biomass accumulated at a rate of 14 kg ha(-1)mm(-1)water used under BL and 23 kg ha(-1)mm(-1)under OPH. Biomass accumulated at a rate of 21 kg ha(-1)mm(-1) under BL and 29 kg ha(-1)mm(-1) under OPH at Site 2. Hay RFV, at full bloom in pea, averaged 116 (Number 2 hay), and this did not change appreciably as the crop matured to soft dough stage in oat. Oat-pea hay fits the growing conditions in the northern Great Plains and meets the needs of producers for high quality hay.

Abundance and head capsule width were measured for northern (Diabrotica barberi Smith & Lawrence) and western corn rootworm (D. virgifera virgifera LeConte) larvae recovered primarily from maize root systems but also from large soil cores each centered around a root system. Larvae for measurement derived from field populations under infestation and rotation regimes that allowed most specimens to be assigned to species. A frequency distribution of head capsule widths indicated three separate peaks for western corn rootworm, presumably representing frequency of the three larval instars, with no larvae measuring 280 or 420 microm in the valleys between peaks. Multiple normal curves fit to similar but partially overlapping peaks generated by northern corn rootworm suggested that division of first to second and second to third instar can best be made for this species at 267 and 406 microm, respectively (270 and 410 when measurements are made to the nearest 20 microm). These results implied that instar of individuals from mixed northern and western corn rootworm populations can be accurately judged from head capsule width without having to determine species. The relative abundance of western corn rootworm instars was similar in root systems removed from the center of 19-cm diameter x 19-cm deep soil cores and in soil cores from which the root systems were removed. Furthermore, the number of larvae from root systems correlated significantly with that from the surrounding soil. These results indicated that the former and much more convenient sampling unit can be used to estimate population developmental stage and possibly density, at least early in the season when these tests were done and young larvae predominated.

Benefits of subsoiling are difficult to predict. Objectives were to (i) determine effect of subsoiling on water infiltration and storage and (ii) evaluate longevity of tillage-induced soil structure. Experiments were conducted during two years and on two soils that were not subsoiled (NoSS), subsoiled (SS), and subsoiled plus secondary tillage (SSplus). Soils were Dooley fine sandy loam and Williams loam (fine-loamy, mixed, superactive, frigid Typic Argiustolls) near Culbertson, MT. Subsoiling, to a depth of 0.3 m, in Exp. 1 was with a paratill and with parabolic shanks in Exp. 2. Secondary tillage was with a disk in Exp. 1 and with sweeps in Exp. 2. Infiltration was measured using a sprinkler infiltrometer. Final infiltration rate, after two simulated storms, was 14 mm h−1 on NoSS, 29 mm h−1 on SS, and 7 mm h−1 on SSplus. Penetration resistance (PR) measurements suggest that soil subsidence following simulated rainstorms was less on treatments with no secondary tillage. Average water drainage from the 1.83-m profile was 1.4 mm h−1 during the first 3 d after water application. Average drainage was 0.23 mm h−1 during Days 3 to 7 and 0.09 mm h−1 during Days 7 to 15. Regardless of improved water infiltration under SS, all soil profiles (1.83 m deep) drained to ≈444 mm of water in 15 d. Results reveal a difficult soil management problem. Subsoiling initially improves infiltration, but no additional water storage was discernable after 15 d. Further, excess water percolation has potential to leach nitrate-N from the profile.

Ridge tillage (RT) has been proposed as an economically viable conservation tillage alternative for row crop production; however the long-term economic viability of RT in the northern Corn Belt of the USA is largely unknown. Economic returns, risk and input use were compared for RT and conventional tillage (CT) in a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation with high, medium and low nitrogen treatments. The analysis was based on 10 years of experimental data from Brookings, SD on a Barnes clay loam (US soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll; FAO classification: Chernozem). Economic returns were significantly higher at the highest nitrogen treatment levels. Highest average net returns to land and management were $ 78 per hectare for RT at the high nitrogen treatment level (RT-H) followed by $ 59 per hectare for CT at the high nitrogen treatment level (CT-H). Risk, measured as the standard deviation of net returns, was the lowest for CT at the medium nitrogen treatment level (CT-M) followed by RT-H and CT-H. However, net returns were substantially lower under CT-M at $ 32 per hectare. Average yields and average operating costs were not significantly different for RT-H and CT-H. Reduced equipment operating costs for CT-H were offset by increased herbicide costs for RT-H. Equipment ownership costs were significantly lower for RT-H than CT-H. There were no significant differences in fertilizer use for RT and CT. Pesticide use was significantly higher for RT-H than CT-H. Fuel use was 18–22% lower and labor use was 24–27% lower for RT-H than CT-H. Despite continued low adoption rates for RT in the northern Corn Belt, our analysis shows that RT is an economically viable alternative to CT.

Fertilizing soybeans (Glycine max (L.) Merrill) is not an entirely new concept; for a number of years, scientists have investigated the effect of nitrogen (N) fertilizer on yield and quality of soybeans. The objective of this research was to investigate the effect of starter fertilizer N rates and sources on soybean yield, protein, and oil content in the cool soils of the Northern Great Plains. A field experiment was established within a two-year corn (Zea mays L.) soybean rotation. Using a split-plot design with four replications. Whole plots were no-till (NT) and conventional tillage (CT) and the split plots were starter fertilizer (two sources x four rates) treatments. Nitrogen sources were either ammonium nitrate (AN) or urea (UR) each applied at 0,7.8, 15.7, and 23.5 kg N ha-l. Grain yields were higher for 2000 growing season compared to 2001 largely due to differences in rainfall. A yield reduction resulted from the 7.8 kg N hal rate during 2000. Maximum yield occurred at the 23.5 kg N hal AN treatment. Application of UR had no significant effect on grain yield regardless of N rate. The only yield difference for the 2001 season was between the tillage treatments. Similar to 2000 data the 7.8 kg N hal AN treatment had the lowest yield with maximum yield occurring at the 23.5 kg N hal AN treatment. but the difference was not significant. We speculate that the former results could be due to a decrease in nodulation in the early growth stages and subsequent decrease in N fixation. Perhaps the 15.7 and 23.5 kg treatments provided enough soil N to overcome a delay in nodulation. Similar to the yield data, the 7.8 kg N hal AN rate had the lowest N concentration, with the 15.7 kg N ha1 AN rate having the highest. Oil content was significantly affected by tillage and N rate with the NT resulting in higher oil content. There was no significant difference for N concentration or oil content for 2001. Although there were few significant differences in the 2001 growing season and the differences in the 2000 were small, it is important to note that applying N as starter has the potential to increase soybean yield and quality when soil temperatures are cool.

Corn grown under annual corn-soybean crop rotation has greater accumulation of certain mineral nutrients and higher yields than corn grown in monoculture. This study was conducted to determine if complex crop rotations (with legumes in the rotation as alfalfa hay as well as soybean row crops) and different levels of agriculture chemical input affect soil fertility and corn mineral nutrient composition. The effects of crop rotation [monoculture corn, corn-soybean 2-yr rotation, cornsoybean-wheat underseeded with alfalfa-alfalfa 4-yr rotation] and input level [high input (fertilizer application for 8.15 Mg hai yield goal, prophylactic herbicide and insecticide application, fall moldboard plow/spring disk and cultivation operations), intermediate input (fertilizer application for 5.33 Mg haI yield goal, pesticide applications based upon pest survey and IPM principles, fall chisel plow/spring disk and cultivation operations), and low input (no fertilizer, herbicide, or insecticide applications, fall chisel plow/spring disk and cultivation operations)] on soil fertility (pH, organic matter, N03-N, P, K, and total N) and on corn shoot dry weight, mineral nutrient (N, P, Ca, Mg) concentration and accumulation at tassel stage of development were investigated at Brookings, SD. Soil samples taken at the V6 stage of corn development indicated that crop rotation treatments reduced soil pH, increased soil N03-N level, and decreased soil P level when compared to corn monoculture. Shoots of plants grown under either 2-yr rotation intermediate input or 4-yr rotation no input treatments had greater dry weight, as well as greater P, Ca, and Mg accumulation than these same input treatments in other rotations. These results demonstrate a beneficial effect of crop rotation upon soil fertility and corn mineral nutrition. The results of this experiment are discussed in terms of nutrient synergisms whereby nutrient absorption proceeds at a faster rate than dry weight accumulation.

Ridge tillage is a special conservation tillage method, but the long-term effect of this tillage system on crop yield and soil quality in a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation is largely unknown in the northern Corn Belt of the USA. Our objectives were to compare crop performance and soil condition at three nitrogen-fertilizer levels under ridge tillage (RT) and conventional tillage (CT). The experiment was started in 1990 at Brookings, SD, on a Barnes clay loam (US soil taxonomy: fine-loamy, mixed Udic Haploboroll; FAO classification: Chernozem). CT included moldboard or chisel plowing, seedbed preparation with tandem disk and field cultivator, and row cultivation. Raised beds under RT were maintained using only row cultivation. Corn grain yield was significantly (p≤0.10) greater on CT than on RT. Average (11 years and three fertilizer-N rates) corn yield was 6267kgha−1 with RT and 6500kgha−1 with CT. Soybean grain yield was not significantly (p≤0.10) different between RT and CT. Average (11 years and three fertilizer-N rates) soybean yield was 1997kgha−1 with RT and 2058kgha−1 with CT. In 9 of 11 years there was a significant soybean-yield response to N-starter fertilizer. There was no significant accumulation of NO3-N in the top 3m of soil at the end of 9 years in either tillage treatment (111kgNO3-Nha−1 under RT and 121kgNO3-Nha−1 under CT). Soil pH in the top 15cm was unaffected by tillage (average pH was 6.62). In 1999, soil organic C in the top 0.2m was significantly greater under CT (56Mgha−1) than under RT (52Mgha−1). Bulk density in the top 0.2m was significantly greater under RT (1.52gcm−3) than under CT (1.44gcm−3). Tillage did not have a great effect on grain yield or soil properties. RT can protect soil from erosion because crop residues remain relatively undisturbed on the soil surface in contrast to chisel plow. In this respect, we expect RT to be more sustainable over the long term than chisel plow tillage.

Diversified crop rotation may improve production efficiency, reduce fertilizer nitrogen (N) requirements for corn (Zea mays L.), and increase soil carbon (C) storage. Objectives were to determine effect of rotation and fertilizer N on soil C sequestration and N use. An experiment was started in 1990 on a Barnes clay loam (U.S. soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, SD. Tillage systems for corn-soybean ( Glycine max [L.] Merr.) rotations were conventional tillage (CS) and ridge tillage (CSr). Rotations under conventional tillage were continuous corn (CC), and a 4-year rotation of corn-soybean-wheat ( Triticum aestivum L.) companion-seeded with alfalfa ( Medicago sativa L.)-alfalfa hay (CSWA). Additional treatments included plots of perennial warm season, cool season, and mixtures of warm and cool season grasses. N treatments for corn were corn fertilized for a grain yield of 8.5 Mg ha(-1) (highN), of 5.3 Mg ha(-1) (midN), and with no N fertilizer (noN). Total (1990-2000) corn grain yield was not different among rotations at 80.8 Mg ha(-1) under highN. Corn yield differences among rotations increased with decreased fertilizer N. Total (1990-2000) corn yields with noN fertilizer were 69 Mg ha-1 under CSWA, 53 Mg ha(-1) under CS, and 35 Mg ha(-1) under CC. Total N attributed to rotations (noN treatments) was 0.68 Mg ha(-1) under CSWA, 0.61 Mg ha(-1) under CS, and 0.28 Mg ha(-1) under CC. Plant carbon return depended on rotation and N. In the past 10 years, total C returned from above- ground biomass was 29.8 Mg ha(-1) under CC with highN, and 12.8 Mg ha(-1) under CSWA with noN. Soil C in the top 15 cm significantly increased (0.7 g kg(-1)) with perennial grass cover, remained unchanged under CSr, and decreased (1.7 g kg(-1)) under CC, CS, and CSWA. C to N ratio significantly narrowed (-0.75) with CSWA and widened (0.72) under grass. Diversified rotations have potential to increase N use efficiency and reduce fertilizer N input for corn. However, within a corn production system using conventional tillage and producing (averaged across rotation and N treatment) about 6.2-Mg ha(-1) corn grain per year, we found no gain in soil C after 10 years regardless of rotation.

Wheat (Triticum aestivum L.) is the major crop on semiarid northern Great Plains of the USA. Attempts to introduce alternate crops have had limited success. Alternate fallow-spring wheat rotation is the most common cultural practice. Our objective was to investigate water use and water use efficiency and suitability of alternative crops in semiarid northern Great Plains agricultural environment. The study was on glacial till Williams loam (fine-loamy mixed, Typic Argiboroll) 11km north of Culbertson, MT. Plots, replicated four times in randomized blocks, were 12m×15m. Rotations were: (1) fallow, sunflower (Helianthus annuus L.), barley (Hordeum vulgare L), winter wheat; (2) fallow, safflower (Carthamus tinctorious L.), barley, winter wheat; (3) fallow, buckwheat (Fagopyrum esculentum Moench.), annual legume/grain forage crop, spring wheat; (4) fallow, buckwheat, annual legume/grain forage crop, winter wheat; (5) fallow, spring wheat; (6) continuous spring wheat. Soil water to 1.8m depth was determined near time of seeding and of harvest by neutron attenuation. The soil reached an upper drained limit of 0.20–0.25m3m−3 water in a 1.8m profile, equating to no more than 450m water. Safflower and sunflower used ca. 500mm water, more water than any of the other crops used. The greatest growing season water use efficiency was captured by the annual forage crop. Except following safflower and sunflower, soil water every spring was near the upper drained limit. Deep rooted crops can have a place in rotations on the semiarid northern Great Plains. But one must be prepared for variable yields and potential reduced yields following deep rooted crops, and for an occasional crop failure. Crop and soil management for alternative crops differ from that of small grain management, requiring some adaptation of management practices.

An estimate of soil mineralizable N is needed to determine crop needs for N fertilizer. The objective of this research was to estimate soil net N mineralization in soils maintained in continuous corn (Zea mays L.) (CC), corn–soybean [Glycine max (L.) Merr.] (CS), and corn–soybean–wheat (Triticum aestivum L.)/alfalfa (Medicago sativa L.)–alfalfa (CSWA) rotations that have been managed since 1990 with zero N (0N), low N (LN), and high N (HN) fertilization. Soil samples were taken from 0‐ to 20‐cm depth in plots planted to corn in 1998. In order to produce more realistic time‐series data of net N mineralization, soils were incubated in filtration units in a variable‐temperature incubator (VTI) that mimicked field soil temperatures under a growing corn canopy. Rotation and N fertilization significantly affected net N mineralization in soil samples. Cumulative net N mineralized in a 189‐d field temperature incubation averaged 133 ± 6 kg ha−1 in CC, 142 ± 5 kg ha−1 in CS, and 189 ± 5 kg ha−1 in CSWA. Across rotations, average net N mineralized was 166 ± 9 kg ha−1 in 0N plots, 147 ± 10 kg ha−1 in LN plots, and 152 ± 10 kg ha−1 in HN plots. Inclusion of a legume, particularly alfalfa, in the rotation increased net N mineralized. Generally, more net N was mineralized from plots receiving no fertilizer N than from soil with a history of N fertilization. Variable‐temperature incubation produced realistic time‐series data with low sample variability.