the consequences of wheel-induced soil compaction and subsoiling for silage maize on a sandy loam...

Soil & Tillage Research 70 (2003) 175–184

The consequences of wheel-induced soil compaction andsubsoiling for silage maize on a sandy loam soil in Belgium

Frank Nevens∗, Dirk ReheulDepartment of Plant Production, Ghent University, Coupure Links 653, 9000 Gent, Belgium

Received 26 March 2002; received in revised form 11 November 2002; accepted 18 November 2002

Abstract

In Belgium, growing silage maize in a monoculture often results in increased soil compaction. The aim of our researchwas to quantify the effects of this soil compaction on the dry matter (DM) yields and the nitrogen use of silage maize (ZeamaysL.). On a sandy loam soil of the experimental site of Ghent University (Belgium), silage maize was grown on plots withtraditional soil tillage (T), on artificially compacted plots (C) and on subsoiled plots (S). The artificial compaction, induced bymultiple wheel-to-wheel passages with a tractor, increased the soil penetration resistance up to more than 1.5 MPa in the zoneof 0–35 cm of soil depth. Subsoiling broke an existing plough pan (at 35–45 cm of soil depth). During the growing season,the release of soil mineral nitrogen by mineralisation was substantially lower on the C plots than on the T and S plots. Silagemaize plants on the compacted soil were smaller and flowering was delayed. The induced soil compaction caused a DM yieldloss of 2.37 Mg ha−1 (−13.2%) and decreased N uptake by 46.2 kg ha−1 (−23.2%) compared to the T plots. Maize plantson compacted soil had a lower, suboptimal nitrogen content. Compared with the traditional soil tillage that avoided heavycompaction, subsoiling offered no significant benefits for the silage maize crop. It was concluded that avoiding heavy soilcompaction in silage maize is a major strategy for maintaining crop yields and for enhancing N use efficiency.© 2002 Elsevier Science B.V. All rights reserved.

Keywords:Belgium; Nitrogen uptake; Silage maize yield; Soil compaction; Soil mineral nitrogen; Subsoiling

1. Introduction

In Flanders, silage maize (Zea maysL.) is oftengrown in monoculture, being cropped repeatedly onthe same land. Negative consequences of this practiceare a high incidence of root disease, greater weedpressure and compacted soil (Alblas and Wanink,1990). Soil compaction arises from an imbalance be-tween the forces (or pressures) exerted by soil tillageor wheel traffic and the bearing capacity of the soil(Tijink, 1990). On silage maize land, it is caused by

∗ Corresponding author. Tel.:+32-9-264-90-67;fax: +32-9-264-90-94.E-mail address:[email protected] (F. Nevens).

using heavy harvesting equipment, often late in theseason on a wet soil. Secondly, early spring tillageis often postponed as long as possible to extend theperiod for spreading livestock manure. Subsequently,the ploughed and loose soil is compacted artificially tosome degree for optimal seedbed preparation (Booneet al., 1986). In addition to over-winter persistenceof wheel-induced soil compaction, definite struc-tural changes are caused by this spring wheel traffic(Voorhees et al., 1978).

The direct consequences of increased soil com-paction for the crop are impaired root growth androot function, caused by diminished soil aeration andincreased mechanical resistance in the soil (Tardieu,1994). In compacted soils, plant root length is reduced

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176 F. Nevens, D. Reheul / Soil & Tillage Research 70 (2003) 175–184

(Ikeda et al., 1997; Sherlaw and Alston, 1984) andthe root system develops superficially (Boone et al.,1987; Tardieu, 1988). As a consequence, the roots ex-plore a relatively small soil volume and they intercepta limited amount of water and nutrients (Oussibleet al., 1992). Furthermore, soil compaction decreasesmicrobial biomass (Kaiser et al., 1991) and enzymeactivity (Dick et al., 1988) in the soil. As a result,mineralisation is depressed (Breland and Hansen,1996; De Neve, 2000). Substantially higher deni-trification rates were observed in compacted soilscompared with non-compacted soils (Bakken et al.,1987; Ball et al., 1999). Haunz et al. (1992)foundthat compaction of a loamy sand soil during a wetyear resulted in a reduction of net mineralisation by33% and an increase of denitrification by 20%.

The reduced root system and the decreased nutrientavailability in compacted soils cause lower nutrientuptake by the growing crop (Dolan et al., 1992; Grathand Håkansson, 1992) and hence decreased shootgrowth and crop yield (Veen et al., 1992). Waninket al. (1990)reported silage maize yield depressionsof 0–38% when the 30–50 cm soil layer was heavilycompacted.Mouraux et al. (1990)found 19% loss ofsilage maize dry matter (DM) yield (=−3.6 Mg ha−1)on soils heavily compacted in dry circumstances; on awet soil the loss was 41% (−7.6 Mg ha−1). Owing toclay soil compaction, corn DM yield losses of 30% ina dry year and up to 50% in a wet year were recordedby Raghavan et al. (1979).

Increasing nitrogen (N) fertilisation alleviates oreven compensates for the negative yield effects of soilcompaction in some cases (Douglas and Crawford,1998; Sherlaw and Alston, 1984). However, higherrates of N to overcome potential yield losses on com-pacted soils also increase the potential risk of nutrientlosses (Lipiec and Stepniewski, 1995).

Soil loosening by subsoiling aims at eliminatingexisting soil compaction and preventing a reductionin soil rooting depth (Carter, 1988). Ide et al. (1987)found that the removal of a plough pan on a silt loamsoil resulted in a mean yield increase of 5–10% forcereals and sugar beet (Beta vulgarisL.). Hipps andHodgson (1987)found that subsoiling did not increasethe number of roots nor the water uptake by wheat(Triticum aestivumL.) in dry periods, even though soilpenetration resistance was substantially reduced. AlsoFrost (1988)observed that deep soil loosening gave

no or even adverse effects on grass yields, owing to alack of compaction in the soils prior to loosening.

In Flanders, 153,000 ha (23% of the total agricul-tural area) are cropped with silage maize. A large partof this maize is grown in monoculture and high ratesof slurry are applied, usually supplemented with min-eral fertiliser N.

The aim of our research was to quantify the ef-fect of soil compaction on monoculture silage maizeDM yield, N uptake and N content. We hypothesisedthat avoiding heavy soil compaction enhances soil Nmineralisation and makes silage maize a more effi-cient user of applied N. We applied a relatively highlevel of soil compaction to illustrate a worst casescenario. Nevertheless, visual post-harvest observa-tions indicate that on numerous Flemish maize landplots severe soil compaction actually occurs. We alsowished to see whether subsoiling a compacted soiloffered any benefits for silage maize DM yields andN use.

2. Materials and methods

2.1. Site

The trial was established during the spring of 1993on a sandy loam soil at the experimental site of GhentUniversity at Melle (50◦59′N, 03◦49′E, 11 m abovesea level). The soil is classified as an Albeluvisolaccording to the FAO soil classification. The clay,silt and sand contents of the soil layers are sum-marised inTable 1. The carbon content of the topsoillayer (0–30 cm) was 23 g kg−1. According to localtarget values for sandy loam soils (12–16 g C kg−1,Vanongeval et al., 2000), this was relatively high.

Table 1Clay, loam and sand contents (g kg−1) of the soil at the experi-mental site of Melle

Soil depth(cm)

Clay(0–2�m)

Silt(2–50�m)

Sand(>50�m)

0–27 123 566 31128–35 148 565 28736–55 230 504 26656–80 115 202 68381–100 69 85 846101–125 81 102 817

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2.2. Compaction treatments

Three treatments were established on three replicateblocks:

Compacted soil(C). The soil was artificially com-pacted by a wheel-to-wheel tractor passage. Thetractor weight was approximately 5 Mg. Double rearwheels were mounted, the tire type was Michelin12.4R36 and the inflation pressure was 130 kPa. Thistreatment was carried out twice, 2 days before and2 days after the spring ploughing of 24 April 1993.On 26 April, the topsoil (0–30 cm) moisture content(determined gravimetrically) was on average 17.2%(w/w). The subsequent seedbed preparation was car-ried out as on the control plots (T).

Control soil (T). The plots were tilled in the tra-ditional way used in the experimental area, to avoidheavy soil compaction. Ploughing was carried out on24 April 1993, the ploughing depth was 27 cm. A pas-sage with a Cambridge roller followed; the seedbedwas prepared with a rotary harrow on 28 April 1993.

Loosened soil(L). The soil was loosened with asubsoiler (working depth ca. 75 cm) on 22 April. Sub-sequently, tillage activities were carried out as on con-trol treatment T.

2.3. Crop data

On 28 April, silage maize “Magda” was sown at10.3 kernels m−2 (the inter row distance was 75 cm)after mineral fertilisation had been applied at a rateof 90 kg N ha−1 (ammonium nitrate 27% N) and13 kg P ha−1 (triple superphosphate 18.8% P). 50 Mgof cattle slurry (200 kg N+ 39 kg P ha−1) and 48 Mgof farmyard manure (264 kg N+ 120 kg P ha−1) wereapplied on 17 November 1992 and 10 April 1993,respectively. This meant that the total amount of ap-plied N was high, even exceeding the silage maize Nfertilisation limit set by the current Flemish manurelegislation: 275 kg of total N ha−1 year−1 (B.S., 2000).

2.4. Soil measurements

On 26 April, soil penetration resistance was mea-sured using a static penetrometer with manual drive-in(Stiboka Penetrograph) to quantify the intensity of thewheel-induced soil compaction and of the soil loosen-ing (Woojung, 1986). The penetrometer cone with a

base surface of 10−4 m2 and a cone angle of 60◦ en-abled us to measure a maximum penetration resistanceof 5 MPa. For each treatment, penetration resistancewas measured on two random areas per block. Thetopsoil (0–30 cm) moisture content (determined gravi-metrically) on 26 April was on average 17.2% (w/w).

During the growing season, the soil was sampledeight times (27 April, 3 June, 25 June, 15 July, 9August, 3 September, 29 September and 26 October)to determine mineral N content. Three soil layerswere sampled using a gauge auger: 0–30, 30–60 and60–90 cm of soil depth. For each treatment, sam-ples were taken at two randomly selected spots perblock. Subsequently, the six samples of each treat-ment were bulked. Two sub-samples of 30 g eachwere used for analysis. The 0–30 cm samples wereextracted with KCl (1 N) and N (ammonia and nitrate)was determined colorimetrically using a ContinuousFlow Analyser (De Meyer, 1993; Hofman, 1983).The deeper soil samples were extracted with a 1%KAlSO4

2− solution. Nitrate was then measured with anitrate-specific electrode (Cottenie and Velghe, 1973;Hofman, 1983). Between sampling and analysis thesoil samples were deep-frozen (−18◦C) and theywere not dried before extraction.

2.5. Plant measurements

On each block and for each treatment, the heightof 20 silage maize plants was measured on 3 June, 25June and 15 July. On the same plants, male and fe-male flowering was counted on 21 July. On 3 June, 25June, 15 July and 9 August, a 4 m row of silage maizeplants (=3 m2) of each treatment was harvested in eachblock. The DM yield as well as the N content of theentire above-ground plant parts were determined. Ontwo 6 m2 subplots in each block, the end-of-season (21September) silage maize DM yields were determinedfor each treatment. The plant parts (leaves and stalks)and the ears were weighed separately. The plant partswere chopped and dried for 12 h at 80◦C, the earswere dried for 12 h at 80◦C, subsequently for 4 h at105◦C. The N contents of the maize samples (Kjel-dahl method;AOAC, 1990) were determined and theN uptakes were calculated. The found N contents ofthe silage maize (at harvest stage and during the grow-ing season) were compared with optimum target val-ues proposed byPlénet and Cruz (1997).


Fig. 1. Maximum temperatures, minimum temperatures and precipitation in Melle, 1993 and the 1962–1999 average (=“normal”).

2.6. Weather data

The monthly average maximum and minimumair temperature as well as the total rainfall on theexperimental site are summarised inFig. 1. Datafor the trial year 1993 as well as long-term av-erages (1962–1999) are presented. The trial yearwas characterised by warmer than usual weather inearly summer, but approximately equal amounts ofprecipitation.

3. Results and discussion

3.1. Penetration resistance

At the time of compaction by wheel-to-wheel tractorpassages, the soil was relatively dry. This was not sur-prising following the dry and warm months of Marchand April (Fig. 1). Nevertheless, significantly higherpenetration resistances on the C plots were observed(Fig. 2). In contrast with observations ofVoorheeset al. (1978)on a silty clay loam, this higher pene-tration resistance following intensive wheel trackingpersevered into the deeper soil layers (>45 cm).

Although penetrometers do not measure the exactpressures that roots must exert to penetrate the soil,they do provide useful measures of the resistance ofthe soil to which root growth may be referred (Booneet al., 1986; Sherlaw and Alston, 1984). Boone andVeen (1982)found a close curvilinear relation be-tween maize root extension and cone resistance andthey concluded that the lower critical limit of me-chanical impedance for maize (the soil conditionswhich cause a decrease in root growth rate of 50%)corresponds with a penetration resistance of 1.5 MPa.In our compacted soil this value was surpassed, alsoin the top soil layers. The measured penetration re-sistance on the C plots came close to values foundby Mouraux et al. (1990)in a comparable soil. Thelatter authors also characterised the applied treat-ment as a heavy compaction on a relatively dry soil(moisture content 21%). On the present control plots,an increase of the soil penetration resistance belowa soil depth of approximately 30 cm was observed.Repeated tractor driving in the furrow during annualploughing probably caused this compaction (Van denAkker and Lerink, 1990). The subsoiling treatmentwas successful in breaking this plough pan, as signif-icantly lower penetration resistances occurred in the


Fig. 2. Soil penetration resistance measured on 26 April 1993 (C: compacted soil; T: traditional soil tillage; L: loosened soil) Bars representthe LSD atP = 0.05.

35–45 cm soil layer (Fig. 2). Nevertheless, up to 30 cmof soil depth, the T and L penetration resistance curvescoincided, indicating that the “traditional” treatmentcould reasonably be considered to be a soil manage-ment which avoids heavy soil compaction relativelywell.

3.2. Plant height and flowering

Table 2summarises the heights of the silage maizeplants. In accordance with the findings ofRaghavanet al. (1978), we observed that the plants on the com-pacted soil were significantly smaller than those on

the control or subsoiled plots. At maximum height(15 July), the maize plants on the C plots were17.9% smaller than the ones on the T plots.Mourauxet al. (1990)found a comparable effect: at maximumheight, maize plants on a compacted soil were 19%smaller than plants on control plots.Hoek (1986),on the other hand, reported no visible plant heightdifferences between maize plants on compacted andnon-compacted soil, despite an end-of-season DMyield loss of 2 Mg ha−1 due to soil compaction. Themaize plants on the subsoiled plots were higher thanon the control plots but even the maximum difference(+5.8% on 15 July) was not significant.


Table 2Plant height (m), proportion of flowering plants (%) and number of ears (m−2)

Soil treatment Statistical significance

Compacted Usual Loosened

Plant height3 June 1993 0.442aa 0.456a 0.458 NSRelativeb 96.9 100.0 100.4

25 June 1993 1.29b 1.41a 1.43a ∗∗Relative 91.2 100.0 101.2

15 July 1993 1.98b 2.41a 2.47a ∗∗Relative 82.1 100.0 105.8

Flowering 21 July 1993Male 80.3 90.5 87.7 NSRelative 88.7 100.0 96.9

Female 36.0 53.6 56.7 NSRelative 67.2 100.0 105.8

Number of ears10.4 10.0 10.3 NS

Relative 103.3 100.0 102.5

a Values within the same row with different letters are significantly different atα = 0.05 (Newman–Keuls test).b Traditional treatment= 100.∗∗ 0.001< P < 0.01.

Although male as well as female flowering percent-ages (21 July) were not significantly different amongtreatments, there was a trend for a lower proportionof maize flowering on the compacted soil (Table 2).Mouraux et al. (1990)found a statistically significantdelay in female flowering of maize plants on com-pacted soils. In contrast with these authors, a differ-ence in the number of harvested ears was not observedin our trial (Table 2).

3.3. End of season DM yields

Table 3summarises the silage maize yields at theend of the growing season (21 September 1993).Compared with the T treatment, the silage maize onthe compacted soil yielded 2.37 Mg ha−1 less DM, asignificant reduction of 13.2%. The observed yield ef-fect is in line with the results ofMouraux et al. (1990),who, under comparable circumstances found a loss of3.6 Mg ha−1 DM on compacted plots, correspondingwith 19% of the DM yields on control plots.

The highest part of the yield loss on our C plotswas composed of leaves and stalks (smaller plants).

This was also reflected in the ratio of vegetative partsto ears: 0.83 and 0.95, respectively, on the C and onthe T plots. We should add that our trial was carriedout during a season that was relatively dry, particu-larly during the period when the soil was compacted(Fig. 1). It is well known that, in fine-textured soils,the yield reduction effect of compaction is most pro-nounced when it is induced under wet conditions.Moreover, our soil had a relatively high organicmatter content, and negative yield effects of soilcompaction are known to be smaller in soils withhigh organic matter contents (Mouraux et al., 1990;Wanink et al., 1990).

The DM yield data concur with the conclusionsof Arvidsson and Håkansson (1991), that soil com-paction leads to substantial economic losses, andwith Raghavan et al. (1978), that the control of soilcompaction significantly improves the efficiency andprofitability of plant production. However, comparedwith the T soil treatment, subsoiling resulted in anon-significant total DM yield increase of only 3.4%and no significant differences in DM contents wereobserved.


Table 3Silage maize DM yield (Mg ha−1) and N uptake (kg ha−1)

Soil treatment Statistical significance

Compacted Traditional Loosened

DM yieldVegetative parts 7.07ba 8.74a 8.89a ∗∗Relativeb 80.9 100.0 101.7

Ears 8.53a 9.23a 9.69a NSRelative 92.4 100.0 104.9

Total 15.60b 17.97a 18.58a ∗Relative 86.8 100.0 103.4

N uptakeVegetative parts 50.2b 76.0a 77.3a ∗∗∗Relative 66.1 100.0 101.7

Ears 102.4b 122.8a 126.0a ∗Relative 83.4 100.0 102.6

Total 152.6b 198.8a 203.3a ∗∗Relative 76.8 100.0 102.3

a Values within the same row with different letters are significantly different atα = 0.05 (Newman–Keuls test).b Traditional treatment= 100.∗ 0.01 < P < 0.05.∗∗ 0.001< P < 0.01.∗∗∗ P < 0.001.

Fig. 3. Observed and critical N contents (Plenet and Cruz, 1997) of silage maize (C: compacted soil; T: traditional soil tillage; L: loosenedsoil; 1: 3 June; 2: 25 June; 3: 15 July; 4: 9 August; 5: 21 September 1993).


3.4. N uptake and N content

Above-ground silage maize parts took up153 kg N ha−1 on the compacted soil (Table 3). Thiswas significantly less than the uptake on the control oron the subsoiled plots where 199 and 203 kg N ha−1,respectively, were exported. Again, the leaves andstalks accounted for the highest part of the loss.Voorhees (1985)also found a substantial reduction(−45%) of N uptake for maize grown on a soilcompacted with a 20 Mg vehicle. Comparing thesilage maize on the C plots with the maize on the Tplots, we observed that the relative N uptake losses(−23.2%) were higher than the relative DM yieldlosses (−13.2%). This indicated that the N content ofthe silage maize plants was lower on the compactedsoil. Fig. 3 representing the measured N content dur-ing the growing season and at harvest confirms thisconclusion. Except for the very young plants, themaize on the compacted plots had a suboptimal Ncontent throughout the growing season, when com-pared to the optimum target values proposed byPlénetand Cruz (1997).

A first possible cause of the yield loss and the re-duced N uptake, as well as the lower N content on theC plots, was an impaired maize root growth on com-pacted soils; the latter fact was observed in a similarexperiment in Melle during 1991 (Nevens et al., 1992).

A second cause of the negative compaction effectscould be a decreased N mineralization on the C plots.Although we have no statistical evidence, on the Land T plots we actually observed higher contents ofmineral soil N during the growing season, comparedto the compacted plots. On compacted plots, the in-crease in soil mineral N from 24 April to 3 June was63 kg N ha−1. On the subsoiled and “traditional” plots,this increase was, respectively, 208 and 205 kg N ha−1.

In the 1991 experiment (Nevens et al., 1992), it wasalso confirmed that additional N fertilisation allevi-ated the negative yield effects of the soil compaction(Rooms, 1992). However, the current Flemish legisla-tion limits N fertilisation and, as mentioned before, inthe present experiment of 1993, the applied amount offertiliser N already exceeded the maximum allowedrate of 275 kg N ha−1. Nevertheless, negative soil com-paction effects occurred. Hence the alleviation of soilcompaction by increased N fertiliser can no longer beconsidered a valid alternative.

4. Conclusions

Soil compaction reduced silage maize DM yieldand N uptake significantly due to a decreased miner-alization and probably due to impaired root growth. Inline with Håkansson et al. (1995)andO’Sullivan andSimota (1995), we conclude that, apart from economiclosses, soil compaction had a considerable impact onN release in the soil and on N uptake by the silagemaize crop. In the past, an increased fertiliser N appli-cation was considered to be a compensatory measurefor the negative effects of soil compaction. However,such a practice does not accord with a contemporaryconcept of sustainable agriculture that aims at a reduc-tion of N application in order to reduce nitrate levelsin soil and water. To put it another way, avoiding soilcompaction is a means to reach higher yields with thesame amount of N or to reduce N fertilisation withoutyield losses (Soane and van Ouwerkerk, 1995).

Rational ways to manage or alleviate soil com-paction are the use of low ground pressure field trafficsystems (Tijink et al., 1995), increasing soil organicmatter content (Soane, 1990; Ohu et al., 1985) andusing suitable crop rotations (Alblas and Wanink,1990). Coping with soil compaction should not bestudied as an isolated factor but as an integral part ofthe soil–plant-management system (Håkansson et al.,1995).

Loosening a soil that was not severely compactedoffered no significant advantages.

Acknowledgements

Our research was supported and financed by theBelgian Ministerie voor Landbouw en Middenstand,Directoraat-Generaal Onderzoek en Ontwikkeling(DG6).

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the consequences of wheel-induced soil compaction and subsoiling for silage maize on a sandy loam...

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