Performance and environmental effects of forageproduction on sandy soils. IV. Impact of slurryapplication, mineral N fertilizer and grassunderstorey on yield and nitrogen surplus of maizefor silage

M. Wachendorf*, K. C. Volkers*, R. Loges*, G. Rave† and F. Taube*

*Institute of Crop Science and Plant Breeding – Grass and Forage Science/Organic Agriculture, University of Kiel,

Kiel, Germany, and †Variationsstatistik, University of Kiel, Kiel, Germany

Abstract

A field experiment was conducted from 1998 to 2001 to

measure the performance and environmental effects of

a maize crop (Zea mais L.) in a continuous production

system with and without a grass understorey (Lolium

perenne L.), with varied N inputs. The experiment was

located on a sandy soil in northern Germany and

comprised all combinations of slurry application rate (0,

20, 40 m3 ha)1) and mineral N fertilizer (0, 50, 100,

150 kg N ha)1). Understorey treatments included

maize with and without perennial ryegrass. Net energy

(NEL) yield of maize increased with mineral N applica-

tion rate but reached a plateau at high rates. Increase in

yield of dry matter because of mineral N fertilizer was

lower with increased slurry application rate. Neither

slurry and mineral N application nor a grass understo-

rey affected NEL concentration of maize, whereas crude

protein (CP) concentration increased with increase in

application of slurry and mineral N fertilizer. Nitrogen

supply by slurry or mineral fertilizer had no effect on

the amount of N in the grass understorey after the

harvest of maize. The average amount of N bound

annually in the understorey was 60 kg N ha)1. The

reduced biomass of the understorey because of

enhanced maize competition was compensated for by

an increased CP concentration in the grass. The grass

understorey affected the NEL yield of maize negatively

only at very low levels of N input but increased the N

surplus at all levels.

Keywords: maize, silage, nitrogen surplus, grass under-

storey, slurry

Introduction

Maize production for whole crop silage has gained

much popularity in Europe over the last decades. The

area of maize harvested for silage in Europe is around

13 million hectares, with France and Germany being

the two most important countries in Western Europe

with well over a million hectares each (Wilkinson et al.,

1998). Several technological advances have encouraged

the increased production of maize silage: (i) early-

maturing varieties became available, which are better

adapted to the northern European climate, allowing the

harvest 2–3 weeks earlier than that was the case a

decade ago, (ii) its cultivation is technically straightfor-

ward, (iii) many measures can be carried out with high-

capacity equipment by hired contractors and (iv) the

plant shows a high tolerance to continuous cropping

and high amounts of organic fertilizers. The develop-

ment of new feeding systems (e.g. total mixed rations)

and an improved understanding of the role of supple-

mentary protein in diets based on silage maize

undoubtedly induced farmers to increase the amount

of maize in the diet of ruminants. The low crude protein

(CP) concentration of mature silage maize makes it an

ideal component in protein-rich grass-based rations and

the high quality of maize starch has led to a high

appreciation of its value mainly in intensive dairy

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242

Correspondence to: Dr M. Wachendorf, Department of Grass-

land Science and Renewable Plant Resources, University of

Kassel, Nordbahnhofstrasse 1A, 37213 Witzenhausen, Ger-

many.

E-mail: mwach@uni-kassel.de

Received 25 October 2004; revised 31 March 2006

This article is dedicated to Alois Kornher, retired

Professor of Grassland and Forage Production at the

University of Kiel, on his 70th birthday.

232

farming. The positive effects of nitrogen supply from

mineral fertilizer or slurry on the yield of dry matter

(DM) from maize are well documented (Schroder et al.,

1998; Nevens, 2003). At low levels of N supply, yield

responses were much higher for maize in monoculture

than for maize in a crop rotation, whereas at higher

levels, differences disappeared and response curves

levelled off (Cerrato and Blackmer, 1990; Bullock and

Bullock, 1994; Nevens and Reheul, 2001). Increased N

supply concomitantly reduced N-use efficiency and

increased N surpluses (Schroder, 1998), resulting in

increased levels of soil mineral N (SMN) in autumn

(Schroder et al., 1993). This, in turn, may increase the

risk of N losses as nitrate to the groundwater or as

ammonia and nitrous oxides to the atmosphere.

Cover crops (e.g. small grain crops and grasses) grown

with maize protect the soil from wind and water erosion

(Kaspar et al., 2001), take up N from the mineralization

of slurry after July, when the maize crop has ceased N

uptake (Pollmer et al., 1979), as well as reduce residual

SMN (Ditch et al., 1993). However, cover crops can be

detrimental if too much N is bound and not released in

a timely manner to the next crop (Vyn et al., 1999).

Karlen and Doran (1991) showed that cover crops

before sowing maize created an early-season N defici-

ency, and even additional N fertilizer did not help to

make up the difference. Considering the short time

period available for growth after the harvest of maize,

undersowing of crops in spring may be advantageous,

as they could take up more N. Difficulties may arise,

when the understorey is sown too early, resulting in an

increased competition for water, light and nutrients

with maize in the spring.

While the effects of many individual effects (e.g. N

supply from slurry, mineral-N fertilizer application and

grass understorey) on performance and N surplus in

silage maize production have been investigated, com-

paratively little is known regarding how these effects

interact to affect these parameters. The objective of the

present study was therefore to examine the influences

of various combinations of N supply from slurry and

mineral fertilizer and that of a grass understorey on the

performance and N surplus of maize production. The

work presented here is part of the Karkendamm project

at the University of Kiel (Taube and Wachendorf,

2001), started in 1997. The main objective of this

integrated research project was to assess the agronomic

and ecological impacts of a wide range of dairy farming

strategies on sandy soils in northwest continental

Europe. Plot experiments covered a wide range of

production methods on grassland (Kelm et al., 2004;

Trott et al., 2004; Wachendorf et al., 2004b) and in

arable forage production (Bobe et al., 2004; Wachendorf

et al., 2004a). This article is the first of two that deals

with the production of maize for silage. It reports on the

performance and N surplus of maize for a range of

production strategies and is based on the results of a

4-year, multifactorial field experiment, addressing the

following questions:

(i) How does N supply by cattle slurry and mineral

fertilizer affect the productivity, herbage quality

and N surplus of maize for silage? and

(ii) What is the reaction of a grass understorey to the

changes in N supply and does a grass understorey

modify the response of maize to variation in N

availability?

The second article (Wachendorf et al., 2006) reports

on the corresponding NO3-leaching losses and on the

estimates of them by means of SMN at the end of the

growing season and by N surplus data.

Materials and methods

Experimental site

The experiment was carried out on the experimental

farm ‘Karkendamm’ of the Faculty of Agricultural and

Nutritional Sciences at the University of Kiel in

northern Germany (53�55¢N, 9�55¢E; 14 m asl). The

climate is humid temperate, with mild winters and

usually sufficient summer rainfall. However, drought

periods may occur, mainly in late spring and summer.

The weather conditions during the experiment (1998–

2001) are presented in Table 1. The soil is a Gley-

Podzol, dominated by a coarse sand texture that makes

it particularly permeable. Further soil properties are

given in Table 2. The plant-available soil water at field

capacity is 144 mm to a depth of 60 cm. The ground

water table is at a depth of 1.5–2.0 m in summer and

1.0–1.5 m in winter. The slope of the experimental

site is very small. The experimental site had been

used for forage maize (40 m3 slurry ha)1; 50 kg min-

eral N ha)1) for 5 years before the establishment of the

experiment.

Table 1 Mean daily temperature, rainfall and incident radi-

ation from May to October for the experimental years (1998–

2001) and long-term mean values (1980–1999).

Mean daily

temperature

(�C)

Rainfall

(mm)

Incident

radiation

(MJ m)2)

1998 13Æ2 647Æ2 2386Æ9

1999 14Æ3 320Æ1 2712Æ1

2000 12Æ9 322Æ4 2878Æ3

2001 14Æ6 520Æ7 3129Æ0

Mean (1998–2001) 13Æ8 452Æ6 2776Æ7

Long-term mean

(1980–1999)

13Æ7 455Æ3 2593Æ3

Performance and environmental effects of forage production on sandy soils 233

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd, Grass and Forage Science, 61, 232–242

Field experiment

The treatments were compared in a split-plot design

with cattle slurry (S) as the main plot, mineral N

fertilizer (ammonia nitrate) as the subplot and grass

understorey (perennial ryegrass, Lolium perenne L.; U)

as the sub-subplot with four block replicates. The size

of sub-subplot was 255 m2 (ten rows with a length

of 17 m). The treatments used are summarized in

Table 3. The maize (variety Naxos) was sown with

10 plants m)2 at the end of April/start of May with

75 cm between the plant rows. Perennial ryegrass

(L. perenne L., variety Fennema) was sown between

the maize rows with a conventional drill at 6 kg ha)1

and 12.5 cm distance from the maize rows when the

maize had three to four leaves. The understorey was left

on the field after the harvest of maize to provide a

winter cover and was incorporated into the soil by

ploughing prior to the sowing of the next year’s maize.

Weeds were controlled chemically by herbicide appli-

cations at emergence of the maize and when the maize

had two to four leaves. Herbicides were selected on the

basis of the actual weed infestation and compatibility

with the undersown grass. Slurry was applied with a

trailing hose after ploughing the winter cover at the end

of April immediately prior to the sowing of maize, thus

volatilization losses have not been excluded completely.

The average concentrations of total N, P2O5, K2O and

MgO in the slurry were 3Æ1, 1Æ6, 6Æ6, 0Æ9 kg m)3 and

67 g kg)1 DM respectively. The N fertilizer was split into

two equal applications at two to three leaves and five to

six leaves of maize. All plots received 30 kg P ha)1 into

the seedbed and a broadcast application of another

35 kg ha)1. Potassium was applied to all variants

corresponding to the highest level of cattle slurry

application (¼264 kg K2O ha)1), which was the K

uptake of maize in previous experiments under com-

parable soil conditions at maximum N application rates.

Liming was conducted twice during the experiment in

order to maintain soil pH at 5–5Æ5. As a result of the

technical problems, no understorey was established in

1997; thus data from a 4-year period (1998–2001) are

presented in the present article.

Herbage sampling

The number of maize plants was determined by count-

ing the plants of two rows per plot. No differences

occurred because of cover crops, slurry or N fertilizer

application (data not shown). Fresh mass (FM) of maize

was determined by cutting the plants of two rows in the

centre of each plot at a stubble height of 20 cm. DM

content was determined from 500 to 600 g chopped FM

by drying at 65�C for 5 d in a forced-air oven to constant

weight. After cooling and weighing, the samples were

ground in a Cyclotec mill (Foss Tecator, Hoganas,

Sweden) to pass a 1-mm screen. The FM of the grass

understorey was determined in autumn (mid-Novem-

ber) and spring (end of April) by cutting the sward to

ground level in an area of 0Æ25 m2 in two replicates per

plot between the rows of maize. All understorey data

were corrected for the two 12Æ5 cm fallow strips along

the maize rows. Samples were weighed and dried at

65�C. At the same spot, soil samples (diameter of core

8 cm) were taken to a depth of 30 cm using a plant root

auger (Eijkelkamp Agrisearch Equipment, Giesbeek,

The Netherlands) and immediately frozen at )22�C.

After thawing, soil cores were washed carefully on a

530-lm sieve. Roots were separated manually from

organic and mineral soil particles and residues of maize

stubbles. Samples were weighed and dried at 65�C.

Chemical analyses

Crude protein and net energy (NEL) concentrations of

maize and the grass understorey were analysed by near

infrared spectroscopy (NIRS). For maize, the calibration

of CP was based on Kjeldahl N; the NEL concentration

was calculated according to Weißbach et al. (1996a,b),

based on the technique of De Boever et al. (1983).

Standard errors of prediction (SEP) for the NIRS

equations used were 4.2–6.7 g kg)1 DM for CP concen-

tration and 0.21–0.31 MJ NEL kgm)1 DM for NEL

concentration. Details are given elsewhere (Volkers

et al., 2003). The N concentration of the above- and

below-ground understorey biomass was estimated

using a NIR calibration from Kaske (2000), with

SEPs of 1Æ2 g N kg)1DM for stubbles and roots and

Table 2 Soil horizons and properties at the experimental

site (soil classification after USDA, 1998).

Horizon

Depth

(cm)

BD

(g cm)3)

PV

(%)

FC (mm

cm)1)

C

(%)

N

(%) C:N

Ap 0–28 1Æ06 50Æ8 2Æ70 7Æ47 0Æ30 24Æ7

E+Bh 28–57 1Æ43 42Æ3 2Æ15 1Æ49 0Æ07 21Æ3

Bh 57–79 1Æ62 34Æ3 1Æ61 0Æ89 0Æ04 21Æ0

Cg 79–94 1Æ65 37Æ4 1Æ71 0Æ40 0Æ02 16Æ4

BD, soil bulk density; PV, pore volume; FC, plant available soil

water at field capacity; C, total organic carbon; N, total

nitrogen; C:N, carbon:nitrogen ratio.

Table 3 Treatments used in the experiment.

Treatment Level

Cattle slurry 0, 20 and 40 m3 ha)1

Mineral N fertilizer 0, 50, 100 and 150 kg N ha)1

Grass understorey With and without perennial

ryegrass (Lolium perenne L.)

234 M. Wachendorf et al.

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242

1Æ0 g N kg)1DM for harvestable biomass of perennial

ryegrass swards.

Nitrogen recoveries

There is no common standard for the calculation of N

recoveries at the field scale. The objective was to

establish a surplus figure that was both simple to

calculate and relevant for nitrate leaching in winter (see

Wachendorf et al., 2006). N surplus was calculated for

each treatment as shown in Table 4. In order to get

information on the amount of N that is at risk of

leaching, the N output includes the N bound in the

understorey over winter. Atmospheric deposition was

estimated as 20 kg N ha)1 year)1, based on other

experiments (Wellbrock, 2002). Apparent recoveries

of fertilizer N and slurry N were calculated according to

the difference method (Schroder et al., 1997), consid-

ering the N yield both from the maize and from the

understorey:

ANRN ¼ ½N yield of fertilized maize and understorey ðkg ha�1Þ�N yield of unfertilized maize and understorey ðkg ha�1Þ��100=N supply by mineral fertilizer ðkg ha�1Þ

ANRS ¼ ½N yield of slurry-fertilized maize and understorey ðkg ha�1Þ�N yield of unfertilized maize and understorey ðkg ha�1Þ��100=N supply by slurryðkg ha�1Þ

where ANRN is the apparent recovery of fertilizer N (%)

ANRS the apparent recovery of slurry N (%).

This method is based on the assumption that the N

supply by fertilizer and slurry does not affect the

mineralization of soil organic matter and the growth

and N uptake by plant roots.

Statistics

The field experiment was a 4-year experiment, in

which treatments stayed in fixed positions so that

treatments have a cumulative nature. It can be argued

that this warrants the introduction of time as a

quantitative fixed effect in the statistical model. As a

result of the random variation of environmental

conditions from year to year, a full exploitation of

data may further need the introduction of year as a

random effect, as suggested by Hansen et al. (2000a,b).

Such a procedure would allow the interpretation of

treatment · time interactions as a systematic effect,

while treatment · year interactions would point at

differences in yield stability between years. In the

analysis of the present data, year had no strong

influence, which may be because the duration of the

experiment was over a relatively short time. Thus,

analyses of variance were performed without any year

effects, considering the split-plot structure of the trial

using the procedure MIXED in sas (SAS Institute,

1996). Data presented are LSMEANS across years

produced in the analysis. Only common standard

errors for all LSMEANS are given in tables and

diagrams. For a conservative interpretation, the high-

est value was chosen in the case of different standard

errors among treatments. To obtain a functional

description, regression analysis was performed with

the procedures NLIN and GLM in sas. The models were

selected on the basis of residual diagnostic, r2 and

residual standard deviation. The critical probability

value generally was P ¼ 0Æ05.

Results

Net energy yield of maize increased with mineral-N

application rate but reached a plateau at high rates of N

application (Figure 1, Appendix A). Increase in DM

yield of maize because of mineral-N fertilizer was lower

at higher slurry application rates. The reduction in DM

yield of maize because of the understorey was greater

with a reduced input of slurry and fertilizer N (Table 5).

There were no consistent effects of slurry, mineral N

and understorey on NEL concentration of maize (over-

all mean, 6Æ65 MJ kg)1 DM), thus patterns of yield of

NEL are similar to those of DM yield (data not shown).

Mean NEL and DM yields ranged from 39 GJ ha)1 and

6 t ha)1 (S 0 and N 0, with understorey) to 102 GJ ha)1

and 15 t ha)1 (S 20 and N 150, without understorey)

respectively.

Crude protein concentration increased by an average

of 0Æ25 g kg)1 DM with each additional cubic metre of

slurry and with each additional kilogram of fertilizer N

(Figure 2). CP concentration varied between 50 g kg)1

DM (S 0 and N 0, with understorey) and 78 g kg)1 DM

(S 40 and N 150, with understorey) and there was no

significant effect of the grass understorey (Table 5).

Regression analysis revealed that with 40 m3 slurry

ha)1 CP concentration levelled off at high application

rates of fertilizer-N, whereas the increase in CP

concentration was linear over the whole range of

fertilizer-N application at lower rates of slurry applica-

tion.

Although an exponential function produced a better

fit to the measured N yields, a clear asymptotic response

of N yield to the amount of mineral-N fertilizer applied

Table 4 Input and output components included in the

calculation of N recovery.

N input N output

Mineral fertilizer N + slurry

N + atmospheric deposition

N yield of silage

maize + grass N

N recovery ¼ N input ) N output.

Performance and environmental effects of forage production on sandy soils 235

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd, Grass and Forage Science, 61, 232–242

was only detected for the highest rate of slurry

application (S 40) (Figure 3). The N yield of the

unfertilized control was 60 kg ha)1 with little variation

among years, indicating a persisting release of N from

the soil organic matter. Across all treatments, under-

storey reduced the N yield of maize by only 6 kg ha)1

(understorey only significant as a main effect, see

Table 5). Mean fertilizer-N recovery in treatments

without slurry was proportionately 1Æ5 and 0Æ9 with

and without understorey respectively. With decreasing

fertilizer-N supply, the increase in N recovery with

understorey was more pronounced than without

understorey (significant U · N interaction). In treat-

ments without mineral N, apparent recovery of slurry N

was proportionately 0Æ8 at 20 m3 ha)1 and 0Æ5 at

40 m3 ha)1, respectively, when no grass crop was

undersown. An understorey significantly increased N

recovery to 1Æ8 and 1Æ1 proportionately (with a minor

U · slurry interaction).

The biomass of the undersown grass (including above-

ground and root biomass) ranged from 2Æ7 to 4Æ7 t

organic matter ha)1 (Figure 4). Understorey biomass

significantly decreased with increase in rate of mineral-

N fertilizer application and slurry application both in

autumn and in spring (Table 6). In contrast, N concen-

tration in the understorey ranged from 13 to 20 g kg)1

DM and increased with increase in rate of mineral-

N fertilizer application and with slurry application at both

sampling seasons. The total amount of N in the under-

storey ranged from 50 to 68 kg ha)1 and decreased with

increase in rate of mineral-N fertilizer application in

spring. No significant effect of fertilizer could be detected

in autumn. The total N yield of understorey was not

affected by the slurry application rate.

Mineral N fertilizer (kg ha–1) Mineral N fertilizer (kg ha–1)

0 50 100 150

Net

ene

rgy

yiel

d (G

J ha

–1)

Net

ene

rgy

yiel

d (G

J ha

–1)

0

40

50

60

70

80

90

100

0 50 100 1500

40

50

60

70

80

90

(a) (b)100

Figure 1 Net energy yield (GJ ha)1) of

maize for silage as affected by mineral N

fertilizer (kg ha)1) and slurry application

rate (d ———, ¤ – – – and m - - - - are

0, 20 and 40 m3 slurry ha)1, respectively)

without (a) and with (b) grass understo-

rey. Average of 4 years. Regression lines

were fitted separately for each slurry level;

regression statistics see Appendix A.

Vertical bars indicate the common stand-

ard error of means for each plot.

Table 5 F values and levels of significance of ANOVAANOVA for the effects of understorey (U), application of slurry (S) and application

of mineral N (N) on net energy yield, crude protein (CP) concentration, N yield and N recovery of silage maize (average of 4 years).

Effect

Net energy yield CP concentration N yield N recovery

F value

Level of

significance F value

Level of

significance F value

Level of

significance F value

Level of

significance

U 45Æ6 <0Æ0001 1Æ52 0Æ2219 17Æ93 <0Æ0001 756Æ43 <0Æ0001

S 61Æ20 0Æ0010 71Æ41 <0Æ0001 68Æ03 <0Æ0001 213Æ99 <0Æ0001

N 541Æ25 <0Æ0001 218Æ79 <0Æ0001 563Æ63 <0Æ0001 234Æ94 <0Æ0001

S · N 45Æ53 <0Æ0001 2Æ12 0Æ0631 9Æ65 <0Æ0001 1Æ1 0Æ3383

U · S 5Æ49 0Æ0062 0Æ45 0Æ6368 1Æ38 0Æ2581 1Æ93 0Æ1345

U · N 1Æ71 0Æ1725 1Æ42 0Æ2461 2Æ00 0Æ1213 7Æ03 <0Æ0001

U · S · N 2Æ54 0Æ0281 0Æ48 0Æ8223 0Æ83 0Æ5533 0Æ45 0Æ8436

236 M. Wachendorf et al.

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242

If N yield of maize is considered as the only output

variable, ANOVAANOVA results for N surplus showed the

same significances (data not shown) as occurred

with N yield. Although the understorey biomass was

not removed from the field, the amount of N bound in

the understorey is biologically conserved over winter,

and thus is not prone to leaching. Consequently, the

corresponding amount of N present in the biomass in

spring was considered as an output in the surplus

calculation. Common exponential regressions were

fitted separately to the data of treatments with and

without understorey respectively (Figure 5).

y�U ¼ �80�2192þ 40 �1882e0�0054x ;

s.e. of estimate ¼ 10�97; r2 ¼ 0�94;

P < 0�0001;n ¼ 12 and

yþU ¼ �110�3183þ 27�5318e0�0064x ;

s.e. of estimate ¼ 9�45; r2 ¼ 0�95;

P < 0�0001; n ¼ 12;

where y-U/+U is the N surplus (kg ha)1) under silage

maize without/with understorey and x the annual N

input (kg ha)1).

Mineral N fertilizer (kg ha–1) Mineral N fertilizer (kg ha–1)

Cru

de p

rote

in c

once

ntra

tion

(g k

g–1 D

M)

Cru

de p

rote

in c

once

ntra

tion

(g k

g–1 D

M)

0 50 100 150 0 50 100 1500

40

50

60

70

80

0

40

50

60

70

80(a) (b)

Figure 2 Crude protein concentration

of maize for silage as affected by mineral N

fertilizer (kg ha)1) and slurry application

rate (d ———, r – – – and m - - - - are

0, 20 and 40 m3 slurry ha)1, respectively)

without (a) and with (b) grass understo-

rey. Average of 4 years. Regression lines

were fitted separately for each slurry level;

regression statistics see Appendix A.

Vertical bars indicate the common

standard error of means for each plot.

0 50 100 1500

30

60

90

120

150

180

0 50 100 1500

30

60

90

120

150

180

Mineral N fertilizer (kg ha–1) Mineral N fertilizer (kg ha–1)

N y

ield

(kg

ha–1

)

N y

ield

(kg

ha–1

)

(a) (b)

Figure 3 Nitrogen yield (kg ha)1) of

maize for silage as affected by mineral N

fertilizer (kg ha)1) and slurry application

rate (d ———, r – – – and m - - - - are

0, 20 and 40 m3 slurry ha)1, respectively)

without (a) and with (b) grass understo-

rey. Average of 4 years. Regression lines

were fitted separately for each slurry level;

for statistics see Appendix A. Vertical bars

indicate the common standard error of

means for each plot.

Performance and environmental effects of forage production on sandy soils 237

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd, Grass and Forage Science, 61, 232–242

The curves for N surplus of maize were nearly parallel

over the whole range of annual N input with a

difference of 80 kg N ha)1 at low levels of N input

and 70 kg N ha)1 at high levels. Values ranged from –

80 kg N ha)1 with understorey to 120 kg N ha)1 with-

out understorey.

Discussion

Total requirements of nitrogen fertilizer for the produc-

tion of maize for silage are approximately 150–

200 kg N ha)1. This recommendation is then adjusted

based on previous crop and manure N credits. Cox et al.

(1993) reported maximum economic yields at N rates of

140–160 kg N ha)1. In regions of Germany with

favourable soil and climatic conditions, optimum total

DM and maize DM yields were frequently obtained

with N rates of only 60–120 kg N ha)1 (Aufhammer

et al., 1996). Herrmann et al. (2004a) used the concept

of critical N concentration to determine the minimum N

concentration required for maximum crop growth rate.

From these calculations, including data from the pre-

sent experiment and other sites in Germany (resulting

in a total of twenty sites and year combinations), an

optimum total N input of 100–180 kg ha)1 was

obtained (Herrmann et al., 2004b). The current fertilizer

strategy in farming practice for silage maize on sandy

soils in northern Germany consists of 34 m3 slurry ha)1

prior to the sowing of maize and 53 kg mineral N ha)1

at sowing (Anonymous, 2002), which results in a total

estimated N input of 120–190 kg N ha)1. Although

these figures are somewhat higher than those calcula-

ted from the economic optimum, the corresponding N

surpluses at this level of N input in the present

experiment are well below 40 kg N ha)1.

N supply by slurry or mineral fertilizer, and under-

storey, did not affect NEL concentration in maize. This

is in agreement with a constant contribution of crops,

representing 0Æ65 of the maize DM across all treatments

(K.C. Volkers, unpublished data). CP concentration

increased with increase in N supply by slurry or mineral

fertilizer. With the current N rate in farming practice

(120–190 kg N ha)1; Anonymous, 2002), the CP con-

centration of the maize would be approximately

70 g kg)1, which is in the targeted range for its use in

combination with high-protein forages, like grasses or

forage legumes.

It is remarkable that N supply by slurry or mineral

fertilizer had no effects on the amount of N in the

above- and below-ground biomass of the grass under-

storey after the harvest of maize. The average of grass-

bound N was 60 kg N ha)1. Reduced understorey

biomass because of enhanced maize competition was

compensated for by an increased CP concentration in

the understorey. Competition for light presumably

played a major role. The leaf area index of unfertilized

maize at harvest was only 2Æ5 when compared with

4Æ0 at the highest levels of N supply (K.C. Volkers,

0 50 100 15002

3

4

5

0 50 100 1500

40

50

60

70

0 50 100 1500

12

14

16

18

20

22

To

latM

O(t

MO

ah1–)

Nc

cnone

rtat

ion

(gkg

1–M

D)

To

latib

mosas

N(k

gah

1–)

Mineral N fertilizer (kg N ha–1)

0 50 100 15002

3

4

5Autumn Spring

0 50 100 1500

40

50

60

70

0 50 100 1500

12

14

16

18

20

22

Figure 4 Total organic matter (top, t DM ha)1), N concen-

tration (middle; g kg)1 DM) and total biomass N (bottom;

kg ha)1) of grass understorey in autumn (left) and spring (right)

as affected by mineral N fertilizer (kg ha)1) and slurry

application rate (d ———, r – – – and m - - - - are 0, 20 and

40 m3 slurry ha)1 respectively. Average of 4 years. Vertical

bars indicate the common standard error of means for each

plot.

238 M. Wachendorf et al.

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242

unpublished data), allowing extensive light penetration

between the plant rows particularly at more mature

stages of maize, when maize leaves start to senesce and

water supply increases because of increased rainfall in

autumn. Except for the control treatment (no slurry and

fertilizer N application), no negative effect on NEL yield

of the maize could be detected. Apparently, possible

competitive effects for water and nutrients by the grass

crop over the growing season were compensated for by

the contribution of nutrients when the understorey was

incorporated into the soil in spring. There are contra-

dictory findings on the benefits of cover crops, ranging

from positive effects on maize yield to a yield reduction

(Wyland et al., 1995; Schroder et al., 1996; Scott et al.,

1987). The possible determining factor for these differ-

ences was the differing C/N ratios of the cover crops.

While the ratio for roots of grasses is in the region of 40

(Reeves et al., 1993), cover crops like the present grass

understorey, which are vegetative throughout the

annual cycle, can be assumed to be in the range of

10–30 (Thorup-Kristensen, 1994; Schroder et al., 1996),

and thus can be easily mineralized to NH4 and NO3 in

the soil. Results from Laurent and Mary (1992) and

Bollero and Bullock (1994) showed a positive relation-

ship between C/N ratio and biomass and N yield of the

cover crop respectively. However, the amount of N

conserved in the cover crop over winter and N delivery

in the following growing season was negatively corre-

lated (Schroder et al., 1996). In the present study,

perennial ryegrass was chosen among many possible

grass species, as it produces only infertile tillers in the

establishment year, resulting in a reduced competition

against maize and no undesired seed production.

Approximately, half of the understorey biomass incor-

porated into the soil in spring was aboveground veget-

ative material with a low C/N ratio, thus it is likely that a

considerable amount of N was directly available for the

maize. The impact of the grass understorey on SMN at

the end of the growing season and on NO3 leaching in

the following winter will be reported in the next article

of the series (Wachendorf et al., 2006).

When compared with leaching losses under grassland

at the same site (Trott et al., 2004; Wachendorf et al.,

2004b), maize in monoculture proved an N-efficient

crop with high N recoveries at low to moderate levels of

N supply. However, experiments with a duration

similar to the one reported here cannot be expected to

detect the longer term changes in nutrient flows that

result from small but persistent changes in the storage

Table 6 F values and levels of significance of anova for the effects of application of slurry (S) and mineral N (N) on total organic

matter (OM), N concentration and total biomass N of undersown perennial ryegrass in autumn and spring (average of 4 years).

Effect

Total OM concentration N concentration Total biomass N

F value Level of significance F value Level of significance F value Level of significance

Autumn

S 5Æ41 0Æ0118 5Æ06 0Æ3000 2Æ62 0Æ1006

N 12Æ48 0Æ0001 26Æ35 0Æ0001 1Æ50 0Æ2324

S · N 0Æ68 0Æ6660 0Æ61 0Æ7229 1Æ30 0Æ2826

Spring

S 2Æ29 0Æ1161 0Æ70 0Æ5115 1Æ87 0Æ1902

N 4Æ32 0Æ0100 4Æ02 0Æ0152 5Æ07 0Æ0054

S · N 0Æ77 0Æ5984 1Æ02 0Æ4287 1Æ76 0Æ1392

Annual N input (kg ha–1)

0 100 200 300

pN

rusu

g

lk (

as

h1–)

–120

–80

–40

0

40

80

120

Figure 5 Relationship between N surplus (kg ha)1) of maize

for silage (including grass N) and annual N input (including N

form slurry, mineral fertilizer and atmospheric deposition;

kg ha)1) grown without (– – –) and with (———) a grass

understorey. Regression equations are given in the text.

Average of 4 years. Vertical bars indicate the common standard

error of means (s, d; r, e and m, n are 0, 20 and

40 m3 slurry ha)1, respectively).

Performance and environmental effects of forage production on sandy soils 239

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd, Grass and Forage Science, 61, 232–242

of N in the soil. Likewise, such experiments do not

consider that nutrient fluxes in crop production directly

or indirectly affect all components of a farming system

(e.g. animal housing and manure storage). Thus, it is

only with whole farm-orientated models [e.g. Integra-

ted Farm System Model (IFSM); Rotz et al., 1999; Rotz

and Coiner, 2003] that comparisons between different

forage production strategies are feasible with regard to

the longer term impact on nutrient cycling within a

whole farming system. Simulations with IFSM using

data on grassland and maize from the present study

showed that extrapolation of N cycling data measured

on the Karkendamm farm to whole farm systems is

feasible (Rotz et al., 2004).

Acknowledgments

We gratefully acknowledge the financial support by the

Ministry of Environment, Nature and Agriculture of

the Schleswig-Holstein state and by the foundation

‘Schleswig-Holsteinische Landschaft’.

References

ANONYMOUSNO NY MOUS (2002) Dairy Cattle Report, 2001. Results

from the Advisory Service for Dairy Cattles in Schleswig-

Holstein (in German). Betriebswirtschaftliche Mitteilungen

No. 554/555. Kiel, Germany: Landwirtschaftskammer

Schleswig-Holstein.

Aufhammer W., Kubler E. and Kaul H.P. (1996)

Investigations on the adjustment of nitrogen supply

from different N sources to the N uptake of maize (in

German). Journal of Plant Nutrition and Soil Science, 159,

471–478.

Bobe J., Wachendorf M., Buchter M. and Taube F. (2004)

Nitrate concentration in the leachate and in the shallow

groundwater under a forage crop rotation. Grassland

Science in Europe, 9, 346–348.

Bollero G.A. and Bullock D.G. (1994) Cover cropping

systems for the central corn belt. Journal of Production

Agriculture, 7, 55–58.

Bullock D.G. and Bullock D.S. (1994) Quadratic and

quadratic-plus-plateau models for predicting optimal

nitrogen rate of corn: a comparison. Agronomy Journal,

86, 191–195.

Cerrato M.E. and Blackmer A.M. (1990) Comparison of

models for describing corn yield responses to nitrogen

fertilizer. Agronomy Journal, 82, 138–143.

Cox W.J., Kalonge S., Cherney D.J.R. and Reid W.S. (1993)

Growth, yield and quality of forage maize under different

nitrogen management practices. Agronomy Journal, 85,

341–347.

De Boever J.L., Nuyts J., De Brabander D.L., Cottyn B.G.,

Vanacker J.M. and Buysse F.X. (1983) Comparaison de la

digestibilite et du rendement de quelques varietes de

mais [Comparison of the digestibility and yield of several

varieties of maize]. Revue de L’ Agriculture (Brussels), 36,

1683–1690.

Ditch D.C., Alley M.M., Kelley K.R. and Lei Y.Z. (1993)

Effectiveness of winter rye for accumulating residual

fertilizer N following corn. Journal of Soil and Water

Conservation, 48, 125–132.

Hansen E.M., Djurhuus J. and Kristensen K. (2000a) Nitrate

leaching as affected by introduction or discontinuation of

cover crop use. Journal of Environmental Quality, 29,

1110–1116.

Hansen E.M., Kristensen K. and Djurhuus J. (2000b) Yield

parameters as affected by introduction or discontinuation

of catch crop use. Agronomy Journal, 92, 909–914.

Herrmann A., Jovanovic N. and Taube F. (2004a) The range

of the critical nitrogen dilution curve for maize (Zea mays

L.) can be extended until silage maturity. Agronomy

Journal, 96, 1131–1138.

Herrmann A., Jovanovic N. and Taube F. (2004b) Nitrogen

concentration at maturity – an indicator of N status in

forage maize production. Agronomy Journal, 97, 201–210.

Kaske A. (2000) Performance of legume/grass mixtures in arable

cropping systems and effects on yield and nitrogen budget of a

succeeding winter wheat crop. Ph.D. thesis, Kiel, Germany:

Christian-Albrechts-University.

Kaspar T.C., Radke J.K. and Laflen J.M. (2001) Small grain

cover crops and wheel traffic effects on infiltration,

runoff and erosion. Journal of Soil and Water Conservation,

54, 693–704.

Karlen D.L. and Doran J.W. (1991) Cover crop

management effects on soybean and corn growth and

nitrogen dynamics in an on-farm study. American Journal

of Alternative Agriculture, 6, 71–82.

Kelm M.R., Wachendorf M., Trott T., Volkers K.C. and

Taube F. (2004) Performance and environmental effects

of forage production on sandy soils. III. Energy efficiency

in forage production from grassland and maize for silage.

Grass and Forage Science, 59, 69–79.

Laurent F. and Mary B. (1992) Management of nitrogen in

farming systems and the prevention of nitrate leaching.

Aspects of Applied Biology, 30, 45–61.

Nevens F. (2003) Nitrogen use efficiency in grassland, silage

maize and ley/arable rotations. Ph.D. thesis, Belgium:

University of Gent.

Nevens F. and Reheul D. (2001) Crop rotation versus

monoculture: yield, N yield and ear fraction of silage

maize at different levels of mineral N fertilization.

Netherlands Journal of Agricultural Science, 49, 405–425.

Pollmer W.G., Eberhard D., Klein D. and Dhillon B.S.

(1979) Genetic control of nitrogen uptake and

translocation in maize. Crop Science, 19, 82–86.

Reeves D.W., Wood C.W. and Touchton J.T. (1993) Timing

nitrogen applications for corn in a winter legume

conservation-tillage system. Agronomy Journal, 85, 98–

106.

Rotz C.A. and Coiner C.U. (2003) Integrated Farm System

Model, Reference Manual. http://pswmru.arsup.psu.edu

(last accessed March 2004).

Rotz C.A., Satter L.D., Mertens D.R. and Muck R.E. (1999)

Feeding strategy, nitrogen cycling, and profitability of

dairy farms. Journal of Dairy Science, 82, 2841–2855.

Rotz C.A., Taube F., Russelle M., Oenema J., Sanderson

M.A. and Wachendorf M. (2004) Whole-farm

240 M. Wachendorf et al.

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242

perspectives of nutrient flows in grassland agriculture.

Crop Science, 45, 2139–2159.

SAS Institute. (1996) SAS/STAT User’s Guide, Release 6.12.

Cary, NC, USA: SAS Institute Inc.

Schroder J.J. (1998) Towards improved nitrogen management

in silage maize production on sandy soils. Ph.D. thesis, The

Netherlands: University of Wageningen.

Schroder J.J., Ten Holte L., Van Keulen H. and Steenvor-

den J.H.A.M. (1993) Effects of nitrification inhibitors and

time and rate of slurry and fertiliser N application on

silage maize yield and losses to the environment. Fertilizer

Research, 34, 267–277.

Schroder J.J., Van Dijk W. and De Groot W.J.M. (1996)

Effects of cover crops on the nitrogen fluxes in a silage

maize production system. Netherlands Journal of

Agricultural Science, 44, 293–315.

Schroder J.J., Ten Holte L. and Brouwer G. (1997)

Response of silage maize to placement of cattle slurry.

Netherlands Journal of Agricultural Science, 45, 249–261.

Schroder J.J., Neeteson J.J., Withagen J.C.M. and Noij

I.G.A.M. (1998) Effects of N application on agronomic

and environmental parameters in silage maize

production on sandy soils. Field Crops Research, 58, 55–67.

Scott T.W., Pleasant J.M., Burt R.F. and Otis D.J. (1987)

Contributions of ground cover, dry matter and nitrogen

from intercrops and cover crops in a corn polyculture

system. Agronomy Journal, 79, 792–798.

Taube F. and Wachendorf M. (2001) The nitrogen project: a

systems approach to optimise nitrogen use efficiency on

the dairy farm. In: Proceedings of the American Forage and

Grassland Council, Vol. 10. Springdale, AR, USA:

American Forage and Grassland Council, pp. 223–228.

Thorup-Kristensen K. (1994) The effect of nitrogen catch

crop species on the nitrogen nutrition of succeeding

crops. Fertilizer Research, 37, 227–234.

Trott H., Wachendorf M., Ingwersen B. and Taube F.

(2004) Performance and environmental effects of forage

production on sandy soils. I. Impact of defoliation system

and nitrogen input on performance and N surplus of

grassland. Grass and Forage Science, 59, 41–55.

USDA. (1998) Keys to soil taxonomy. 8th edn. Washington

DC, USA: USDA.

Volkers K.C., Wachendorf M., Loges R., Jovanovic N.J.

and Taube F. (2003) Prediction of the quality of forage

maize by near-infrared reflectance spectroscopy. Animal

Feed Science and Technology, 109, 183–194.

Vyn T.J., Janovicek K.J., Miller M.H. and Beauchamps E.G.

(1999) Soil nitrate accumulation and corn response to

preceding small-grain fertilization and cover crops.

Agronomy Journal, 91, 17–24.

Wachendorf M., Volkers K. and Taube F. (2004a) Forage

production in a crop rotation: effects on performance and

N surplus. Grassland Science in Europe, 9, 753–757.

Wachendorf M., Buchter M., Trott H. and Taube F.

(2004b) Performance and environmental effects of forage

production on sandy soils. II. Impact of defoliation

system and nitrogen input on nitrate leaching losses.

Grass and Forage Science, 59, 56–68.

Wachendorf M., Buchter B., Volkers K.C., Bobe J., Loges

R. and Taube F. (2006) Performance and environmental

effects of forage production on sandy soils. V. Impact of

grass understorey, slurry application and mineral N

fertilizer on nitrate leaching under maize for silage. Grass

and Forage Science, 61, 243–252.

Weißbach F., Kuhla S. and Schmidt L. (1996a) Estimation of

the metabolizable energy in forages by a cellulase-method.

Proceedings of the Society of Nutrition Physiology, 5, 115.

Weißbach F., Kuhla S. and Schmidt L. (1996b) Simplified

method for calculation of NEL from metabolizable

energy. Proceedings of the Society of Nutrition Physiology, 5,

117.

Wellbrock N. (2002) Assessment and changes of the

atmospherical deposition – transfer of results from a

beech wood to other woodland ecosystems in Schleswig-

Holstein (in German). EcoSys – Beitrage zur

Okosystemforschung, 35, 1–180.

Wilkinson J.M., Newman G. and Allen D.M. (1998) Maize –

producing and feeding maize silage. Lincoln, UK: Chalcombe

Publications.

Wyland L.J., Jackson L.E. and Schulbach K.F. (1995)

Soil-plant nitrogen dynamics following incorporation

of a mature rye cover crop in a lettuce production

system. Journal of Agricultural Science, Cambridge, 124,

17–25.

Performance and environmental effects of forage production on sandy soils 241

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd, Grass and Forage Science, 61, 232–242

Appendix A

Table A1 Coefficients of regression models, r2 values, standard errors and levels of significance for net energy yield (GJ NEL ha)1),

crude protein concentration (g kg)1 DM) and N yield (kg ha)1) of silage maize as affected by mineral N fertilizer (kg ha)1) with and

without understorey at different rates of slurry application (average of 4 years).

Dependent variable Understorey

Slurry

(m3 ha)1) m a b c r2 s.e.

Level of

significance

NEL yield (GJ NEL ha)1) With 0 107Æ6488 4Æ2010 0Æ0096 – 0Æ96 4Æ2 <0Æ0001

y ¼ m ) e(a ) bN) 20 96Æ4361 3Æ4312 0Æ0208 – 0Æ94 3Æ3 <0Æ0001

40 96Æ4558 2Æ8210 0Æ0145 – 0Æ66 4Æ4 0Æ0009

Without 0 96Æ9 3Æ9276 0Æ0175 – 0Æ97 3Æ54 <0Æ0001

20 104Æ5 3Æ3558 0Æ0089 – 0Æ83 3Æ93 <0Æ0001

40 97Æ3 2Æ9714 0Æ0147 – 0Æ80 3Æ6 <0Æ0001

CP concentration (g kg)1) With 0 – 49Æ4625 0Æ1296 – 0Æ97 1Æ50 0Æ0105

y ¼ a + bN + cN2 20 – 55Æ2331 0Æ1411 – 0Æ99 0Æ80 0Æ0026

40 – 58Æ2453 0Æ2296 –0Æ0008 0Æ99 0Æ51 0Æ0390

Without 0 – 45Æ4862 0Æ1672 – 0Æ99 0Æ82 0Æ0019

20 – 53Æ7594 0Æ1457 – 0Æ99 0Æ66 0Æ0016

40 – 57Æ6141 0Æ2108 –0Æ0006 0Æ99 0Æ78 0Æ0532

N yield (kg ha)1) With 0 458Æ5575 6Æ0194 0Æ0020 – 0Æ97 7Æ6 <0Æ0001

y ¼ m ) e(a ) bN) 20 219Æ9678 4Æ9206 0Æ0074 – 0Æ93 10Æ1 <0Æ0001

40 196Æ4428 4Æ4427 0Æ0092 – 0Æ92 7Æ6 <0Æ0001

Without 0 239Æ93 5Æ2205 0Æ0059 – 0Æ96 8Æ8 <0Æ0001

20 229Æ4 4Æ8734 0Æ0059 – 0Æ89 10Æ9 <0Æ0001

40 189Æ5 4Æ3572 0Æ0114 – 0Æ88 9Æ4 <0Æ0001

s.d., residual standard deviation.

242 M. Wachendorf et al.

� 2006 The Authors

Journal Compilation � 2006 Blackwell Publishing Ltd. Grass and Forage Science, 61, 232–242