Irrigated Corn Yield and Nitrogen Accumulation ... - PubAg - USDA

Irrigated Corn Yield and Nitrogen Accumulation Response in a Comparison of No-till and Conventional Till: Tillage and Surface-Residue Variables Albert L. Sims,* James S. Schepers, Robert A. Olson, and James F. Power ABSTRACT Comparisons between no-till and conventional-till management are often confounded by variation in both tillage and residue placement. The objective of this research was to separate the tillage variable from the surface-residue variable associated with no-till and conventional-till management comparisons in irrigated continuous corn (Zea mays L.) production. Two Nebraska locations (Mead and Clay Center) with differences in soil types and climate were selected. Four tillageresidue treatments [NT-NK (no-till, residue removed), NT-R (no-till, surface residue), T-NR (till, residue removed), T-R (conventional till, surface residue)] were fertilized by either broadcasting at planting or sidedressing at the 6-leaf stage with rates of 0, 56,112, and 168 kg N ha '. At Clay Center, grain yields and total N accumulation were similar for all tillage-residue treatment combinations in all years when the highest fertilizer N rate was used. In 2 of 3 yr at Mead, grain yields and total N accumulation were less for no-till than conventionaltill treatments, but in 1 yr the yields and total N accumulations were greater in no-till than conventional-till treatments. At Mead, surface residue resulted in lower grain yields and total N accumulation compared with bare soil at lower N rates, but not at greater N rates, in 2 of 3 yr. Sidedressing fertilizer N was generally a more efficient N placement than broadcasting. Differences between tillage and residue effects at Clay Center and residue effects at Mead were overcome with higher rates of fertilizer N. Tillage effects at Mead did not appear to be N-related. The data suggest that tillage may be necessary to maintain optimum production levels on finer-textured soils when A.L. Sims, Univ. of Minnesota, Northwest Exp. Stn., 2900 University Ave., Crookston, MN 56716; J.S. Schepers and J.F. Power (retired), USDA-ARS and Dep. of Agronomy, and R.A. Olson (deceased), Dep. of Agronomy, 119 Keim Hall-East Campus, Univ. of Nebraska, Lincoln, NE 68583. Minn. Agric. Exp. Stn. No. 98101008. Received 21 Jan. 1998. *Corresponding author ([email protected]). Published in Agron. J. 90:630-637 (1998).

spring soil temperatures are cool and slow to warm. When spring soil temperatures are warm, no-till strategies can be used for optimum production levels on these soils.

N

O-TILL PRODUCTION STRATEGIES are used on about 7% of the cropland in the U.S. Corn Belt, compared with 39% for all other conservation tillage strategies (Lal et al., 1994). Six percent of the corn production in Nebraska is grown with no-till strategies, compared with 54% with conventional tillage that does not include the moldboard plow (i.e., multiple disking, chisel plows, etc.) (Allmaras et al., 1994). In addition, 60% of the approximate 2.8 million hectares of irrigated corn in Nebraska is irrigated with sprinkler systems (Allmaras et al., 1994). While no-till management would be difficult with furrow irrigation systems, it may be a viable management strategy with sprinkler irrigation, especially center-pivot systems. The confounding factors of both tillage and previous crop residue placement are inherent in any comparison of no-till and conventional-till management. Tillage effects on corn production may be more complex than simply a means by which residue can be manipulated. Van Doren and Triplett (1965, 1973) reported that inherent properties of individual soils could alter the effects of tillage method and residue placement. They reported that tillage may be necessary on light-colored, Abbreviations: ODD, growing degree days; NT-NR, no-till, residue removed; NT-R, no-till, surface residue; T-NR, conventional till, residue removed; T-R, conventional till, surface residue.

SIMS ET AL.:

EVALUATION OF TILLAGE

AND SURFACE RESIDUE

poorly structured soils, but may not be necessary on dark-colored soils with good structural stability. The maintenance of previous crop residue on the soil surface is associated with reduced soil erosion (Borst and Mederski, 1957; Hays, 1961) and soil temperatures (Burrows and Larson, 1962; Wilhelm et al., 1986) and increased soil water content (Blevins et al., 1971; Hill and Blevins, 1973;Wilhelmet al., 1986), relative to bare soil surfaces. In addition to effects on soil physical properties, tillage and residue placement can have strong effects on soil microbial populations and distributions (Doran, 1980), which in turn can have a major impact on soil N dynamics and availability. There are numerous reports comparing the effects of no-till practices with conventional and reduced tillage practices for corn production. Muchof this effort has been focused in the U.S. Corn Belt and eastward. Generally, corn production using no-till practices has compared favorably with production resulting from conventional or reduced tillage practices. Corn yields from no-till have been reported as similar to or exceeding yields from conventional tillage on well-drained soils when optimumrates of fertilizer N are used (Bandel et al., 1975; Moschler and Martens, 1975; Van Doren et al., 1976; Blevins et al., 1980; Meisinger et al., 1985). At suboptimal fertilizer N rates, yields were generally greater in conventional-till as compared with no-till management. No-till management frequently required higher fertilizer N rates to obtain maximum yields; however, maximumno-till yields were greater than maximumconventional-till yields (Legg et al., 1979; Meisinger et al., 1985; Evanylo, 1990). On poorly drained soils, especially during years of normal or above-normal precipitation, corn yields have generally been less in notill than conventional-till managementwhen continuous corn was grown, regardless of rate of fertilizer N (Griffith et al., 1973; Van Doren et al., 1976; Dick and Van Doren, 1985). These findings emphasize not only that fertilizer N managementcan vary between no-till and conventional-till management,but also that nonfertilizer N factors, such as soil and weather conditions, can significantly affect corn production in no-till systems. This research project was designed to separate the tillage variable from the surface-residue variable associated with no-till and conventional-till managementcomparisons in irrigated continuous corn production. Specific objectives were to compare corn grain yield and total N accumulation responses in tilled and nontilled soil with surface residue or with previous crop residue removed,and to evaluate the effects of fertilizer N management on these responses. Major emphasis was placed on preplant tillage management. Though not an experimental variable, irrigation was used to reduce the soil moisture differences that are frequently observed between the two managementstrategies. MATERIALS AND METHODS Field experimentswere conductedat two locations in Nebraska that represent different climatic zonesand soil types. The soil type at the University of NebraskaField Laboratory at Meadwas a Sharpsburgsilty clay loam (fine, smectitic, mesicTypicArgiudoll); Thesoil at the SouthCentral Research

VARIABLES IN CORN MANAGEMENT

631

and EducationCenter at Clay Center was a Hastings silt loam (fine, smectitic, mesic Udic Argiustoll). The experimentwas conductedfor 5 yr at bothlocations, with each treatmentbeing applied to the sameplot every year. The first 2 yr are not discussed, so that analysis and interpretation can be applied to moreestablished tillage strategies and soil environments. Datareported here weretaken fromthe last 3 yr of the experiment, identified as Year 3, Year 4, and Year5. Experimentaldesign was a split-split plot, randomizedcomplete block design with four replications at each site. Wholeplot dimensionswere 24.4 by 9.1 mand treatments were combinations of tillage and residue management: NT-NR, no-till, residue removed;NT-R,no-till, surface residue; T-NR,conventional till, residue removed;T-R, conventional till, surface residue. Residueon all plots wasshredded,leaving a 2- to 3-cmstubble at the soil surface. Residuewas removed by hand-raking treatments NT-NR,T-NR,and T-R prior to tillage operations. Residue replaced on treatment T-R was equivalent to the residue removedfrom that treatment (=2-3 Mgha-I yr-1) and was replaced after planting. Tillage consisted of twopasses with a tandemdisk in opposite directions to a depth of 10 to 12 cm. It was assumedthat residue levels were generally equivalent across the entire wholeplot, due to wind, overwintering,and shreddingoperations. Fourfertilizer N rates (0, 56, 112, and 168 kg N ha-~) were applied to split plots within each whole plot, with the N supplied as NH4NO3 (34-0-0 N-P-K). Each split plot was subdivided and split-split plot treatmentsconsistedof either broadcastapplication of fertilizer N at planting or sidedress application at approximately the 6-leaf stage. Broadcastfertilizer application was done by evenly hand-spreading the fertilizer over the soil surfaceafter planting. Sidedressfertilizer applicationwas accomplishedby hand-digginga trench about 5 to 7 cmdeep, 15 cmawayfrom each row, evenly distributing the fertilizer in the trench, then buryingthe fertilizer using the soil removed duringthe trenchingoperation. Split-plot dimensionswere6.1 by 9.1 mand split-split plot dimensionswere 6.1 by 4.6 m. Residue shredding and removal and tillage operations were completed2 to 4 d prior to planting except at ClayCenter in Year 4, whenrain delayed planting for 2 wk. Residue was returned to the T-Rtreatments at 2 to 5 d after planting by evenly spreading the residue over the entire plot area, then carefully pushingaside the residue that wasdirectly over the seed row. Broadcastapplication of fertilizer N wascompleted immediatelyafter residue was replaced. Cornwas planted in 0.76-m-widerows (6 rows per splitsplit plot) with a planter designedfor no-till conditions. Soil disturbance by the planter was 10 cm wide and 5 cm deep. + 4000 at Corn at the Meadlocation was planted 27 May(NC 68 000 seeds ha-l), 17 May(NC+ 4710at 89 000 seeds ha-l), and 17 May(Pioneer 3377at 71 000 seeds ha-1) in Years 3, 4, and 5, respectively. Cornat the Clay Center location was ++ planted 16 May(NC 4710at 71 000 seeds ha-X), 8 June (NC 1341at 89 000 seeds ha-l), and 21 May(Pioneer3377at 71 000 seeds ha-1) in the samerespectiv~ years. Appropriateinsecticides and herbicides were applied with either the planter or immediatelyafter planting to control insect pests and weeds. Additional herbicides combinedwith manual methodswere applied during the growingseason to control weeds. In-season insecticides wereapplied in Year4 to control corn borer. Both locations were irrigated as neededwith solid set sprinkler systems. Plants were harvested from 6 m of two center rows from eachsplit-split plot after physiologicalmaturityandwereseparated into ears and stover. Grain was shelled, weighed,and subsampled.Subsampleswere weighed,dried at 65°Cuntil no further weight reduction occurred, weighed, and groundto a fine powder.Stover sampleswere weighed, processed through a silage chopper, and subsampled. Stover subsampleswere

632

AGRONOMY JOURNAL, VOL. 90,

weighed,dried at 65°Cuntil no further weight reduction occurred, weighed, and ground in a Wiley mill with a 2-mm screen. Subsamplesof both grain and stover were digested in a salicylic acid-thiosulfate modifiedmicro-Kjeldahldigestion process (Bremnerand Mulvaney,1982); the resulting digest was analyzed for total N concentration using automated wet chemistry procedures. Total N accumulationwas calculated from grain and stover dry matter production multiplied by the respective Nconcentration. Grain yields were calculated -1. by adjusting grain dry matter production to 155 g H20 kg Statistical analysis was completedusing a general linear modelin SAS(Statistical AnalysisSystem)(SASInst., 1987). Single degree of freedomorthogonal contrasts were used to analyzetillage and residue treatments, fertilizer Nrates, and their interactions with and without fertilizer N application methods. Control treatments (0 N rate) were analyzed separately fromtreatments receiving fertilizer N. Single degreeof freedomorthogonal contrasts were used to analyze control plots and whole-plottreatmentswherefertilizer N wasapplied. Significance was determined at the P ~ 0.05 level. In some cases, the sumsof squares of individual contrasts were compared against the maintreatment effects sumsof squares, to identify the contrast that accountedfor the greatest amount of variation in maintreatmenteffects (Little, 1981). Fisher’s LSDwas used to comparefertilizer application methodswithin tillage-residue treatment combinations,due to significant interactions betweenfertilizer methodsand tillage-residue treatments (Gomezand Gomez,1984). Weatherdata (temperature and precipitation) were collected from weather stations located within i kmof each of the two experimental sites. Growingdegree days (GDD)were determinedaccordingto Neild and Dreier (1975). Soil temperatures weremonitorednear the weatherstation on a bare soil surface at a 10-cmdepth.

SEPTEMBER-OCTOBER 1998

between locations during the course of this experiment, but there were some similarities (Table 1). Relative responses to tillage and residue treatment were influenced by the application of fertilizer N. Control-plot (0 fertilizer N) grain yield and total accumulation was less in no-till than in conventionaltill treatments at Meadin Year 3 (Table la). By contrast, the conventional-till treatments reduced yields and total N accumulation at the Clay Center site. Variation due to tillage treatment contributed 81 to 92%and 93 to 96% of the total variation in main tillage-residue treatment effects on grain yields and total N accumulation, respectively, at both locations (Table 2). In Years 4 and 5, most of the Meadcontrol-plot variation in grain yield and total N accumulation response to main treatment effects was due to residue treatment (Table 2). Residue treatments accounted for 83 and 74%of grain yield variation and 81 and 64% of total N accumulation variation in Years 4 and 5, respectively (Table 2); however, residue treatments had opposite effects between the 2 yr. Comparedwith where residue was removed, surface residue significantly suppressed grain yields in Year 4, but increased yields in Year 5 (Table la). These same trends occurred in total accumulation response to residue treatment, although they were not significant in Year 4. There were no significant effects of either tillage or residue treatment on grain yield or total N accumulation at the Clay Center control plots in either Year 4 or 5 (Table la). Nevertheless, comparisons of the variation due to main treatment effects and single degree of freedomorthogonal contrasts of tillage and residue treatment comparisons reveal that tillage accounted for 83 and 79% of the variation in grain yield and total N accumulation, respectively, in Year 5 (Table 2). Grain yields and total N accumulation were increased when fertilizer N was applied (Table la and lb). This

RESULTS AND DISCUSSION Tillage and Residue Treatment Effects Grain yield and total N accumulation response to tillage and residue treatment varied amongyears and

Table 1. Corngrain yields and total N accumulation response to tillage-residue treatment combinations in control plots (0 N ha-a) and in fertilized plots (averaged over all fertilizer N rates and methodsof application) in yrs 3, 4, and 5 at two locations in Nebraska. Mead

Clay Center

Grainyield Treatment

Yr 3 --

Yr 4 Mg

ha -~

N accumulation Yr 5 --

Yr 3

Yr 5

--kgha

Yr 4 -t-

69.1 111.9 71.9 83.2

Yr 3

Yr 4

--Mgha Control(0 fertilizer N applied)

NT-NR NT-R T-NR T-R Contrasts T vs. NT R vs. NR T × R

1.9 1.9 4.2 3.0

3.1 2.1 3.5 2.6

3.9 6.5 3.8 4.9

35.3 40.8 63.1 59.0

46.7 43.9 48.4 45.1

** NS NS

NS ** NS

NS ** NS

** NS NS

NS NS NS

NT-NR NT-R T-NR T-R

5.0 4.0 6.4 7.2

6.1 5.0 7.3 7.2

9.6 10.0 9.0 8.8

94.9 86.9 112.5 126.5

100.2 88.6 107.5 105.1

Contrasts T vs. NT R vs. NR T× R

*** NS *

*** * *

* NS NS

*** NS **

** * NS

N accumulation

Grainyield

3.8 3.9 2.4 1.6

NS ** ** NS NS NS Fe~ilizerN applied 158.0 7.0 167.4 7.0 145.8 6.0 149.1 4.7

Yr 5

Yr 3

-~-

Yr 4

--kgha

Yr 5 ~--

4.0 3.2 3.8 3.6

4.0 4.1 4.3 4.5

58.9 64.7 43.9 38.9

52.6 47.4 54.0 54.4

58.5 67.9 75.1 78.1

NS NS NS

NS NS NS

* NS NS

NS NS NS

NS NS NS

7.4 7.6 7.3 6.8

8.8 8.7 9.0 8.8

126.6 130.6 121.5 94.5

109.4 112.6 108.3 106.5

145.9 147.5 142.5 145.6

* *** ** NS *** NS NS NS ** NS NS * NS NS NS ** NS NS ** NS NS *,**,***Significantat the 0.05, 0.01, and0.001 probabilitylevels, respectively. "~ NT-NR,NT-R,T-NR,and T-Rrepresent no-till, residue removed;no-till, surface residue; till-residue removed;andtill-surface residue; respectively.

SIMS ET AL.: EVALUATIONOF TILLAGE AND SURFACERESIDUE VARIABLESIN CORNMANAGEMENT

633

Table 2. Relative variation (% of main effect variation) of whole-plot main treatment effects on corn grain yield and total N accumulation due to tillage, residue, and their interaction variation. Relative variation Mead Grainyield Contrast

Yr 3

Yr 4

Clay Center Total N accumulation

Yr 5

Yr 3

Yr 4

Yr 5

Total N accumulation

Grainyield Yr 3

Yr 4

Yr 5

Yr 3

Yr 4

Yr 5

5 67 28

83 12 5

93 0 7

57 18 25

79 17 4

65 8 27

63 32 5

53 17 30

66 3 31

52 43 5

%of maineffect variation Control(0 fertilizer Napplied) T vs. NT R vs. NR T× R

81 8 11

17 83 0

15 74 1

96 0 4

19 81 0

T vs. NT R vs. NR T× R

86 1 13

82 10 8

90 1 9

86 1 13

67 23 10

14 92 64 3 22 5 Fertilizer Napplied 83 52 14 25 3 23

~" T, NT,R, andNRrepresenttill, no-till, residue, andno-residue,respectively. T × R represents the interaction betweentillage and residue treatments.

increase indicates that plant-available N was limiting in control plots. Values in Table lb represent the response to tillage-residue treatment combinations and were averaged over all fertilizer N rates and application methods. Significant grain yield variation due to tillage x residue treatment interactions occurred in both locations in Year 3 and at Meadin Year 4 (Table lb). This interaction was also significant for total N accumulationvariation in Year 3 at both locations (Table lb). Interactions were caused by treatment NT-R at Meadand treatment T-R at Clay Center, producing the least grain yield and accumulating the least total N compared with the other three tillage-residue treatment combinations (Table lb). Tillage effects on grain yields werehighly significant in all years at Meadand Years 3 and 4 at Clay Center comparedwith either residue effects or tillage × residue interactions (Table lb). The same occurred in tillage effects on total N accumulation in all years at Meadand Year 3 at Clay Center. Variation in grain yield and total N accumulation due to tillage treatment effects accounted for 82 to 90%and 67 to 86%, respectively, of the total variation due to main treatment effects at Meadover the 3 yr (Table 2). Variation due to residue treatment effects accounted for 1 to 23%of variation due to main treatment effects on both measured variables. Variation in grain yield and total N accumulation due to tillage treatment effects was less (52-66%) and variation due to residue effects was greater (3-43%) Clay Center than at with Mead(Table 2). Vyn and Raimbault (1993) reported generally lesser corn yields in no-tillage than in tillage, whether moldboard plow or chisel plow, over a 15-yr period in Ontario. This difference was further exaggerated when spring temperatures were below normal and soil was slow to warm. Our data suggest that tillage system had a greater effect on grain yield and total N accumulation than surface residue when fertilizer N was applied. At Mead, greater grain yields and total N accumulation occurred with conventional tillage than with no-till in Years 3 and 4, but the reverse occurred in Year 5. Commonclimatic factors in Years 3 and 4 were cool soil temperatures at planting and slow soil warmingand accumulation of GDDsduring the early part of the

growing season (Fig. 1). By contrast, Year 5 had warmer soil temperatures and rapid soil warmingand accumulation of GDDsearly in the growing season (Fig. 1). These same climatic conditions occurred at the Clay Center site, but the impact of tillage methodwas substantially less than at Mead. Staley and Perry (1995) speculated that both edaphic and climatic factors may preclude generalization of tillage effects on yields and N uptake in similar soil types. Soils at both locations were developed as Mollisols with argillic horizons from loess parent material with moderate to moderately slow permeability (Elder, 1969). Major differences between the two soils are their surface soil texture (silt loam at Clay Center and silty clay loam at Mead) and the moisture regime in which they were developed. The Hastings silt loam at Clay Center was developed under a drier environment than the Sharpsburg silty clay loam at Mead. Fertilizer N Management: N rates Highly significant grain yield and total N accumulation responses to fertilizer N rates were measuredin all years at both locations (Table 3). Significant interactions between grain yield response to N rate and residue treatment were measured in all 3 yr at Mead(Table 3). Interactions were significant between grain yield response to N rate and residue and tillage treatments only in Year 3 at Clay Center (Table 3) Grain yields tended to increase with increasing fertilizer N rates, at least to 112 kg N ha-1, in all years at both locations (Fig. 2). The exception was no-till treatments and no-residue treatments at Meadin Year 3, where yields reached their maximumat the 56 kg N ha-1 rate. In both cases, yield increases above controlplot yields (Table la) were between 2.1 and 2.5 Mg-1. Rainfall was less than normal throughout the growing season at both locations (Fig. 1). Rainfall deviation from normal was greatest at the Mead site, and may have reduced overall yield potential. Irrigation was supplied at both locations to reduce drought stress, but leaf wilting and drought symptomswere observed at Meadprior to tassel emergence and into the reproductive growth period, probably due to severe drought conditions and high air temperatures. At Mead, grain yield response to fertilizer N within

634


Year 3 ....

Year 4 -- -- Year 5 -- Long Term Average

Accumulated Precipitation 8O0 (a) 600 L:,,,j~ ¯ 400

200

GrowingDegreeDays

~_ a~-/’

400

250 5-

rsot

~’

500-I 250| ~

~’’:’:"....

252015-

/~/../..-"

500

]

Soil Temperature

/.

_ (a) 750 4

......

600 200


w20-15 50-

( t

120 ~40 ~60 180 150 250 350 150 250 50 350 CalendarDay CalendarDay CalendarDay Fig. 1. Accumulated precipitation, early-season growing degree days (GDD), and soil temperatures during the growing season of Years 3, 4, and 5 comparedwith the long-term averages at (a) Mead and (b) Clay Center, 50

tillage treatment comparisons averaged across residue treatments and residue treatment comparisons averaged across tillage methods indicate that fertilizer N rates modified residue treatment effects, but not tillage treatment effects (Fig. 2). Grain yield differences between no-till and conventional-till treatments were similar at all N rates except in Year 4, whenthere was a significant interaction betweenresponse to N rate and tillage treatment (Fig. 2; Table 3). Grain yield differences between -~ residue and no-residue treatments at the 56 kg N ha rate were not apparent when higher rates of fertilizer N were applied (Fig. 2). Interactions between grain yield response to N rate and residue treatment were significant in all years (Table 3). Although these responses fertilizer rates occurredin all years, the relative response to both tillage treatment and residue treatment was reversed in Year 5 compared with Years 3 and 4. As with grain yields, differences in total N accumulation that occurred betweenno-till and conventional-till treatments tended to remain similar at all fertilizer N rates, except in Year 4 (Fig. 3). In Year 4, differences in total N accumulation increased with increasing N rates. This

interaction between N accumulation response to N rates and tillage was significant (Table 3). Differences in total N accumulation between residue treatments tended to be smaller than betweentillage treatments at the greater fertilizer N rates (Fig. 3). In Year 5, there was no significant difference in total N accumulation between residue treatments (Table 3). At Clay Center, grain yields tended to reach a maximumat the 112 kg N ha-1 fertilizer rate in no-till and noresidue treatments in Year 3 (Fig. 2). Maximum yields conventional-till and surface-residue treatments were not as great as those measured in no-till and no-residue treatments at even the highest fertilizer N rate (Fig. 2). Yields in the conventional-till treatments and surfaceresidue treatments tended to respond linearly to increasing fertilizer N rates, indicating that higher rates of fertilizer N may have increased grain yields in these treatments to the same level as in no-till and no-residue treatments. In Years 4 and 5, there were no significant interactions in grain yield response to N rate and either tillage or residue treatment (Table 3). Grain yield differences within the tillage treatments and within the rest-

Table 3. Statistical analysis, including orthogonal contrast, of corn grain yield and total N accumulation response to tillage-residue treatment combinations, applied fertilizer N rates and application methods for three years at two locations in Nebraska. Mead

Clay Center

Grainyield

N accumulation

N accumulation

Grain yield

Sourceof variationS"

Yr 3

Yr 4

Yr 5

Yr 3

Yr 4

Yr 5

Yr 3

Yr 4

Yr 5

Yr 3

Yr 4

Yr 5

Linear (L) Quadratic (Q) Treatment × N Rate Tx L T × Q R × L R × Q N App Treatment x N App T × R × N App N Rate X N App L X N App Q x N App

* 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 * NS * NS * NS NS NS * NS **

*** NS NS NS NS NS NS *** NS NS * NS *


*,**,***Significantat the 0.05, 0.01, and 0.001 probability levels, respectively. ? T, conventional tillage; NT, no till; R, residue; NR,no residue; N App,N broadcast vs. N sidedress.

SIMS ET AL.:

635

EVALUATIONOF TILLAGE AND SURFACE RESIDUE VARIABLESIN CORN MANAGEMENT

Mead

Mead

ClayCenter 160

~Yr3

Clay Center ~

,, Yr4

t-o

-/~i

~oo 56

112

168 56

112

168

-1) Nitrogen Rate (kg ha

56

112 112 168 56 "1) Nitrogen Rate(kg ha

168

Fig. 2. Corngrain yield response to fertilizer N rates for comparisons of no-till (solid circles) vs. conventional-till (open circles) andfor no-residue (open squares) vs. residue (solid squares) over 3 yr at Mead and Clay Center, NE. Error bars represent the standard error of each mean.

Fig. 3. Total N accumulationresponseto fertilizer N rates for comparisons of no-till (solid circles) vs. conventional-till (opencircles) and for no-residue (open squares) vs. residue (solid squares) over yr at Meadand Clay Center, NE. Error bars represent the standard error of each mean.

due treatments were small at all fertilizer N rates (Fig. 2). Differences that did occur at the 56 kg N ha-~ rate were not as apparent at greater fertilizer N rates. A linear response of grain yields to fertilizer N rates was highly significant with no interactions with either tillage or residue treatment (Table 3). Significant interactions in total N accumulationresponse to tillage, residue, and fertilizer N rate treatments occurred in Year 3 at Clay Center (Table 3). As with grain yields, no-till and noresidue treatments tended to maximize total N accumulation at the 112 kg N ha-1 rate, and conventional-till and surface-residue treatments increased total N accumulation at all fertilizer N rates (Fig. 3). However,total N accumulation in the till and surface-residue treatments at 168 kg N ha-~ was similar to (only slightly lower than) no-till and no-residue treatments at 112 kg N ha-L There was no difference among the tillage and residue treatments in Years 4 and 5 (Table 3 and Fig. 3). The linear response of both grain yields and total accumulation to the range of fertilizer N rates indicate that a higher rate of fertilizer should have been included at Clay Center. Bandel and Fox (1984) reported, after summarizing 40 N rate x tillage trials, that suboptimalrates of fertilizer N are likely to result in greater grain yields in conventional-till systems than no-till systems. At optimal N rates, no-till systems would have greater yields than conventional-till systems; however, optimal N rates in no-till systems wouldbe greater than optimal N rates in conventional-till systems, due to greater yield poten-

tial in no-till systems. This greater yield potential in notill systems has been attributed to greater soil moisture content relative to conventional-till systems. In our experiment, irrigation was used to minimize the soil moisture differences often observed between the two tillage systems. Soil moisture was not measured during the course of this experiment, but it is assumedto be similar among all treatments. Exceptions may have occurred during the very early part of the growing season, when tillage and residue removal may have allowed the soil to dry and warmmore quickly than in untilled soil. Our data do not indicate that no-till has a higher yield potential than tilled systems under irrigation; however, the data do indicate that available N is influenced by surface residue in the finer-textured soils at the Mead site. In the silt loam soils at the Clay Center site, both tillage methodand surface residue appear to potentially influence available N. Differences in grain yields and total N accumulation at lower fertilizer N rates were overcomewith greater fertilizer N rates. Generally, the tillage effects at Meaddo not appear to be related to available N, evidenced by the lack of a differential response between tillage systems with increasing N rates, except in Year 4. No-till yields and total N accumulation were suppressed compared with tilled treatments in Years 3 and 4, but the reverse occurred in Year 5, indicating that soil temperature conditions at planting and within several days after planting maybe the major tillage effect in finer-textured soils. During cool springs with slow soil warming, tillage may

636



Table 4. Corn grain yield response to broadcast (BD) and sidedressed (SD) fertilizer application methods for all tillageresidue treatment combinations averaged across all fertilizer N rates at Mead and Clay Center, NE.f

Broadcast o Year ¯ Year Sidedress

,80t Mead

Grainyield Yr 3 Treatment~

BD

160 q

Yr 4 SD

Yr 5

BD SD -~ Mg ha

BD

140 ~

SD

120 J

Mead NT-NR NT-R T-NR T-R Average LSD(0.05)§

4.7 3.5 5.7 7.0 5.2

NT-NR NT-R T-NR T-R Average LSD(0.05)§

6.7 6.8 6.5 4.6 6.2

5.4 4.5 7.2 7.4 6.1 0.6 7.3 7.2 6.7 4.7 6.5 NS

5.3 4.4 6.8 6.8 5.8

100 6.9 5.5 7.8 7.7 7.0

1.0 Clay Center 7.1 7.8 7.3 7.9 7.2 7.3 6.5 7.2 7.0 7.6 NS

9.8 10.4 9.2 8.9 9.6

9.5 9.7 8.9 8.8 9.2 NS

8.8 8.6 8.9 9.1 8.9

8O E

60 180

~- Clay Center

O ~

8.8 8.9 9.0 8.6 8.8

&

~6o~

.~

140

.~f~"

_

NS

BDand SDrepresentbroadcastandsidedress fertilizer application methods, respectively. NT-NR,NT-R, T-NR, and T-R represent no-till, residue removed;notill, surfaceresidue;till-residue removed; andfill-surface residue;respectively. LSD(0.05) are for comparisons of fertilizer N applicationmethodswithin tillage-residue treatmentcombinations due to significant N application× tillage-residue treatment interactions (Gomezand Gomez,1984).

have increased the rate of soil warming compared with no-till, creating a more favorable environment for plant development. Whensoils are warmer, as in Year 5, the advantage of tillage observed in the previous 2 yr was not apparent. Under warmer conditions, no-till systems mayhave a greater yield potential as suggested by Bandel and Fox (1984), but that cannot be discerned from our data. Fertilizer N Management: Application Methods Grain yields were significantly affected by fertilizer application method in Years 3 and 4 at Mead, but not in Year 5 (Table 3). Yields were greater whenfertilizer N was sidedress-applied than when broadcast in Years 3 and 4 (Table 4a). A significant interaction among tillage, residue, and fertilizer application methodtreatments (Table 3) was due to relatively small differences bet~veen sidedress and broadcast application methods in treatments NT-NR(0.7 Mgha -1) and T-R (0.4 Mg ha -1) -1) compared with treatments NT-R (1.0 Mg ha and T-NR(1.5 Mgha-1) (Table 4a). There was no grain yield difference between fertilizer application methods in Year 5 at Meador in any year at Clay Center (Tables 3, 4a, and 4b). Total N accumulation response to fertilizer application methods was significant in Years 3 and 4 at both locations, but not in Year 5 at either location (Table 3). Interactions amongtillage, residue, and fertilizer application methods were significant at Meadin Year 3, due to greater total N accumulation in treatment NT-Rwith sidedress-applied fertilizer than occurred in any other tillage-residue treatment combination (data not shown). Interactions in total N accumulation between fertilizer

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112 168 "1) Nitrogen Rate (kg ha Fig. 4. Total Naccumulationresponseto fertilizer N rates and application methodsacross all tillage-residue treatment combinationsfor 3 yr at Meadand Clay Center, NE. Error bars represent the standard error of each mean.

application methodand fertilizer N rate were significant at both locations in Years 3 and 4 (Table 3). Generally, greater N rates were required when broadcast than when sidedress-applied to achieve similar amounts of total N accumulation (Fig. 4). The exception was Meadin Year 4, where total N accumulation was greater whenfertilizer N was sidedress-applied at all N rates. In Year 5, measured total N accumulation was almost identical with both N application methodsat all N rates at both locations (Fig. 4). Differences between broadcast and sidedressoapplied fertilizer N effects on grain yields and total N accumulation indicate greater N availability when N was sidedress-applied in Years 3 and 4, especially at Mead. This was not the case in Year 5. Net N immobilization may occur early in the growing season, but net N mineralization can occur later in the growing season (Smith and Douglas, 1971). The time of year when net N mineralization occurs depends on the rate and degree of residue or organic matter decomposition. Fertilizer N placed in contact with surface residue early in the growingseason, as was done with the broadcast application, may have been subject to greater immobilization, denitrification during wet periods, or leaching compared with sidedressed fertilizer N. Sidedressed fertilizer N was placed below soil surface residue at approximately the time when crop demand for N was beginning to increase rapidly. Warmspring temperatures in Year 5 (Fig. 1) may have stimulated greater N mineralization early enough in the growing season that N availability was not greatly different between the two application meth-

SIMS ET AL.: EVALUATION OF TILLAGE AND SURFACE RESIDUE VARIABLES IN CORN MANAGEMENT

ods. In contrast, spring temperatures in Years 3 and 4 were cooler and may have delayed net N mineralization until later in the growing season. Mengel et al. (1982) reported greater grain yields and ear leaf N concentrations when fertilizer N was placed below the soil surface compared with surface applications, especially in notill systems. The authors attributed this difference to greater potential for N volatilization and immobilization with surface applications.

CONCLUSIONS The results of this experiment suggest that no-till corn production could be a viable management strategy in drier climates with irrigation and silt loam soils. Increasing fertilizer N rate applications minimized potential yield reductions associated with implementing no-till corn production. In more humid environments and with finer-textured soils, potential yield reductions with surface residue appear to be minimized with fertilizer N management, but tillage effects appear to be independent of N management. Comparisons of the tillage effects on corn production with soil temperature data obtained from weather stations within close proximity of each experimental site may indicate that tillage effects are related to cool spring soil temperatures. Our data suggest that preplant tillage should be performed to obtain optimum corn grain yield potential during years when spring soil temperatures are cool, especially in finer-textured soils. When spring soil temperatures are warm, however, tillage may not be necessary to achieve optimum yield potential. It is likely that soil temperature and moisture are related more closely with soil loosening and disturbance, as through tillage, with the soil types at Mead than with soil types at Clay Center, and that this relationship involves more than soil N dynamics.

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