Short-Term Effects of Conversion from Reduced Tillage to Direct-Seeding Mulch-Based Cropping Systems

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Journal of Crop Improvement

ISSN: 1542-7528 (Print) 1542-7536 (Online) Journal homepage: http://www.tandfonline.com/loi/wcim20

Short-Term Effects of Conversion from ReducedTillage to Direct-Seeding Mulch-Based CroppingSystems

Rémy Kulagowski & Anaïs Chailleux

To cite this article: Rémy Kulagowski & Anaïs Chailleux (2015) Short-Term Effects of Conversion

from Reduced Tillage to Direct-Seeding Mulch-Based Cropping Systems, Journal of CropImprovement, 29:5, 650-668, DOI: 10.1080/15427528.2015.1070390

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Short-Term Effects of Conversion from Reduced Tillage to Direct-Seeding Mulch-Based Cropping

Systems

RÉMY KULAGOWSKI1 and ANAÏS CHAILLEUX 21 Department of Crop Production, Chamber of Agriculture of Alpes de Haute Provence,

Oraison, France 2CIRAD, UPR HortSys, Montpellier, France

Conservation tillage is one strategy whereby both sustainability and productivity can be achieved by improving the soil quality. Although reduced tillage (RT) is widely practiced, more conserva- tive strategies, such as direct-seeding mulch-based cropping systems (DMC), are less frequent. Here we assessed the effect of conversion

from RT to DMC in three commercial fields in southern France (inland Mediterranean climate). Two fields were cropped withmaize ( Zea mays L.) and one with sorghum ( Sorghum bicolor L.),

and monitored during 15 months. We found higher soil water potential retention in DMC than in RT at 10, 30, and 60 cm soil depth. Conversely, nitrogen availability was slightly higher in the

RT treatment. Crop development was not affected by the soil practices, but crop yields were higher in the DMC treatment for one maize field and the sorghum field (plus 3.04 t/ha harvested in the

DMC treatment when compared to the RT treatment in the maize field and plus 2.105 t/ha in the sorghum one). This study demon- strates that DMC can provide short-term benefits in farm fields in southern France, but these benefits are not automatic and the

conditions under which they are obtained remain to be clarified.

KEYWORDS cover crop, crop development, maize, nitrogen, sorghum, water potential

Received 3 April 2015; accepted 5 July 2015. Address correspondence to Rémy Kulagowski, Chamber of Agriculture of Alpes de Haute

Provence, Avenue Charles Richaud, 04700 Oraison, France. E-mail: [email protected].

Journal of Crop Improvement , 29:650–668, 2015Copyright © Taylor & Francis Group, LLCISSN: 1542-7528 print/1542-7536 onlineDOI: 10.1080/15427528.2015.1070390

650


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INTRODUCTION

Soil quality has been defined as the capacity of a soil to function withinecosystem boundaries, sustain biological productivity, maintain environmental

quality, and promote plant and animal health (Doran and Parkin 1994). Although soil quality is essential for field productivity, agricultural productioncan adversely affect soil quality. Tillage, for instance, has been shown todamage the natural soil ecosystem by increasing soil compaction, erosion,and disrupting soil fauna communities (Pimentel et al. 1995).

In cereal cropping systems, promoting conservation-tillage practices,such as minimum soil tillage, could reconcile crop productivity and environ-mental sustainability by enhancing ecological services provided by the varioussoil components (Baker and Saxton 2007). Under this management practice,the soil is never plowed, instead reduced tillage (RT), or no-tillage is preferred

and ideally residue from the previous crop is left in the field and cover cropsare grown during non-crop period. A minimum of 30% of the soil surfaceshould be covered with crop residue (Kassam et al. 2009). Conservation tillageis currently practiced on 100 million ha worldwide (Derpsch et al. 2010),predominantly in North and South America, but it is also being adopted toan increasing extent in Australia, New Zealand, and South Asia (Hobbs, Sayre,and Gupta 2008; Triplett and Dick 2008). From 1999 to 2009, the areacultivated under conservation tillage increased at an average rate of 6 millionha/year (Derpsch et al. 2010), primarily with the aim of reducing productioncosts and time (Chantre and Cardona 2014), while also preventing soil ero-sion, improving nutrient content in soils, and retaining soil moisture.

Soil tillage impacts many soil physical properties, including the bulkdensity, pore space and pore-size distribution, water-holding capacity, soil- water content, and aggregation (Spedding et al. 2004; Bronick and Lal 2005).Moreover, mulching with crop residue or cover crops also enhances the soilstructure by affecting aeration and temperature (Khan et al. 2000), and soilbiotic parameters by improving the soil organic matter and fauna content.Mulch cover —by shielding the soil from solar radiation—can also reduce soil- water evaporation (Todd et al. 1991; Holland 2004). The magnitude of real

water gain is high, depending on local agroecosystem characteristics, becausemulch cover increases drainage and induces evaporation from surface residue(Scopel et al. 2004). Nevertheless, the absolute balance seems to be generally positive; hence when soil is covered with mulch, more water is likely to beretained in the soil, where it remains potentially available for crop develop-ment, thus decreasing irrigation demand (Bussière and Cellier 1994; Khaledianet al. 2009). On the other hand, mulch decomposition can result in soil-nitrogen immobilization by microbial communities. This reduces the amount of nitrogen available for the crop in the short term, but generates a nitrogensource available on a long-term scale, i.e., mulch provides a favorable food

Short-Term Effects of Conversion from RT to DMC 651


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source for soil microorganisms, which can enhance organic matter degrada-tion, in turn boosting nitrogen mineralization (Campbell, Ellert, and Jame1993; Mary et al. 1996).

Many conservation tillage practices exist, with different effects on soil

quality and yield. Practices range from RT to direct seeding mulch-basedcropping systems (DMC) (Kassam et al. 2009). The DMC is a term very closeto conservation agriculture (CA) (Kassam et al. 2009). The CA is based onthree principles: 1) minimum soil disturbance, 2) soil cover, 3) crop rotation, while, in fact, DMC gives a narrow focus on seeding and soil-cover practices:it is defined as the combination of direct seeding and permanent soil cover (Séguy, Bouzinac, and Husson 2006; Séguy et al. 2008). In this study, we focusonly on soil-management practices at the year scale, without considering therotation aspects of the cropping system; hence, the term DMC is more accu-rate. Although RT has been widely adopted by farmers in temperate regions of

the world, DMC is a new soil-management strategy that requires a drasticchange in farmers’ habits, and high management standards to implement it well (Ingram 2010). The DMC still requires on-farm experiments guided by agronomists to 1) be adapted to specific local conditions, and 2) increasefamers’ knowledge on this new system (Lithourgidis, Damalas, and Elefther-ohorinos 2009; Ingram 2010). In addition, two main obstacles to DMC volun-tary adoption can be noted: 1) the benefits that may be reaped from DMC aremore perceptible in the long term, but not in the short run (Bolliger et al.2006), thus explaining why farmers are often hesitant to convert to this novelstrategy (Mueller, Klemme, and Daniel 1985), and 2) pests, mainly slugs and

weeds, are often cited as major drawbacks of DMC (Bolliger et al. 2006). Water is the most limiting factor for crop production in southern Europebecause of the erratic annual rainfall distribution (Khaledian et al. 2011),thus highlighting farmers’ interest in reduced tillage in this area (e.g., Ebrüggeand Düring 1999). The adoption of conservation tillage has, however, beenslower in Europe than in other parts of the world, and generally merely involves conversion from plowing (inversion deep tillage) to RT (no-inversionand more shallow tillage) (Lahmar 2010; Scopel et al. 2013). Indeed, farmerstend to adopt innovative practices progressively following step-by-step

changes during transition (Chantre and Cardona 2014); hence RT is oftenused as a transitional cropping system between plowing and DMC. Gainingfurther insight into the changes that occur in farmers’ fields when they switchfrom RT to DMC could help agricultural advisers and practitioners.

It is also essential to quantify the seasonal dynamics of soil water andnitrogen pools in order to understand how production systems could be better managed to sustain the long-term soil productivity (Salinas-Garcia, Hons, andMatocha 1997), but few studies have addressed these issues. Thus, the present study was designed to assess the short-term effects of field conversion from RTto DMC practices on abiotic soil components, crop development, and yield.

We assessed the short-term benefits and drawbacks of DMC practices under

652 R. Kulagowski and A. Chailleux


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realistic field conditions in southern Europe, relative to 1) soil-water andnitrogen contents and dynamics and 2) crop development and yield.

MATERIALS AND METHODSStudy Site and Crop Management Conditions

The present study was conducted in three commercial fields on two different farms that were in the same catchment basin (M1: N 43° 54ʹ 35ʺ; E 5° 53ʹ 36ʺ,M2: N 43° 54ʹ 50ʹ; E 5° 54ʹ 9ʺ and S: N 43° 53ʹ 26ʺ; E 5° 53ʹ 38ʺ, elevation 376 mabove sea level) at Oraison, France. The area is under an inland Mediterra-nean type climate, i.e., sunny with low humidity. It rains less than 90 days per year, with an irregular pattern during the summer. The mean annual rainfall is695 mm, with a mean annual temperature of 12.9°C. The three fields had aclayey loam soil, which is classified under the FAO system (Driessen et al.2001) as a typical Fluvisol: fields M1 and M2 with 23.7% clay, 31.3% silt, 6.1%sand, 2.2% organic matter, and pH 8.3; and field S with 24.1% clay, 31.6% silt,5.9% sand, 2.1% organic matter, and pH 8.4.

The field trial was set up in autumn 2011 in three commercial fields that were previously managed under reduced-tillage practices. Farmers conductedall cultivation operations, thus the three fields differed slightly in their croprotation and management practices. The experiment was carried out on twofields cropped with maize (fields M1 and M2) and on one field cropped with

sorghum (field S). The rotations are described in Table 1, and management practices related to the soil practices applied to each field during the experiment are given in Table 2. The three fields were irrigated using a pivot irrigationsystem in M1 field, a sprinkler system in M2 field, and a hose reel irrigationsystem in S field. We ensured that irrigation was similar between treatments ineach field. Monitoring was carried out during spring and summer 2012.

Experimental Design

Two soil treatments were set up in each field: 1) DMC and 2) RT (tillage to15 cm depth and without a cover crop). Each treatment was replicated threetimes (i.e., 6 plots in total) in a homogeneous area in the center of each field toavoid edge effects. The experimental area was 150 m long and 28 m wide in

TABLE 1 Crop rotations per field

Field Rotation

M1 Rape or winter pea Durum wheat MaizeM2 Winter pea Durum wheat MaizeS Rape or winter pea Durum wheat Sorghum or sunflower



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T A B L E 2 C r o p m a n a g e m e n t p r a c t i c e s c a r r i e d o u t d u r i n g t h e e x p e r i m e n t

F i e l d s M 1 a n d M 2

F i e l d S

M

o n t h

D a t e

F i e l d

O p

e r a t i o n s

D

a t e

O p e r a t i o n

s

A

u g u s t 2 0 1 1

3 0 / 0 8 / 2 0 1 1

M 1

O n l y f o r D M C t r e a t m e n t : C o v e r c r o p d i r e c t

s o w i n g ; i r r i g a t i o n

: t w o t i m e s 1 5 m m

2 5 / 0 8

/ 2 0 1 1

O n l y f o r D M C t r e a t m e n t : C o v e r c r o p

d i r e c t s o w i n g ; i r r i g a t i o n : 2 5 m m

0 8 / 0 9 / 2 0 1 1

M 2

O n l y f o r D M C t r e a t m e n t : C o v e r c r o p d i r e c t

s o w i n g

S

e p t e m b e r 2 0 1 1

2 7 / 1 0 / 2 0 1 1

M 1 , M 2

O n l y f o r R T t r e a t m e n t : 1 2 c m p l o u g h i n g

1 0 / 1 1

/ 2 0 1 1

O n l y f o r R T t r e a t m e n t :

1 3 c m

p l o u g h i n g

F

e b r u a r y 2 0 1 2

2 8 / 0 2 / 2 0 1 2

M 1 , M 2

O n l y f o r R T t r e a t m e n t : 1 5 c m s o i l l o o s e n i n g

2 7 / 0 2

/ 2 0 1 2

O n l y f o r R T t r e a t m e n t :

8 c m d e p t h

t i n e h a r r o w i n g

2 2 / 0 3 / 2 0 1 2

M 1 , M 2

F e r t i l i z a t i o n : 2 0 0 k g

. h a −

1

o f 1 8 – 4 6 N - P

f e r t i l i z e r

2 9 / 0 3 / 2 0 1 2

M 1

M a i z e s o w i n g ( c v . M a g g i C S ® ) : 8 1 0 0 0

s e e d s . h a −

1

( s e e d

t r e a t m e n t : C r u i s e r 3 5 0 ®

[ t h i a m e t o x a m 3 5 0 g . L − 1 ] )

A

p r i l 2 0 1 2

0 9 / 0 4 / 2 0 1 2

M 2

M a i z e s o w i n g ( c v . D K 4 7 9 5 ® ) : 8 1 0 0 0

s e e d s . h a −

1

( s e e d

t r e a t m e n t : C r u i s e r 3 5 0 ®

[ t h i a m e t o x a m 3 5 0 g . L − 1 ] )

M

a y 2 0 1 2

1 1 / 0 5

/ 2 0 1 2

S o r g h u m

s o w i n g ( c v . S o l a r i u s ® ) :

3 5 0 0 0 0 s e e d s . h a −

1

J u n e 2 0 1 2

0 5 / 0 6 / 2 0 1 2

M 1 , M 2

F e r t i l i z a t i o n : 4 4 0 k g

. h a −

1

o f C o t e n ® ( 4 4 % N )

0 8 / 0 6

/ 2 0 1 2

F e r t i l i z a t i o n : 3 9 0 k g . h a −

1

o f

a m m o n i t r a t e ( 3 3 . 5 %

N )

0 5 / 0 6 / 2 0 1 2

M 1 , M 2

I r r i g a t i o n b e g i n n i n g

2 6 / 0 6

/ 2 0 1 2

I r r i g a t i o n b e g i n n i n g

A

u g u s t 2 0 1 2

2 1 / 0 8 / 2 0 1 2

M 2

I r r i g a t i o n e n d ( 3 5 5

m m )

2 1 / 0 8

/ 2 0 1 2

I r r i g a t i o n e n d ( 2 6 0 m m

)

3 1 / 0 8 / 2 0 1 2

M 1

I r r i g a t i o n e n d ( 4 1 0

m m )

O

c t o b e r 2 0 1 2

0 8 / 1 0 / 2 0 1 2

M 2

H a r v e s t

0 4 / 1 0

/ 2 0 1 2

H a r v e s t

1 7 / 1 0 / 2 0 1 2

M 1

654


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each field. The treatments were randomized per field, and each plot was 50 mlong and 14 m wide. The cover crops in the DMC treatments were consistent across fields, consisting of a mixture of species, mainly legumes, having a low C/N ratio (Table 3). Cover crops grew successfully in M1 and S and had abiomass of around 3 t/ha at the first frost. In M2, biomass was lower, i.e.,around 1 t/ha, probably on account of the lack of irrigation after sowing(Table 3).

Tensiometers (Watermark®) were used for measuring the soil capillary

tension. Two tensiometers were placed per plot, one at 10 cm depth and oneat 30 cm. One tensiometer was also added in one plot per treatment at 60 cmdepth. Monitoring was done weekly from seeding to harvest. Soil nitrogencontent between 0–20 cm was measured using a Nitracheck reflectometer method (Roth et al. 1991; Wetselaar, Smith, and Angus 1998). One sample per treatment (i.e., two per field), consisting of 10 sub-samples, was analyzedevery second week. Crop development was measured as the number of leaves per plant, and was monitored weekly on one sample per plot consist-ing of 3 sub-samples from 1 m row transects for the two maize fields (M1 andM2), and within a 0.25 m2 quadrat for the sorghum field (S). Finally, yield

components were measured at maturity in order to compare the productivity.Plants from three randomly selected 2 m row transects were thus sampled ineach plot. Plant density, biomass, number of ears or panicles per plant,thousand-kernel weight (TKW), and grain yield were determined.

Statistical Analyses

All statistical analyses were performed using R software (R Development CoreTeam 2009) with the package geepack. Potential differences in tension (10 and

30 cm-depth) and crop development among treatments were analyzed

TABLE 3 Cover crop composition in the DMC treatment for each field during the previous winter (2011–2012) and characteristics at 15 December 2011

Field CompositionDry matter

(DM) (t.ha−1)Nitrogen content

(% of DM) C/N

M1 Field pea (10 kg.ha−1

), grasspea (10 kg.ha−1

),lentil (5 kg.ha−1), fenugreek (3 kg.ha−1),common vetch (5 kg.ha−1), fava bean(10 kg.ha−1).

2.759 4.125 10.18

M2 Field pea (20 kg.ha−1), grasspea (20 kg.ha−1),lentil (5 kg.ha−1), hairy vetch (5 kg.ha−1),fava bean (20 kg.ha−1).

0.907 4.904 8.57

S Field pea (28 kg.ha−1), grasspea (28 kg.ha−1),fava bean (28 kg.ha−1), lentil (9,5 kg.ha−1),soybean (16 kg.ha−1), oat (14 kg.ha−1),radish (6 kg.ha−1).

4.021 3.647 11.50



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separately for each field using generalized estimating equations (GEE) adaptedto repeated measures across time. A GEE based on normally distributed data with a log link function was applied for the tension measurements; the factorstested were the soil practices and date. Poisson distribution was used to fit the

GEE for crop development and factors tested were also the soil practices anddate. For the tension at 60 cm-depth and nitrogen, a paired t-test was carried out on the data from the three fields but separately for each date, and statisticalanalyses were carried out only when results were available for all fields (fromMarch to September for nitrogen and for the 60 cm-depth tension). The yield-component data were analyzed using an ANOVA for biomass, grain yield, andTKW. A generalized linear model (GLM) designed for Poisson distribution data was used for the number of ears or panicles per plant. In all equations, inter-actions between factors were tested up to the first order.

RESULTS

Soil water tensions (low tensions indicate high soil water potential) wereeither lower in the DMC than in the RT treatment or non-significantly different between the two treatments although within-treatment variation was observed across time. It ranged from 0 kPa in early spring to 200 kPa inlate summer, with a marked increase after irrigation was stopped in Sep-tember (Figures 1 and 2). The soil treatment effect on the 10 cm depthtension was different in each field. For M1, the tension was significantly affected ( P = 0.032), whereas in S it was only marginally affected( P = 0.075) and there was no significant effect in M2 ( P = 0.632). Thedate factor had a significant effect on this tension (M1: P = 0.001, M2:

P ≤ 0.001, S: P ≤ 0.001) (Figure 1). Tension at 30 cm depth was significantly affected by the soil treatment only in S (S: P = 0.023), whereas it was lower in the DMC treatment. Although not significant (M1: P = 0.561, M2:

P = 0.571), the tensions showed the same trend in the two other fields(Figure 1). Again, the date effect was always significant (M1: P = 0.015, M2:

P = 0.004, S: P ≤ 0.001) (Figure 1). Tension at 60 cm depth was significantly

or marginally significantly lower in RT than in DMC only in early August (August 2nd: P = 0.075; August 9th: P = 0.087; and August 16th: P = 0.031)(Figure 2).

Differences between initial nitrogen soil content in the three fields were observed. In March (3/15/2012), nitrogen contents were 50.7 kg.ha−1 and 22.1 kg.ha−1 in M1 and 35.7 kg.ha−1 and 7.8 kg.ha−1 in M2 for RT and DMC, respectively. In S, the nitrogen content measurements wereperformed in May (05/29/2012) and were 81.9 kg.ha−1 and 67.9 kg.ha−1

for RT and DMC, respectively. Overall, nitrogen increased from March to June and then decreased in both treatments (Figure 3). It was slightly

lower in the DMC treatment; statistical results show a marginally



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significant difference for April 5th ( P = 0.056) and for August 23rd( P = 0.067) (Figure 3).

Crop development was continuous throughout the season and was not affected by the soil treatment (soil treatment, M1: P = 0.717, M2: P = 1, S:

P = 0.688), except for field S where the interaction was marginally significant (soil treatment*date interaction, S: P = 0.099) (Figure 4). As expected, the date

FIGURE 1 Soil water tension dynamics over time for the RT and DMC treatments at 10 and

30 cm depth for each field. Mean tensions (± SEM) are shown, and rain and irrigation quantitiesare indicated on the top of the graph for each field.



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FIGURE 2 Soil water tension dynamics over time for the RT and DMC treatments at 60 cmdepth for the three fields. Rain and irrigation quantities are indicated on the top of the graph for each field.



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effect was significant for the three fields (date, M1: P ≤ 0.001, M2: P ≤ 0.001, S: P ≤ 0.001).

Yield components are presented in Table 4. The results varied dependingon the component and field. The plant density was similar between the twotreatments in all fields; aboveground biomass was significantly higher in theDMC treatment for M1 and marginally significantly higher for S, whereas it wassignificantly lower in DMC treatment for M2. The number of ears per plant was similar between the two treatments for maize, contrary to sorghum, which

showed significantly more panicles per plant in the DMC treatment.

FIGURE 3 Nitrogen dynamics over time for the RT and DMC treatments for each field.



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FIGURE 4 Crop development over time for the RT and DMC treatments for the three fields.Mean numbers of leaves per plant (± SEM) are shown.



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T

A B L E 4 Y i e l d c o m p o n e n t s o f t h e t h r e e f i e l d s a n d s t a t i s t i c a l r e s u l t s ( G L M w i t h a d a p t e d d i s p e r s i o n

l a w s )

F

i e l d

P l a n t d e n s i t y

( p l a n t / m

2 )

A b o v e g r

o u n d

b i o m a s s

( t / h a )

E a r s ( o r

p a n i c l e s ) / p l a n t

G r a i n y i e l d

( t / h a )

T K W ( g )

M

1

R T

8 . 1 5 ( ± 0 . 2 8 ) a

9 . 6 5 ( ± 0

. 0 8 ) b

1 . 0 4 ( ± 0 . 0 5 ) a

1 5 . 8 0 ( ± 0 . 5 6 ) b

3 0

9 . 4 4 ( ± 6 . 3 1 ) b

D M C

7 . 7 0 ( ± 0 . 3 3 ) a

1 3 . 3 2 ( ± 1 . 4 1 ) a

1 . 0 4 ( ± 0 . 0 3 ) a

1 8 . 8 4 ( ± 0 . 9 4 ) a

3 3

2 . 4 5 ( ± 4 . 5 8 ) a

d f

1

1

1

1

1

F

0 . 6 4 2

1 0 . 1 0

7

0 . 5 9 0

7 . 3 1 0

6 . 6 0 3

P

v a l u e

0 . 4 6 8

≤

0 . 0

5

0 . 9 4 3

≤

0 . 0 5

≤

0 . 1

M

2

R T

8 . 0 0 ( ± 0 . 4 1 ) a

8 . 5 5 ( ± 0

. 5 4 ) a

0 . 9 8 ( ± 0 . 0 2 ) a

1 4 . 1 4 ( ± 1 . 5 7 ) a

2 6

8 . 9 7 ( ± 6 . 9 7 ) a

D M C

8 . 3 0 ( ± 0 . 3 9 ) a

6 . 8 6 ( ± 0

. 3 5 ) b

0 . 9 8 ( ± 0 . 0 2 ) a

1 4 . 8 8 ( ± 0 . 8 2 ) a

2 7

0 . 5 9 ( ± 5 . 0 4 ) a

d f

1

1

1

1

1

F

0 . 3 0 6

1 1 . 7 4

6

0 . 2 8 1

1 . 0 1 3

0 . 0 3 4

P

v a l u e

0 . 6 1 0

≤

0 . 0

5

0 . 6 2 4

0 . 3 7 1

0 . 8 6 2

S

R T

1

3 . 0 4 ( ± 0 . 8 7 ) a

4 . 6 6 ( ± 0

. 2 5 ) b

1 . 1 3 ( ± 0 . 5 3 ) b

5 . 4 5 ( ± 0 . 2 0 ) b

2 0 . 8 6 ( ± 0 . 6 0 ) b

D M C

1

1 . 5 6 ( ± 0 . 8 7 ) a

5 . 9 7 ( ± 0

. 3 0 ) a

1 . 4 3 ( ± 0 . 5 4 ) a

7 . 6 0 ( ± 0 . 3 2 ) a

2 3 . 9 9 ( ± 0 . 4 4 ) a

d f

1

1

1

1

1

F

2 . 5 5 4

7 . 0 5 9

4 . 3 4 7

3 3 . 0 3 9

1 6 . 6 6 6

P

v a l u e

0 . 1 8 5

≤ 0 . 1

≤

0 . 0 0 1

≤

0 . 0 0 1

≤

0 . 0 5

( T K W ) 1 0 0 0 - k e r n e l w e i g h t .

M

e a n s f o l l o w e d b y t h e s a m e l e t t e r i n

c o l u m n a r e n o t s i g n i f i c a n t l y d i f f e r e n

t a t P ≤

0 . 0 5 , a n d m e a n s f o l l o w e d b y t h e s a m e i t a l i c l e t t e r i n c o l u m n a r e

n o t s i g n i f i c a n t l y

d

i f f e r e n t a t P ≤

0 . 1 .

661


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Concerning yield, grain production was significantly higher in the DMC treat-ment for M1 and S, and for M2, the difference was not significant although the yield was also numerically higher in the DMC treatment. Finally, TKW wassignificantly higher in the DMC treatment in S, marginally significantly higher

in M1 and only numerically higher in the M2 field (Table 4).

DISCUSSION

This experiment was focused on the conversion process in situations whenfarmers switch from RT to DMC, in order to assess any short-term advan-tages and drawbacks. The experiment was carried out in three different commercial fields and on two different crops to assess whether the

observed effects were generally applicable. The results showed either better soil water potential in DMC than in RT or no significant difference betweenthe two treatments, and slightly lower nitrogen soil content in DMC. Cropdevelopment was not affected by the soil treatment —it seems that different advantages and drawbacks of each practice ultimately resulted in similar crop development. In addition, grain yields were higher in the DMC treat-ment, despite the difference was statistically significant only in two fieldsover the three studied.

The DMC treatment showed a potential to increased soil water tensioncompared to RT, thus reducing water stress risks for the crop. However, in

some fields no statistically significant differences were observed, highlightingthat other factors impacted soil water content and lowered the benefits of DMC on this parameter. When benefits were observed, it could be the con-sequence of 1) reduced evaporation, thanks to the cover crop residue mulchlayer on the soil surface (Holland 2004; Scopel et al. 2004), 2) soil faunapreservation, in particular earthworms, thus improving water infiltration(Emmerling 2001; Pelosi, Bertrand, and Roger-Estrade 2009), 3) well-struc-tured soil, resulting in better infiltration and water retention (Bronick and Lal2005; Pagliai, Vignozzi, and Pellegrini 2004; Thierfelder and Wall 2010), and 4)

reduced transpiration on account of potentially reduced crop growth in theDMC treatment. However, we found higher aboveground biomass in field M1and S where tensions were lower in DMC treatment, and a lower above-ground biomass in M2 where tensions were not statistically significantly different; hence this last explanation is unlikely to contribute to the differencesobserved in the soil water potentials. These results support the findings of previous studies carried out in Europe (Khaledian et al. 2011, 2012) andelsewhere (e.g., Jones, Moody, and Lillard 1969; Mulumba and Lal 2008). Accurate control of irrigation tailored to DMC could allow potential water savings even during the conversion period, while maintaining a sufficient

available water supply for the crop.



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The soil nitrogen content was slightly lower in the DMC treatment in the0–20 cm horizon. Previous studies assessing the issue of soil nitrogen contentsunder different soil tillage conditions showed that nitrogen was more concen-trated in the surface horizon in no-till treatments, but that the global soil

nitrogen content was relatively similar (Dick 1983; Franzluebbers and Hons1996; Puget and Lal 2005). In our study, the nitrogen content was slightly affected by soil practices (marginally significant differences only in two datesover six tested). It is possible that the significance of differences was under-estimated because of differences between fields. Indeed, fertilization strategies were variable between fields and C/N ratio and biomass of the previous cover crops were different. Previous cover crop consumes/provides more or lessnitrogen 1) during their growing period and 2) for their degradation. Indeed,the degradation of plant residue with a high C/N ratio requires more nitrogenthan the degradation of residue with a low C/N ratio (Paul and Juma 1981;

Bengtsson et al. 2011). Slightly lower soil nitrogen content in the short run inDMC might be due to the residue from the previous crop, i.e., durum wheat for all fields, which negatively affected the nitrogen content of the DMCtreatment because of the high C/N ratio. Note also that, in the RT treatments,the soil is mechanically tilled, thus causing mineralization and release of nitrogen on a short time scale.

Soil organic matter dynamics and nutrient cycling are closely related tothe microbial driven processes of nutrient immobilization and mineralization(Duxbury et al. 1989). We noted a nitrogen peak in May, probably because of the warm temperatures (Srivastava 1992; Schulten and Hempfling 1992; Lein-

weber, Schulten, and Körschens 1994; Franzluebbers, Hons, and Zuberer 1995), and a later peak in June following fertilization treatments. The nitrogencontent then dropped as a result of plant consumption and potential leaching.

Soil practices had no impact on the crop development and had a variableimpact on the yield components investigated. The DMC seemed to have aslight negative impact on the density and a positive impact on the above-ground biomass, except for M2, maybe owing to the lower cover cropbiomass in this field. The DMC and RT showed similar numbers of ears per plant in maize fields, but not in sorghum fields as this crop had more panicles

in DMC than in RT, highlighting a potential difference in response betweenplant species for this yield component. Nevertheless, this possible explanationshould be assessed in further experiments. The TKW and grain yield werehigher in DMC for the tree fields. Benefits of DMC over RT regarding yieldseem to be possible in the short term, as observed in two fields over the threestudied (no significant difference regarding grain yield observed in the thirdone), encompassing different crops, different cover crops, and slightly differ-ent crop management strategies. In a four-year experiment in Greece, Lithour-gidis, Tsatsarelis, and Dhima (2005) found no significant differences betweenthe number of emerged corn plants following a winter wheat in RT and in no-

tillage. They also did not find significant differences in corn biomass and yield



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between these two tillage systems. These differences with our results might bedue to the presence of the cover crop in our study. Moore, Gillespie, andSwanton (1994) compared soybean growth on bare and mulched plots andfound a 35% reduction in soybean emergence under the cover crop but no

differences in yield. Comparatively, the density reduction was lower in our experiment, i.e., 5% in M1 and 11% in S. Moore, Gillespie, and Swanton ( 1994)observed that soybean plants from mulched plots produced more seeds per plant and had a greater total seed weight than the plants grown in bare soilplots. The number of pods per plant was, however, similar for all treatments.The authors hypothesized that the lower density in the DMC treatment wasattributable to pest damage (seedcorn maggot) and that the final similar yield was due to the better development of plants in the mulched plot as compared with plants that suffered drought stress in the unmulched plots. Similarly, inour experiment, some plants could have been destroyed by slugs, which were

numerous in the DMC treatment (Kulagowski and Chailleux 2013), and thesignificantly higher yield observed in the DMC treatment could be explainedby the better soil water potential retention and lower plant density, whichcould have promoted plant development.

This study highlighted the short-term impacts of conversion to DMC prac-tices in farmers’ fields that had been previously managed under RT on soil water potential and nitrogen, crop development, and yield. The results showed 1)benefits of DMC relative to soil water potential, but slight detrimental effect onnitrogen content, and 2) that short-term benefits of DMC on grain yield arepossible, but not automatic, under our pedoclimatic conditions. Further studies

are required to identify the conditions that lead to short-term benefits on cropproduction, to be in a position to advice farmers during this critical period.

ACKNOWLEDGMENTS

We express our thanks to the following farmers for allowing us access to thestudy sites and for crop management: Guy Giraud and Robert Ristorto. We

thank Alexandra Jestin for the advices on the statistical analyses, Laura Riggifor useful comments on the manuscript.

FUNDING

We thank the Chamber of Agriculture of Alpes de Haute Provence for fundingRémy Kulagowski.



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Short-Term Effects of Conversion from Reduced Tillage to Direct-Seeding Mulch-Based Cropping Systems

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