Yield, N uptake and N-use efficiency of and N leaching after oilseed rape grown in different crop management systems in northern Germany

Klaus Sieling and Olaf Christen

Institute of Crop Science and Plant Breeding, Christian-Albrechts-University, 24118 Kiel, Germany

sieling@pflanzenbau.uni-kiel.de

christen@pflanzenbau.uni-kiel.de

Abstract

Within a winter oilseed rape – winter wheat – winter barley rotation, the effects of tillage (minimum tillage, conventional tillage), mineral N fertilization (0, 120, 240 kg N ha^-1), application of pig slurry (none, 80 kg N ha^-1 in autumn, 80 kg N ha^-1 in spring, 80 kg N ha^-1 in autumn plus in spring) and fungicides (none, fungicides in autumn, in early spring and at flowering) on yield, N uptake and N-use efficiency and N leaching were tested during 1990/91-1996/97. Mineral fertilizer N increased the seed yield and the N uptake by the seeds of oilseed rape more than slurry N. Spring slurry led to higher seed yield and N uptake compared with autumn slurry N. The effect of fungicide application was higher, if mineral N was applied. At low mineral N fertilization, minimum tillage reduced the seed yield, while at higher N levels, no differences occurred between the tillage treatments. Increasing mineral N fertilization from 120 up to 240 kg N ha^-1 decreased the apparent use efficiency of mineral fertilizer N (calculated by the difference method) from 37 to 29 %. The effect of slurry remained small, while fungicide application improved the N utilization. Due to the smaller N uptake in the unfertilized plots, minimum tillage led to a higher mineral N-use efficiency. Spring slurry N (28 %) was better used by the seeds than autumn slurry N (15 %). Application of 120 kg mineral N ha^-1 increased the slurry N utilization in all slurry treatments compared with 0 or 240 kg mineral N ha^‑1. Due to the early development of oilseed rape in combination with the late beginning of the net N mineralization in northern Germany, mineral N fertilization led to vigour plants which used the available N more efficiently. In autumn, oilseed rape can take up a lot of N and prevent it from leaching. But after harvest, large amounts of mineral N remain in the soil, which can be used only to a small extent by the following wheat. The effect of mineral N fertilization alone on N leaching was negligible, whereas slurry application increased N losses during the following percolation period.

Keywords: Tillage, autumn slurry, spring slurry, mineral N, fungicide

Introduction

In the last decades, the public interest about the environmental aspects of the crop production has increased considerably. In consequence, the crop husbandry should be improved in order to increase the profitability and to minimize the negative effects on the environment. Especially an intensive N fertilization is often regarded to increase leaching (Sieling et al. 1997). However, information about the effects of different cropping systems on the yield, N uptake by the seeds and the slurry and mineral N-use efficiency of oilseed rape as well as the N leaching are scarce. Due to its ability to take up substantial quantities of nitrogen before winter (Barraclough 1989), oilseed rape is regarded as a suitable crop to utilize autumn slurry and to prevent slurry nitrogen from leaching during the percolation period. In autumn 1990, a field trial was set up with a winter oilseed rape (cv. Falcon) – winter wheat (cv. Orestis)– winter barley (cv. Alpaca) rotation. Following factors were tested:

- Tillage: Minimum tillage without ploughing, conventional tillage using a plough

- Pig slurry: None, 80 kg N ha^-1 in autumn, 80 kg N ha^-1 in spring, 80 kg N ha^-1 in autumn + in spring

- Mineral N fertilization: 0/0/0, 40/40/40, 80/80/80 kg N ha^-1

- Fungicide application: None, fungicides in autumn, early spring and flowering

Seed Yield of oilseed rape

In average of the years 1991-96 and all other factors, mineral N fertilization significantly increased the seed yield from 2,35 t DM ha^-1 in the mineral N unfertilized treatment to 3,27 t DM ha^-1 in the 120 kg N ha^-1 treatment (Tab. 1). The yield maximum with 3,64 t DM N ha^-1 was observed in the 240 kg N ha^-1 treatment. Slurry also increased the seed yield, but the effect was smaller than for mineral N. The comparison of the application dates showed a higher increase after spring slurry than after autumn slurry. Without any N supply, oilseed rape yielded 1,90 t DM ha^-1. The slurry by mineral N interaction was negative, indicating that the effect of slurry decreased with increasing mineral N fertilization. In average, conventional tillage using a plough followed by a harrow-drilling combination significantly outyielded the minimum tillage by 0.11 t DM ha^-1. The differences were highest in the mineral N unfertilized plots and disappeared, if 240 kg N ha^-1 were applied. The application of fungicides significantly increased seed yield from 2.81 to 3,07 t DM ha^-1. The effect was more pronounced in combination with mineral N fertilization.

Table 1:   Effect of tillage, fungicides, slurry and mineral N fertilization on the average yield (t DM ha^-1) of oilseed rape at Hohenschulen Experimental Station (Kiel, Germany) (1991-1996)

	Mineral N fertilization (kg N ha^-1)
	0/0/0	40/40/40	80/80/80	Mean
Tillage
Minimum tillage	2,25	3,25	3,64	2,88^b
Conventional tillage	2,46	3,30	3,64	2,99^a
Slurry application (80 kg N ha^-1)
None	1,90	2,89	3,45	2,72^d
Autumn	2,14	3,27	3,69	2,82^c
Spring	2,49	3,33	3,69	3,00^b
Autumn + Spring	2,70	3,59	3,72	3,18^a
Fungicides in autumn, early spring and at flowering
No	2,28	3,08	3,45	2,81^b
Yes	2,41	3,46	3,82	3,07^a
Mean	2,35^c	3,27^b	3,64^a

Table 2:   Effect of tillage, fungicides, slurry and mineral N fertilization on the average N uptake by the seeds (kg N ha^-1) of oilseed rape at Hohenschulen Experimental Station (Kiel, Germany) (1991-1996)

	Mineral N fertilization (kg N ha^-1)
	0/0/0	40/40/40	80/80/80	Mean
Tillage
Minimum tillage	61	100	126	89^b
Conventional tillage	70	102	128	94^a
Slurry application (80 kg N ha^-1)
None	51	82	115	82^d
Autumn	58	100	126	86^c
Spring	70	108	134	96^b
Autumn + Spring	77	115	133	101^a
Fungicides in autumn, early spring and at flowering
No	63	96	121	87^b
Yes	67	107	134	96^a
Mean	65^c	101^b	127^a

N uptake by the seeds of oilseed rape

In general, the N uptake by the seeds showed a similar pattern as the seed yield (Tab. 2). Both mineral N fertilization and slurry application increased the N uptake. The effect of mineral N was higher than that of slurry. Without any N fertilization, oilseed rape took up 51 kg N ha^-1 by the seeds. Highest values were observed in the combination of (autumn slurry plus) spring slurry and 240 kg N ha^-1 with more than 130 kg N ha^-1. However, the comparison of the N uptake by the seeds with the N supply revealed that the simple N balance (mineral N plus slurry N minus N uptake by the seeds) was negative only in the unfertilized control. In all other cases, a N surplus occurred which varied between +10 kg N ha^-1 in the spring slurry treatment without mineral N and more than 250 kg N ha^-1 in the plots with the highest supply.

apparent N-use efficiency (NUE)

The apparent N-use efficiency for mineral fertilizer N (FNUE) was calculated by comparing the uptake of a fertilized plot with the uptake of the corresponding unfertilized plot with the same slurry treatment in relation to the amount of applied N, whereas the apparent N-use efficiency for slurry N (SNUE) was calculated by comparing the uptake of a slurry treated plot with the corresponding non-slurry treated plot with the same mineral N treatment in relation to the amount of applied N.

In average, oilseed rape utilized 37 % in the 120 kg N ha^-1 treatment and 29 % of the mineral fertilizer N in the 240 kg N ha^-1 plots (Tab. 3). Slurry application only slightly affected FNUE. Due to the smaller N uptake in the mineral unfertilized plots, FNUE was higher after minimum tillage than after conventional tillage. Fungicide application increased FNUE significantly. In experiments with labelled ¹⁵N Chalmers & Darby (1992) observed a recovery of 17 to 35 % of the fertilizer-derived N in the seed of oilseed rape.

Table 3:   Effect of tillage, fungicides, slurry and mineral N fertilization on the average mineral N use efficiency (%) of oilseed rape at Hohenschulen Experimental Station (Kiel, Germany) (1991-1996)

	Mineral N fertilization (kg N ha^-1)
	0/0/0	40/40/40	80/80/80	Mean
Tillage
Minimum tillage	-	40	30	35^a
Conventional tillage	-	34	27	30^b
Slurry application (80 kg N ha^-1)
None	-	32	30	31^a
Autumn	-	41	31	36^a
Spring	-	36	28	32^a
Autumn + Spring	-	39	26	32^a
Fungicides in autumn, early spring and at flowering
No	-	33	27	30^b
Yes	-	42	31	36^a
Mean	-	37^a	29^b

Oilseed rape utilized spring slurry N (28 %) to a greater extent than autumn slurry N (15 %), but SNUE remained low compared with mineral fertilizer N (Table 4). Despite the higher N amount, the combined slurry application in autumn + spring only increased N uptake to the same extent as spring slurry alone (Table 2). Therefore, the NUE of autumn + spring slurry N was decreased. NUE differed significantly between the mineral N treatments. The availability of spring slurry N is low presumably because the soil microflora prefers the ammonium form and competes for it with the plants (Recous et al. 1992). In addition, the ammonium fraction must be converted into nitrate before it is taken up by the plant.

Table 4:   Effect of tillage, fungicides, slurry and mineral N fertilization on the average slurry N use efficiency (%) of oilseed rape at Hohenschulen Experimental Station (Kiel, Germany) (1991-1996)

	Mineral N fertilization (kg N ha^-1)
	0/0/0	40/40/40	80/80/80	Mean
Tillage
Minimum tillage	17	30	24	23^a
Conventional tillage	21	22	9	17^b
Slurry application (80 kg N ha^-1)
None	-	-	-	-
Autumn	11	22	13	15^b
Spring	27	34	23	28^a
Autumn + Spring	18	24	14	18^b
Fungicides in autumn, early spring and at flowering
No	17	19	15	17^b
Yes	20	34	18	24^a
Mean	19^b	26^a	16^b

It is surprising that the values of NUE for slurry, in the absence of applied mineral N, showed only intermediate levels, whereas the highest NUE occurred in the 40/40/40 kg N ha^-1 treatment. Since the mineralization of soil N started at the end of April/beginning of May, the mineral N application at beginning of growth supported the development of the plants and enabled them to utilize N applied as a second splitting and/or as released soil N.

N-leaching

Beginning with the leaching period 1991/92, N loss was calculated by multiplying the drainage volume with the respective nitrate concentration at 90 cm depth (see also Sieling et al. 1997). The drainage volume was estimated from daily meteorological observations and evapotranspiration equations. It was assumed that after the soil water content has reached field capacity in autumn, daily drainage equalled rainfall less the evapotranspiration.

Within the crop rotation, N leaching after winter barley under oilseed rape were smallest (Table 5). A well established oilseed rape crop reduces both the leachable mineral N pool in the soil by its large N uptake and the drainage volume by its water use with a subsequent later return to field capacity (Aufhammer et al. 1994). However, after oilseed rape under winter wheat the highest N losses occurred. Due to its early development under the conditions of Hohenschulen, oilseed rape can utilize only a proportion of the nitrogen mineralized in the spring. Additional large amounts of easily mineralizable crop residue return to the soil after flowering and at harvest, whereas the N harvest index is low (0.3-0.5) compared with cereals (Aufhammer et al. 1994). Moreover, oilseed rape leaves the soil in a favourable structure. All these facts result in a considerable increase in the leaching potential after oilseed rape. Even sown early in the third week of September, N uptake of wheat before winter does normally not exceed 20 kg N ha^-1.

Table 5:   Effect of the preceding crop-crop combination on the annual N leaching
(kg N ha^-1 a^‑1) (1991/92-1996/97)

Preceding crop-crop combination	Annual N leaching (kg N ha^-1 a^-1)
After oilseed rape , under winter wheat	58^a
After winter wheat, under winter barley	48^b
After winter barley, under oilseed rape	35^c

N leaching was mainly affected by autumn slurry, but also to a smaller extent by spring slurry applied to the previous crop (Table 6). The application of mineral fertilizer N alone only slightly affected N leaching. However, the combination of mineral N and slurry increased N leaching considerably.

Table 6:   Effect of tillage, fungicides, slurry and mineral N fertilization on the annual N leaching (kg N ha^-1 a^-1) after oilseed rape under winter wheat at Hohenschulen Experimental Station (Kiel, Germany) (1991/92-1996/97)

	Mineral N fertilization (kg N ha^-1)
	0/0/0	40/40/40	80/80/80	Mean
Tillage
Minimum tillage	45	54	63	54^b
Conventional tillage	44	66	75	62^a
Slurry application (80 kg N ha^-1)
None	32	38	36	36^c
Autumn	44	62	80	62^b
Autumn + Spring	57	78	90	75^a
Fungicides in autumn, early spring and at flowering
No	43	62	68	58^a
Yes	47	57	70	58^a
Mean	45^c	60^b	69^a

Conclusion

Despite its ability to take up substantial quantities of N before winter, oilseed rape hardly utilized autumn slurry N. To minimize environmental impacts in the first or, more importantly, in the second leaching period after autumn application, slurry should be applied to oilseed rape in spring when plants are best able to use N for yield formation. In addition, the amount of N applied with slurry must be taken into account when calculating the amount of mineral fertilizer N. However, since NUE changes with the amount of applied N, it is difficult to find the best combination of slurry and mineral N fertilization.

Acknowledgement

The Collaborative Research Centre 192 was funded by the Deutsche Forschungsgemeinschaft.

References

Aufhammer, W., Kübler, E. & Bury, M. (1994). Stickstoffaufnahme und Stickstoffrückstände von Hauptfrucht- und Ausfallrapsbeständen. Journal of Agronomy and Crop Science 172, 255-264.

Barraclough, P.B. (1989). Root growth, macro-nutrient uptake dynamics and soil fertility requirements of a high-yielding winter oilseed rape crop. Plant and Soil 119, 59-70.

Chalmers, A.G. & Darby, R.J. (1992). Nitrogen application to oilseed rape and implications for potential leaching loss. Aspects of Applied Biology 30, 425-430.

Recous, S., Machet, J.M. & Mary, B. (1992). The partitioning of fertilizer-N between soil and crop: Comparison of ammonium and nitrate applications. Plant and Soil 144, 101‑111.

Sieling, K., Günther-Borstel, O. and Hanus, H. (1997). Effects of slurry application and mineral nitrogen fertilization on N leaching in different crop combinations. Journal of Agricultural Science, Cambridge 128, 79-86.