Effects of different temporary nitrogen deficiencies in early spring on winter oilseed rape yield.

C. Colnenne ¹ R. REAU ² and JM. Meynard ³

¹ Institut Supérieur d’Agriculture de Lille, F59046 Lille cedex Colnenne@isa.fupl.asso.fr

² CETIOM, F–75116, Paris Reau@cetiom.fr

³ Institut National de la Recherche Agronomique, F78850 Thiverval-Grignon, Meynard@jouy.inra.fr

ABSTRACT

After Winter one of the agricultural practices is the nitrogen fertilization of the winter oilseed rape. Nine field experiments have been carried out in different regions in France to analyse the opportunity of nitrogen spreading at the end of Winter. The results obtained were various according to the water stress conditions, which were particularly high in Spring this year. However, some advice may be given.

Keywords : Nitrogen Nutrition Index, yield, nitrogen fertilization

Introduction

According to the Winter pedoclimatic conditions, the winter oilseed rape presents various growth phenomena during this period. In the north of France, this crop may lose its leaves in some cases with high intensity (Triboi-Blondel, 1995), or change their coloration. These evolutions result from the low temperatures or/and the nitrogen limiting nutrition conditions (Ogunlela et al., 1989). On the other hand, in the South regions, the high temperatures allow a high growth and the plants are well developed.

At the end of the Winter, one of the agricultural practices consists of fertilizing this crop as quickly as possible to avoid a lack of nitrogen. This early spreading may be explained by the « thin » aspect of the crops in the north of France, or by a high instantaneous nitrogen requirement estimation for the developed crop in the other regions. At this period, the winter oilseed rape nitrogen fertilization may interfer with other agricultural practices, for example on cereal cropping, and the objective of this study is to analyse the necessity of a quick nitrogen supply at the end of the Winter on oilseed rape. For this reason we have analysed different temporary nitrogen deficiencies at the end of Winter on yield components.

1. Materials and methods

Nine field experiments with the winter oilseed rape cultivar Goeland were carried out during the winter growing seasons 1997, in different pedoclimatic conditions in France. In Autumn, the plants were sometimes fertilized to prevent a lack of nitrogen during this period. To test the necessity of an early nitrogen supply, a same N quantity spreading has been realized at different times at the end of Winter. According to the climatic conditions, the first application was applied when the growth increases significantly and the two others, three and six weeks after.

From the end of winter to the beginning of flowering (F1), we took regular measurements of dry matter and total nitrogen concentration (Dumas Chemical analysis) on the aerial parts to characterize the nitrogen status of the crops (i.e. Nitrogen Nutrition Index : Lemaire et al., 1989), and we measured some yield components : number of seeds/m², the weight of seeds and yield.

2. Results

2.1. Characterization of the Nitrogen deficiencies at the end of Winter

We chose to present only the results from one experiment in the South West of France : Surgeres (cf. Figure 1). The evolution of the nitrogen status of the crop is correlated to the nitrogen supply date. Earlier the nitrogen supply was applied, lower the nitrogen deficiency was (i.e. N.N.I. is higher than 1). For the two first nitrogen spreadings, the nitrogen status of crops began higher than 1 the 11 and the 21 February respectively, and stayed in non N limiting growth conditions until the beginning of flowering. For the third treatment (the latest nitrogen supply) a water stress occuring after the N spreading, didn’t allow the nitrogen nutrition of the plants. The nitrogen deficiencies were longer, and at the stage F1, the N.N.I. value was 0.89, which was not very high.

Figure 1 : Evolution of the nitrogen nutrition indes : Surgeres 1997

2.2. Consequences on yield components.

We measured different results according to the experiment situations (cf. Table 1). With the delay of the N supply, we observed :

- no significant effect on yield : 7 experiments

- a significant yield increase : 1 experiment

- a significant yield decrease : 1 experiment.

3. Discussions – Conclusion

The climatic growth conditions were characterized in 1997 by a very dry climate which were variable in the different regions. In consequence, the variability of the yield responses to the N supply delay may be explained by these water limiting climatic conditions which determined the N absorption by crops.

3.1. No significant effect on yield components

These experimental conditions were generally in the north of France, where the « regrowth » period occured at mid March. At this moment, the climate was very dry and any N supply couldn’t be assimilated by crops after N spreading. The rain which arrived after the third N supply didn’t allow to differentiate in time the N assimilation between the three treatments.

3.2. Significant yield decrease with the N supply delay.

This response has been obtained in the South of France. In this case, the winter growth conditions allowed a very high development of the crop and the first N supply was very early in January before any water stress. From February to mid April, the water stress conditions have limited the N absorption of the second and the third N supplies. For these treatments, the N assimilation has been pushed back at the beginning of flowering, date of the first irrigation. The significant yield difference between the first and the two other treatments can be explained by the very high delay of the N assimilation (i.e. at F1) in the two last N supply treatments.

3.3. Significant yield increase with the N supply delay.

This experiment has been conducted in the center of France. In this case, the different N spreading lead to a development delay between the three experimental treatments. In mid April, the very low temperatures (inferior to 0°C) induced a high loss of flowers in the two earlier N supply treatments which were at the beginning of flowering, but caused no damage to the flowers of the third N supply treatment which were less developed. In consequence, in spite of a real different N assimilation in Spring between the treatments, the cold temprature conditions at the F1 stage provoked a significant decrease in the production of the two first N supply treatments.

In conclusion, according to the particular climatic conditions of this year, it is difficult to appreciate the necessity of an early N supply immediately after the Winter period. Nevertheless, these experiments have showed that an early N fertilization has to be in coherence with :

- the increasing of the temperatures at the end of Winter, which modifies the crop growth speed and defines the instantaneous N requirements of crops,

- the soil N availability which may allow a N supply delay,

- the yield compensation potentialities of this crop, between the end of the Winter and the beginning of flowering, after a little N deficiency period at the regrowth stage.

Table 1 : Three different yield responses at the nitrogen fertilization delay at the end of Winter.

Experimental conditions	France			South of France			Center of France
	Seed weight	Seed/m²	Yield (q/ha)	Seed weight	Seed/m²	Yield (q/ha)	Seed weight	Seed/m²	Yield (q/ha)
T1	4.3	11047	47.5	3.5	10857	38.0	4.3	7791	33.5
T2	4.3	11302	48.6	3.4	10912	37.1	4.2	8714	36.6
T3	4.3	11186	48.1	3.3	10091	33.3	4.3	8674	37.3
Statistic test (P < 0.05)	n.s.d.	n.s.d.	n.s.d.	n.s.d.	d.s.	d.s.	n.s.d.	d.s.	d.s.

Seed weight in g 

T1 correspond to the first N supply , T2 and T3 respectively the second and the third one

nsd. and sd. : non significant different, and significant difference

Acknowledgements

We thank the members of CETIOM for theirs participations in data collecting, advice, and the CETIOM which finances the experiments.

References

Lemaire G., Gastal F., Salette J., 1989. Analysis of the effect of N nutrition on dry matter yield of a sward by reference to potential yield and optimum N content. Proceedings XVI International Grassland Congress, Nice, France (179-180)

Ogunlela V.B., Kullmann A., Geisler G., 1989. Leaf growth and chlorophyll content of oilseed rape as influenced by nitrogen supply. Journal Agronomy and Crop Science, 163 (73-89).

Triboi-Blondel A.M., Lardon A., 1995. Temperature effects at flowering on photosynthesis and yield of winter oilseed rape. 9^th International Rapeseed Congress, Cambridge (UK), T2 (515-517)