Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol52.Issue1-2.Sept1999:

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Impacts of tillage and no-till on production of maize

and soybean on an eroded Illinois silt loam soil

I. Hussain

a

, K.R. Olson

b,*

, S. A. Ebelhar

c

a_{Mohalla Hariwalla, Pindi Gheb, Dist Attock, Pakistan}

b_{Department of Natural Resources and Environmental Sciences, W-401C Turner Hall,}

University of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801, USA

c_{Dixon Springs Agricultural Center, Simpson, IL, USA}

Received 25 May 1998; received in revised form 10 November 1998; accepted 17 May 1999

Abstract

In the United States, millions of hectares of highly erodible cropland have been in the Conservation Reserve Program (CRP) for the past 10 years. Any conversion of CRP land back to maize (Zea mays L.) and soybean (Glycine max L. Merr.) production could require the use of conservation tillage systems, such as NT and CP, to meet federal and state soil erosion control standards. Evaluations of yield response of these conservation tillage systems such as NT and CP, over time are needed to assess the return of this land to crop production. An eight-year study was conducted in southern Illinois on land similar to that being removed from CRP to evaluate the effects of conservation tillage systems on maize and soybean yields and for the maintenance and restoration of soil productivity of previously eroded soils. Soils had been in tall fescue (Festuca arundinacea

L.) sod for more than 10 years prior to the study. In 1989, no-till (NT), chisel plow (CP), and moldboard plow (MP) treatments were replicated six times in a Latin Square Design on sloping, moderately well-drained, moderately eroded phase of a Grantsburg soil (Albic Luvisol) (®ne-silty, mixed, mesic Typic Fragiudalf). Starting with maize, maize and soybean were grown in alternate years. Surface crop residue levels were higher with the NT system than with the CP and MP systems. Soil temperature at 20 cm was lower (1.18C) with NT than with the other systems in 1996. Plant-available water was slightly higher with NT and CP systems than with the MP system. In 1995, maize was taller with the NT system than with the MP and CP systems. The MP system plots had higher plant populations in 1995 and 1996, but crop yields were higher with the NT system than with the MP system. The four-year average maize yields were equal (9.81, 9.74, and 9.80 Mg haÿ1) for NT, CP, and MP systems, respectively, as a result of a signi®cantly higher yield with the MP system in the ®rst year which offset the higher yields with the NT and the CP systems during the last two years. The four-year average soybean yield with NT (2.90 Mg haÿ1_{) was 15% higher than with the MP (2.55 Mg ha}ÿ1_{) system. Crop yields for eight years (four years maize and}

Keywords:Conservation tillage; Yield; Crop growth; Soil water; Plant population

*Corresponding author: Tel.: +1-217-333-9639; fax: +1-217-244-3219

E-mail address:k-olson1@uiuc.edu (K.R. Olson)

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1. Introduction

In the United States, the Food Security Act of 1985, the 1900 and 1995 Farm bills, and the Illinois T by 2000 Program have resulted in millions of hectares of erodible land previously in row crops being put into the Conservation Reserve Program (CRP) for 10 years. Any conversion of CRP land back to maize and soybean production could require the use of conservation tillage systems, such as NT and CP, to meet soil erosion control standards. Evaluations of yield response of these conservation tillage systems over time are needed to assess returning this land to crop production.

The severity of erosion can be reduced by main-taining crop residue on the soil surface (Dickey et al., 1985; Alberts and Neibling, 1994). At planting, with chisel plowing residue cover is 30% and much higher with no-till due to a lack of, or minimum, soil dis-turbance (Lal et al., 1994). Lueschen et al. (1991), for a maize±soybean rotation in Minnesota, observed 69±82%, 49%, and 10% of soybean residue cover on the soil surface after maize planting in no-tillage, chisel plow, and moldboard plow system plots, respec-tively.

A higher surface residue cover in combination with minimum soil disturbance, affect soil water conserva-tion and soil temperature. The amount of plant-avail-able water in soil at planting time increased and the soil temperature decreased with the amount of plant residue on the soil surface at Lincoln, Nebraska (Wilhelm et al., 1986).

From the 1954±1988 data from central Iowa, plant-available soil water and heat stress during July (sum-mer) were identi®ed by Carlson (1990) as two major weather factors that affected the maize yield. At Sydney, MT, Aase and Tanaka (1987) found that residue on the soil surface reduced the early evapora-tion during summer from the upper 10 cm of soil compared with that of bare soil, but total soil-water losses during the season were not signi®cantly differ-ent. Schillinger and Bolton (1993) compared no-till, stubble mulch, and moldboard plow and found that the residue in no-till decreased the evaporation during frequent rainfall periods, but the evaporation in no-till was faster during the dry period of summer due to non-disturbed capillary ¯ow. In Garden City, Kansas, Norwood (1994) studied different crop rotations with

no-till and conventional tillage and found an addi-tional 62% of water below the 0.9-m depth in no-till due to less evaporation and no surface runoff com-pared with that of conventional tillage.

Generally, conservation tillage resulted in an increase in crop yield compared with that of a mold-board plow system. Lawrence et al. (1994) showed in a four-year study in a semi-arid environment in Aus-tralia that no-till had a higher crop yield than did reduced till fallow or conventional till fallow. A positive linear response between yields of maize and soybean, and the amount of residue applied to a no-till system was observed by Wilhelm et al. (1986). Lueschen et al. (1991), in a maize±soybean rotation in Minnesota, found an increase of 6.30 Mg haÿ1 in yield of the NT system above the MP system in a dry year. Kapusta et al. (1996) studied the effects of tillage systems for 20 years and found equal maize yield in no-till, reduced till, and conven-tional tillage despite the lower plant population in no-till.

Crop rotation in combination with different tillage systems can also affect crop yields. After 12 years of study, a maize±soybean rotation yielded 8.7 Mg haÿ1, compared with 7.7 Mg haÿ1, for continuous maize, while soybean yields were 2.6 Mg haÿ1in both rota-tions (Karlen et al., 1991). West et al. (1996) studied the effect of moldboard plow, ridge, chisel and no-till for 20 years in north-central Indiana under different rotations of continuous maize, continuous soybean, maize after soybean, and soybean after maize. No-till maize yield and plant population were reduced 14% and 8%, respectively, in continuous maize. Kapusta et al. (1996) reported greater plant height in no-till compared with that of moldboard plow, while the maize population was lower in no-till in comparison with moldboard plow. Dickey et al. (1994) in Nebraska, studied plow, chisel, disk, and no-till sys-tems on a silty clay loam soil for eight years and found the highest yield for sorghum (Sorghum biocolor(L.) Moench) and soybean under the no-till system.

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be due to lower soil organic carbon and nitrogen mineralization and higher immobilization of fertilizer nitrogen, than those of conventional tillage (House et al., 1984; Rice and Smith, 1984). Rice et al. (1986) and Kapusta et al. (1996) also reported no differences in maize yield with no-till and conventional tillage over time.

In different tillage systems, crop yields were also affected by soil drainage conditions. Some researchers reported lower yields with no-till, than conventional tillage in poorly drained soils (Dick and Van Doren, 1985) and higher yields for well drained soils (Wagger and Denton, 1992; Ismail et al., 1994).

Since limited data were available on the long-term tillage responses on sloping and eroded soils in south-ern Illinois, this project was started in 1989. Tillage effects were not profound in the early years of the study (Kitur et al., 1994). The study was continued with the objective of evaluating long-term tillage systems (no-till, chisel plow, and moldboard plow) effects on maize and soybean yields and the main-tenance and restoration of soil productivity of pre-viously eroded soils in southern Illinois.

2. Methods and materials

A tillage experiment was started on April 12, 1989, at the Dixon Springs Agricultural Research Center in southern Illinois. The soil at the study site was a moderately eroded phase of Grantsburg silt loam (Albic Luvisol) (Dudal, 1970) (®ne-silty, mixed, mesic Typic Fragiudalf) (Soil Survey Staff, 1975) with an average depth of 64 cm to a root-restricting fragipan. Grantsburg soil was formed in loess under forest vegetation and underlain at a depth of 2±5 m by siltstone. The area, with an average slope of 6%, had been in tall fescue hayland for >10 years prior to the start of this experiment. On April 12, 1989, lime (CaCO3) with 94% calcium carbonate equivalent, at the rate of 3.1, 4.9, and 7.3 Mg haÿ1, was applied on upper, middle, and lower rows of the plot area, respec-tively, to raise the soil pH of each row to the optimum level for maize and soybean production. Three tillage treatments, namely no-till (NT), chisel plow (CP), and moldboard plow (MP), were established on April 27, 1989. Starting with maize in 1989, maize and soybean were grown in alternate years. The experimental

design was a Youden Type III Incomplete Latin Square (Cochran and Cox, 1957) that allowed for randomization of the tillage treatments (NT, CP, and MP), both by row (block) and by column. This replication was used to control random variability in both directions. Each treatment was randomized six times in 18 plots with a size of 9 m12 m. The columns were separated with 6 m buffer strips of sod.

2.1. Field activities and tillage operations

The implements used in each tillage system and depth of tillage were as follows: NT (no-tillage), CP (chisel plowed to 15 cm with diskings to 5 cm), and MP (moldboard plowed to 15 cm with diskings to 5 cm). The actual type, date, and number of primary and secondary tillage operations applied to the plot area are listed in Table 1. The cultural practices used including crop, year, planting date, seeding rate, and fertilizer application rates are provided in Table 2. The weed control including the herbicide, rate and date of application are listed in Table 3.

2.2. Field measurements and sampling

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Table 1

Type, date and number of field operations on plot area at Dixon Springs, IL

Year System No-till Chisel Moldboard

date No. date No. date No.

1989 plowing Ð Ð 27 Apr 1 27 Apr 1

disking Ð Ð 27 Apr 2 27 Apr 2

disking Ð Ð 12 May 1 12 May 1

1990 plowing Ð Ð 05 Jun 1 05 Jun 1

disking Ð Ð 05 Jun 1 05 Jun 1

1991 plowing Ð Ð 03 May 1 03 May 1

1995 plowing Ð Ð 06 Apr 1 06 Apr 1

disking 31 May 1 31 May 1

1996 plowing Ð Ð 05 Jun 1 05 Jun 1

Table 2

Crop, planting date, seeding rate and fertilizer rates used in the present study Year Crop Planting

date

Seeding rate (seeds haÿ1)

N (kg haÿ1₎ _{P (kg ha}ÿ1₎ _{K (kg ha}ÿ1₎

1989 maize 12 May 64 000 212 67 116

1990 soybean 07 Jun 432 000 0 67 260

1991 maize 08 May 64 000 168 67 260

1992 soybean 22 May 432 000 0 0 0

1993 maize 17 May 64 000 184 55 232

1994 soybean 08 Jun 432 000 0 0 0

1995 maize 31 May 64 000 218 55 232

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Staff, 1995). The crop yield and plant population data from 1989 to 1996 were collected as part of this study. The soil loss rates were determined using USLE (Walker and Pope, 1983).

2.3. Statistical analysis

Statistical analysis for all parameters were per-formed using the procedures from Statistical Analysis System (SAS) computer software (SAS Institute, 1995). Analysis of variance, least-square means of selected variables, and covariance analysis using plant population (in the case of crop yield) were performed by general linear model (GLM) procedures.

3. Results and discussion

3.1. Crop residues and estimated erosion

The no-till system maintained a signi®cantly higher amount of residue on the soil surface as compared with that of the CP and MP systems during each year at planting (Table 4). Crop residue on the soil surface was higher with maize as previous crop, compared with that of soybean because of higher residue pro-duction from maize and lower rate of decomposition of maize residue (Lueschen et al., 1991) than soybean residue. On Grantsburg soil with 5±7% slopes, the estimated annual soil loss, measured with USLE, was

Table 3

Weed control practices used during the study

Year Herbicide Rate Date

1989 Glyphosate 2.34 l haÿ1 21 Apr

Atrazine 3.4 l haÿ1 12 May

Metolachlor 2.3 l haÿ1 12 May

1990 Glyphosate 2.34 l haÿ1 01 Jun

Metolachlor 2.34 l haÿ1 _{08 Jun}

Sethoxydim 1.90 l haÿ1 _{08 Jun}

Metrubuzin and Chlorimuron 0.50 kg haÿ1 _{08 Jun}

Surfactant 0.62 l 100 lÿ1 _{08 Jun}

1991 Gramoxone 2.34 l haÿ1 _{08 May}

Metolachlor 2.34 l haÿ1 _{08 May}

Atrazine 4.68 l haÿ1 _{08 May}

1992 Metolachlor 2.34 l haÿ1 22 May

Sethoxydim 1.90 l haÿ1 22 May

Metrubuzin and Chlorimuron 0.50 kg haÿ1 22 May Surfactant 0.62 l 100 lÿ1 22 May

1993 Atrazine 3.5 l haÿ1 17 May

Metolachlor 2.3 l haÿ1 17 May

Glyphosate 2.33 l haÿ1 17 May

1994 Glyphosate 2.33 l haÿ1 _{08 Jun}

Metolachlor 2.33 l haÿ1 _{08 Jun}

Metrubuzin and Chlorimuron 0.42 l haÿ1 _{08 Jun}

Surfactant 0.48 kg haÿ1 _{08 Jun}

1995 Glyphosate 2.33 l haÿ1 _{31 May}

Alachlor 2.34 l haÿ1 _{31 May}

Atrazine 4.68 l haÿ1 31 May

1996 Glyphosate 2.33 l haÿ1 05 Jun

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7.9, 21.1, and 29.5 Mg haÿ1with the NT, CP and MP systems, respectively (Table 4) (Walker and Pope, 1983). The higher the percentage of crop residue (Table 4) on the soil surface with the NT system protected the soil from erosion and kept it below the tolerance level of 8.4 Mg haÿ1yearÿ1 (Walker and Pope, 1983). On the other hand, rill erosion was observed with the MP and CP systems due, in part, to less residue on soil surface compared with that of the NT system.

3.2. Soil responses

During the 1995 growing season, differences in plant-available water due to tillage systems were non-signi®cant for all depths on all sampling dates (Table 5). The NT plots had a slightly higher

plant-available water compared with that of the CP and MP plots in the 0±15 cm and the 15±45 cm soil layers at 25 days after planting. The CP system had more plant-available water in the 45±75 cm soil layer than NT and MP systems. The amount of plant-available water was equal in the 45±75 cm layer in all tillage systems at midseason in 1995, but the CP system stored more water compared with that of the NT and MP systems in the 0±15 cm soil layer. The lower amount of plant-available water with the NT system compared with that of CP system at midseason 1995 could be the result of higher plant population with the NT and MP systems compared with that of the CP system (Table 6). Plant-available water was lower at midsea-son than 25 days after planting in all tillage systems due to higher requirements of water by plants at this stage (Table 6), more potential evaporation of water from soil due to higher temperature, and below aver-age rainfall (9.1 cm) between 25 days after planting and midseason sampling. After midseason sampling, maize received 9.0 cm of rainfall from tasseling to the harvest of the crop.

During the 1996 growing season, non-signi®cant differences between tillage systems were observed in plant-available water at all depths on all sampling dates (Table 7). The NT system plots contained more available water at planting, 25 days after plant-ing, and at midseason than did the MP system plots in the 0±15, 15±45 and 45±75 cm soil layers. At planting and 25 days after planting, plant-available water dif-ferences between tillage systems were not pronounced due to abundant rainfall (Table 8) between, and around, the sampling dates. Later in the season, there was no rainfall from August 2 to 15, which resulted in 0.03 cm3 of plant-available water per cmÿ3 of soil with the NT system, while the MP and the CP systems had 0.01 cm3of plant-available water per cmÿ3of soil

Table 4

Effect of different tillage treatments on plant residue after planting and soil loss at Dixon Springs

Tillage Residue present from previous crop (% cover)a _{Soil loss (Mg ha}ÿ1₎b

1993 1994 1995 1996

No-till 75a 95a 76a 91a 7.9c

Chisel plow 21b 47b 22b 18b 21.1b

Moldboard plow 6c 17c 6c 6c 29.5a

a_{For each year, means within the same column followed by the same letter are not significantly different at the}_p_{0.05 probability level.} b_{Soil loss is calculated by the universal soil loss equation (USLE).}

Table 5

Tillage effects on plant available water at different depths during 1995 at Dixon Springs

Tillage Plant available water (cm3of water per cmÿ3of soil)a

soil depth (cm)

0±15 15±45 45±75

Twenty-five days after planting(22 Jun 1995)

No-till 0.22a 0.20a 0.17a Chisel plow 0.19a 0.20a 0.19a Moldboard plow 0.18a 0.18a 0.16a

Midseason(26 Jul 1995)

a_{For each date, means within the same depth followed by the}

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in the 0±15 cm soil layer at midseason sampling. In the 15±45 and 45±75 cm soil layers plant-available water was also higher in the NT compared with that of the MP system. The 1996 soybean crop received suf®cient rainfall from June 26 (25 days after planting) to August 15 (midseason), but rainfall during August was below average. Plant-available water was lower at

midseason compared with that at earlier dates in the 0± 15, 15±45 and 45±75 cm soil layers due to the high water requirement of the crop at midseason. Although the amount of available water was low in the 0±15 and 15±45 cm soil layers at midseason in all tillage sys-tems, rainfall of 16.3 cm to the end of September provided enough plant-available water for later stages of soybean growth. The availability of slightly more water with the NT system compared with that of the CP and the MP systems could be attributed to the suppression of evaporation, more in®ltration, and lower runoff which resulted in more water conserva-tion due to the presence of more residue on the soil surface (Table 4). The eroded Grantsburg soils can store 15 cm of water in the 75 cm of soil (Table 4) above a root-restricting fragipan. Maize needs 100 cm of water from storage and re-charge by rain for optimum production (Troeh et al., 1980).

Soil temperatures (average daytime temperatures) were recorded at 25 days after planting of the crop in 1995 and 1996. During both years, the MP and CP systems had a higher soil temperature compared with that of the NT system. In 1995, the differences in soil temperature were non-signi®cant between tillage treatments, while the differences were signi®cant in 1996 (Table 9). The lower NT temperatures in 1995 and 1996 were probably due to the presence of more water and higher amount of residue on the soil surface (Table 9). The differences in soil temperature were signi®cant (p0.05) in 1996 probably due to the higher amount of residue on soil surface by a

preced-Table 6

Effect of different tillage treatments on the maize and soybean population during 1989±1996 at Dixon Springs Tillage Plant population (plants haÿ1)a

1989 1991 1993 1995 Averageb

Maize

No-till 55 300 57 900 51 400 58 800 55 800

Chisel plow 59 200ab 47 400b 54 100a 55 700b 54 100b Moldboard plow 62 900a 52 200ab 52 600a 62 200a 57 500a

1990 1992 1994 1996 Averageb

Soybean

No-till 191 000b 344 000a 303 000a 263 000b 276 000a Chisel plow 247 000a 335 000a 229 000b 277 000b 272 000a Moldboard plow 249 000a 343 000a 181 000c 309 000a 270 000a

a_{For each crop, means within the same year followed by the same letter are not significantly different at the}_p

0.05 probability level.

b_{Four-year average.}

Table 7

Tillage effects on plant available water at different depths during 1996 at Dixon Springs

Tillage Plant available water (cm3_{of water}

per cmÿ3of soil)a

soil depth (cm)

0±15 15±45 45±75

At planting(6 Jun 1996)

Twenty-five days after planting(26 Jun 1996)

Midseason(15 Aug 1996)

a_{For each date, means within the same depth followed by the}

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ing maize crop (Table 4). The soil temperature needs to be 42₈C for germination and an air temperature of 62₈C is optimum for the growth of maize (Illinois Agronomy Staff, 1992).

3.3. Crop responses

Maize plant heights were greater with the NT system than the CP and MP systems at 25 days after planting and at midseason during 1995 (Table 9), due in part to higher plant-available water at 25 days after

planting. Other factors that might have contributed to the taller plants with the NT system were a less competition between plants due to lower population or better nutrients and water availability due to pro-tection from erosion with NT system than with the CP and MP systems. During 1996, the soybean plant height was not recorded at 25 DAP due to the smaller size of soybean than maize at this stage. By the midseason, no signi®cant differences were observed in soybean height due to tillage.

The data from the tissue analysis of maize (1995) and soybean (1996) leaves at midseason (Table 10) showed non-signi®cant differences in concentration of all elements except N in 1995 for maize due to tillage. Moldboard plowing was associated with a higher maize leaf nitrogen concentration compared with that of the leaves in the CP and NT systems. This might indicate lower nitrogen immobilization and higher mineralization with the MP system than with the NT or CP systems. Plant uptake of other macro-and micro-nutrients was not affected by tillage in either year (Table 10). This is consistent with the fact that there were no tillage based differences in plant-available water.

Rainfall data (30-year average for southeastern Illinois) and 1989±1996 growing seasons are shown in Table 8. The 30-year average cumulative rainfall during April±September in southeastern Illinois was 60.1 cm. During the study, half of the years (1989, 1991, 1992 and 1994) could be characterized as dry years with a growing season rainfall of 51.9, 43.3, 56.8, and 50.7 cm, respectively. The years with the most below-average rainfall were 1991, and 1994. In

Table 8

Rainfall data during the growing season from 1989 to 1996 at Dixon Springs in southern Illinois Year Rainfall (cm)

Apr May Jun Jul Aug Sep

1989 6.1 4.1 14.3 12.8 10.0 4.6

1990 14.5 28.2 4.4 6.4 10.5 8.8

1991 12.5 8.9 1.8 3.7 4.0 12.4

1992 6.1 6.7 7.6 13.4 3.9 19.1

1993 12.3 13.0 17.8 13.4 10.9 19.4

1994 16.2 1.5 10.2 6.0 9.8 7.0

1995 17.7 22.0 15.2 7.3 8.2 4.8

1996 14.8 14.2 9.0 13.1 1.4 14.8

1989±1996 average 12.5 12.3 10.0 9.5 7.3 11.4

30-Year average 11.2 12.4 9.8 10.3 8.6 7.8

Table 9

Effect of different tillage treatments on soil temperature and plant height at Dixon Springs

Tillage Soil temperature (8C)a 1995 1996 25 DAPb 25 DAP No-till 24.3a 21.0b Chisel plow 24.4a 22.1a Moldboard plow 24.5a 22.1a

Plant height (m)a

1995 1995 1996 25 DAP midseason midseason No-till 0.70a 3.02a 0.89a Chisel plow 0.61b 2.90b 0.84a Moldboard plow 0.61b 2.80c 0.90a

a_{Means for same date and parameter followed by the same letter}

are not significantly different at thep0.05 probability level.

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1991, the driest year, the maize yields were low for all treatments since all plant-available water above the fragipan was extracted from all treatments, including the NT system. In 1994, another year of low rainfall, the soybean yields were low for all treatments, but NT yield was substantially higher than CP and MP yields. The eight-year average rainfall for the April through September period was 63.0 cm which is slightly above the 30-year average.

From 1989 to 1996, the MP system had a signi®-cantly higher plant population in four out of eight years (Table 6) and the NT system had a signi®cantly higher plant population in two out of eight years. In 1989, the NT had a lower plant population (Table 6) compared with that of the MP system which was probably due to insuf®cient soil±seed contact, lower germination, and greater soil strength in the NT system (Kitur et al., 1994). During 1990, 1995, and 1996, the high April and May rainfalls contributed toward lower plant population with the NT system compared with that of the MP system (Table 6). Higher plant population with the MP system than with the NT and CP systems during 1995 and 1996 was also observed. Higher soil temperature and better seed±soil contact with the MP system could have increased the germination compared with that of the NT system during 1995 and 1996. On the other hand, in 1994, the plant population was higher with the NT treatment compared with that of the CP and the MP treatments, which could have been due to relatively greater water availability in the NT system compared with other tillage systems at planting. Four-year average plant population (Table 6) for maize was higher with the NT

system compared with that of the MP and CP systems, while the four-year average soybean population was not affected by tillage treatment.

From 1989 to 1996, tillage affected crop yields only in the years 1989 and 1994 (Table 11). Because of the higher plant population (Table 6) with the MP system, in four out of eight years, plant population was used as a covariant in the yield analysis. For maize yields, plant population was signi®cant as a covariant, but the improvement inr2was only from 0.77 to 0.78. For the soybean yield analysis, plant population was not sig-ni®cant as a covariant. Plant population adjusted crop yields are presented in Table 12. Maize yield was highest for the MP system in the years 1989 and 1991 (Table 12), with the higher yield in early years believed to have been due to better seed±soil contact, germination, lime incorporation, weed control, and mineralization of organic matter (Kitur et al., 1994). The NT maize yields in 1993 and 1995 were higher than the CP and the MP systems and differences were signi®cant in 1995 due to slightly more water and better protection from erosion.

The MP system produced a higher soybean yield than the NT and CP systems in 1990, but later on, soybean yields with the NT system improved com-pared with the MP system. In 1992, 1994 and 1996, the NT system produced a higher soybean yield. Soybean yield with the NT system was higher than with the CP and MP systems due to better plant population in 1994. Since 1994 was a dry year, the NT system could have provided more soil water to soybean at planting and later in the season compared with that of the other tillage systems. This enhanced

Table 10

Effect of tillage on maize and soybean tissue analysis at midseason in 1995 and 1996 at Dixon Springs Tillage Nutrientsa_{(g kg}ÿ1₎

N P S K Mg Ca Na B Zn Mn Fe Cu Al

Maize(1995)

No-till 32.6a 3.6a 1.9a 22.0a 1.5a 4.6a 0.1a 0.005a 0.021a 0.056a 0.115a 0.012a 0.062a Chisel plow 31.8a 3.6a 1.9a 22.9a 1.7a 4.5a 0.1a 0.005a 0.021a 0.068a 0.114a 0.011a 0.058a Moldboard plow 34.0b 3.6a 2.0a 22.6a 1.6a 4.4a 0.1a 0.006a 0.022a 0.067a 0.117a 0.012a 0.060a

Soybean(1996)

No-till 60.0a 4.1a 3.3a 17.0a 3.3a 15.2a 0.1a 0.049a 0.053a 0.109a 0.141a 0.013a 0.063a Chisel plow 61.1a 4.1a 3.3a 16.8a 3.2a 14.2a 0.1a 0.045a 0.054a 0.118a 0.152a 0.013a 0.062a Moldboard plow 61.4a 3.8a 3.3a 16.2a 3.2a 14.8a 0.1a 0.043a 0.052a 0.122a 0.163a 0.012a 0.072a

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soil-water storage could have resulted in an improve-ment in nutrient availability and played an important role in 100% and 60% higher soybean yields with the NT system as compared to MP and CP systems in 1994. Higher crop yield with the NT system than with the MP system in a dry year was also noted by Lueschen et al. (1991). Although the differences in soybean yields in 1996 were not signi®cant by tillage treatment, the NT system had a 7% and 15% higher yield than the MP and CP systems, respectively. Higher yield with NT in the 1996 season was attrib-uted to better plant growth, more soil water, higher organic matter content in the 0±5 cm layer, and more protection from erosion as compared with MP.

The four-year average maize yield was not affected by tillage, while the four-year average soybean yield was higher with NT than with CP and the MP (Table 10). Four-year average soybean yield was 14% higher with NT than with CP and MP systems, while the maize yield was equal in all tillage systems. At the beginning of the experiment, the MP system produced 21% and 11% higher yield compared with that of the NT and CP systems during 1989 and 1990 but with no difference in 1991. After three years, the NT system yields were 3±100% higher than the MP system (Fig. 1) during the 1992±1996 period.

The NT yields were lower in the early years of study, but improved with the passage of time. The NT

Table 11

Effect of different tillage treatments on maize and soybean yield during 1989±1996 at Dixon Springs Tillage Crop yield (Mg haÿ1)a

1989 1991 1993 1995 Averageb

Maize

No-till 8.99b 6.57a 11.79a 11.60a 9.81a

Chisel plow 9.99b 6.10a 11.61a 11.55a 9.74a

Moldboard plow 11.26a 6.60a 10.98a 10.37a 9.80a

1990 1992 1994 1996 Averageb

Soybean

No-till 2.37a 3.74a 2.87a 2.63a 2.90a

Chisel plow 2.62a 3.46a 1.81b 2.27a 2.54b

Moldboard plow 2.62a 3.65a 1.49b 2.43a 2.55b

a_{For each crop, means within the same year followed by the same letter are not significantly different at the}_p

0.05 probability level.

b_{Four-year average.}

Table 12

Effect of different tillage treatments on the covariate (plant population) adjusted maize and soybean yields during 1989±1996 at Dixon Springs Tillage Crop yield (Mg haÿ1)a

1989 1991 1993 1995 Averageb

Maize

No-till 8.98b 6.45a 11.99a 11.37a 9.69a

Chisel plow 9.77b 6.53a 11.66a 11.49a 9.86a

Moldboard plow 10.85a 6.78a 11.13a 9.95b 9.68a

1990 1992 1994 1996 Averageb

Soybean

No-till 2.33a 3.78a 2.89a 2.62a 2.90a

Chisel plow 2.60a 3.50a 1.79b 2.27a 2.54b

Moldboard plow 2.61a 3.68a 1.44b 2.45a 2.55b

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performance relative to MP and CP was better during dry years than wet years, which was also observed by Eckert (1984). Figs. 1 and 2 show the yield trend of conservation tillage compared with the MP system with growing season rainfall (April±September) over time. The percentage change was calculated using the following equations:

NTÿMP=MP 100; (1)

(see Fig. 1), and

CPÿMP=MP 100 (2)

(see Fig. 2).

3.4. Rainfall effects

The NT yields were lower during the three early years of the study. This could have been due to lower organic carbon and nitrogen mineralization and higher immobilization of soil nitrogen with the NT than the MP system (Rice and Smith, 1984), but the NT system out-yielded the MP system during the last ®ve years of study. No-till yields were 5±20% lower than the MP

system in wet years, but were 10±100% higher in relatively dry year (Fig. 1) and NTÿMP was nega-tively correlated (r2 ÿ0.66,p0.07) with growing seasonal rainfall. The higher yields with the NT and CP systems in dry years was probably due to the conservation of more soil water than in the MP system, while yields with the NT and the CP systems were lower compared to that of the MP system in wet years (Fig. 1). The CP yields were lower in the ®rst four years compared to that of the MP system and the CP system out-yielded the MP system from 1993 to 1995 period. Chisel plow yields were 5±10% lower in wet years and 20% higher in dry years as compared to MP system (Fig. 2). The CPÿMP difference was nega-tively correlated (r2 ÿ0.56,p0.15) with growing seasonal rainfall.

Generally, well-distributed rainfall over the grow-ing season resulted in better yields for both, maize and soybean with all tillage systems. Water de®ciency or heavy rains in May could have resulted in yield losses by reducing plant population. Higher rainfall during July and August played a critical role in improving the yield of maize and soybean, which

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was evident from yield responses in 1989, 1990, 1992, 1994 and 1996.

4. Conclusions

Conservation tillage, especially in the NT system, left more crop residue on the soil surface and provided protection to soil from water erosion as against the MP system. During the 1995 and 1996 growing seasons, NT resulted in taller plants, slightly more plant-avail-able water, and lower soil temperature at 25 days after planting. Non-signi®cant differences in all elemental concentrations in leaf except nitrogen were observed due to tillage treatments during 1995 and 1996, sug-gesting no tillage effects on the uptake of nutrients by plants. Nitrogen concentration in leaves was higher in MP system plots compared with that of CP and NT system plots. Although plant population was higher in the MP system during both years, crop yields were higher in the NT system compared with that of the MP system which was probably due to more plant-avail-able water and less erosion. The plant population in NT system which was affected by the lower soil

temperature and poor soil±seed contact during the early growing season.

In the ®rst year, crop yield was higher in the MP system compared with that of the CP and NT systems; however, the NT system produced higher crop yields during the last ®ve years. Tillage did not affect four-year average yield or plant population of maize. Four-year average soybean plant population was not affected by tillage; however, the four-year average soybean yield was higher in the NT system compared with other tillage treatments. Maize yields were equal in all tillage systems as a result of higher MP system yield in the ®rst year, which offset higher CP and NT systems yields during the last two years. Soybean yield was 15% higher in the NT system in comparison with the CP and MP systems. Higher NT soybean yields could be due to a higher amount of residue from previous year's maize, which improved water con-servation. Crop yields were higher in the NT system despite lower plant population, so greater water and nutrient availability per plant may have compensated for the effect of lower plant population. The NT system performed better in dry years by conserving water and the NT yield improved over time. Based on

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eight years of crop yield measurements (four years maize and four years soybean), the NT system appears to have resulted in improved long-term productivity compared with that of the MP and CP systems. The results of this study should be applicable to similar root-restricting, sloping, and moderately eroded soils in Illinois, Indiana, Missouri, and Kentucky.

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