RAPESEED (Brassica napus L. var. oleifera D.C.) ECOPHYSIOLOGICAL AND AGRONOMICAL ASPECTS AS AFFECTED BY SOIL WATER AVAILABILITY

Ignazio Poma, Giacomo Venezia, Luciano Gristina

Istituto di Agronomia generale e Coltivazioni erbacee, viale delle Scienze, 90128 Palermo, ITALY

Email: POMAIGN@UNIPA.IT

ABSTRACT

A two year trial (93-95) was carried out in a representative area of Sicily, Italy (37°37' N - 13°42' E) to evaluate rapeseed bioagronomic behavior under different soil water content levels.

Using a split-plod design with three replications, three soil moisture levels (field capacity - FC, no water - STR and normal moisture - NM due to the rainfall) in interaction with two rapeseed genotypes (Brassica napus L. var. oleifera D.C.) (Active - winter variety and Ceres - spring variety) were investigated.

Weekly irrigation were necessary to maintain field capacity condition (FC), and metallic channel  among all rows of the plot were necessary to avoid rain water and to determine a plant stress condition (STR).

In both years yield decreased from optimum soil moisture conditions (FC) to the stressed one (STR) ; in fact yield performances were 126.9, 105.3, 67.9 g m^-2 in the first year and 186.8, 152.7 and 94.4 g m^-2 in the second year for FC, NM and STR thesis respectively.

The highest yield observed during the second year of trial was due to a better emergence and consequently to an higher plant density.

Analyzed parameters showed that in water limited conditions, rapeseed limits its reproductive organs differentiation like number of seeds/silique, number of siliques/plant and also shows a strong 1000 seeds weigh reduction.

In both years Active, the winter variety, performed better than the spring one (Ceres).

KEYWORD: rapeseed, ecophysiology, soil moisture

INTRODUCTION

The new trends of the European Union, aiming to food surplus reduction and to vegetal and environmental resources protection, are determining a new interest for industrial crops.

For that reasons and because the need, in the semi-arid Mediterranean environments, of an economically suitable crop for the Sicilian cropping systems rapeseed could found a right place in the inland environment of Sicily (Benvenuti and Salera, 1999).

In Italy rapeseed (Brassica napus L. var. oleifera D.C.) do not perform well, but the economic support of the Economic Community, allowing to an increment of land cultivated, reaching during 1997/98 about 101.00 hectares.

The specie  widely cultivated in the South part of Italy, is characterized by low productive stability because the erratic climatic trend, the unsuitability of cultural techniques and because a lack in varieties choice (Marzi, 1998), even though 96 varieties are registered in the Italian National Varieties Register.

To refining agronomic techniques to improve rapeseed suitability for the semi-arid environment, seems to be very important the soil moisture control during stem elongation and flowering. During those phases rapeseed prefers low temperatures, while during grain filling it tolerates high temperature but not tolerate soil water shortage, determining, if not, oil content and yield decrease (Toniolo, 1989).

While in other countries rapeseed water requirement, also in relation to cultural practices, is deeply studied (Choudhury et al., 1990; Francois, 1994; Gill and Narang, 1992), in Italy there is a lack on the argument.

For the importance of soil water content in yield stabilization, the aim of this paper is a contribution to the knowledge of the water soil content availability (from stem elongation to silique maturity) on grain yield and on main yield components.

MATHERIAL AND METHODS

The trial was carried out at the University of Palermo experimental farm "Sparacia" (37° 37^' N – 13° 42' E) on a clay representative soil of the pedological conditions of Sicily- Italy.

During the two-year trial, using a split plot design with three replications, two rapeseed (Brassica napus L. var. oleifera D.C.) varieties (main plot) (Ceres winter habitus and Activ spring habitus) in interaction with three soil moisture levels (sub-plot) were compared (field capacity - FC, no water - STR and normal moisture - NM due to the rainfall).

Weekly irrigation were necessary to maintain field capacity condition (FC), and metallic channel  among all rows of the plot were necessary to avoid rain water and to determine a plant stress condition (STR).

For the FC thesis carried out weekly, water quantity varied in relation to maximum crop evapotraspiration.

Maximum crop evapotraspiration was calculated using a class "A" PAN and adjusted by the environment coefficient and crop coefficient (FAO n° 24).

Irrigation period varied in relationship of the ripening stage of the two compared varieties.

In both year irrigation started for both varieties the first decade of the month and ended with the silique ripening.

The main agronomic techniques and informations in tab. 1 are reported.

RESULTS

Climatic trend during the two-year trial, even though reflecting the average climatic trend of the area, presented some particular aspects. During the first year, in fact, an high soil moisture content was determined by continuous and plentiful rain fall since October, limiting seeding possibilities in the opportune period. Nevertheless both rain after rapeseed seeding and temperatures, in both year, allow to a regular development of crop germination and emergence.

From figure 1, the two- year of trial did non differ as far as temperature is concerning, but on the contrary many differences in the rain trend were found.

In fact the first year was characterized by substantial and well distributed during the cultural cycle rainfalls except in March where no rainfall were recorded; on the contrary in the second year showed more regularity but quantities were not sufficient to balance evapotraspirative demand of the trial environment.

Rainfall during cropping period was 377 mm in the first and 225 mm during the second year with a 40 % reduction.

A sharp examination of the climatic data show that about 2/3 of the first year rainfall  fall during the sowing-spring period and not utilizable by crop because exceeded field capacity.

For that reasons rapeseed productive differences during the two-year trial are not due to climatic trend but are due to the different emergence density; in the first year, in fact, were lower because a faulty seed bed preparation for the extreme soil moisture (52 plants m^-2 n the first year and 65 plants m^-2 in the second).

From figure 2, reporting mean year per hectare, c.v. Active reached the best results (2 t ha^-1 in the second year), while c.v. Ceres recorded lower values.

Water effects on rapeseed yield are stressed by recorded yield levels in relationship to the three studied thesis. Higher performances in the irrigated plots (FC) were obtained, while in the stressed one (STR) yield was meanly 52% lower. Yields, in fact, were 1.27 (FC), 1.05 (NM) and 0.68 (STR) t ha^-1 in the first year and 1.87 (FC), 1.53 (NM) and 0.94 (STR) t ha^-1) in the second year (fig. 3).

High significance ANOVA for the interaction between c.v. and water, showed the high performances of c.v. Active X FC interaction; that variety under optimal soil water content yielded 2.61 t ha^-1; in the first year, 0.5 t ha^-1, the lowest yield was reached by c.v. Ceres X STR interaction (fig. 4).

All yield components showed a similar trend of grain yield. Particularly , number of silique/plant was 55.8 and 55.2 for c.v. Activ and c.v. Ceres respectively; it also was negatively influenced by water stress level (20.4 % less in the STR thesis respect to FC).

Also number of silique per plant and number of seeds per plant were correlated to genotype and water stress, showing the higher values for Activ X FC and the lowest for Ceres X STR interaction (AA.VV., 1993; Leto et al., 1998).

1000 seeds weight ranged from 1.71 to 2.90 g in the first year and from 1.5 to 2.81 g in the second year for Ceres X STR and Activ X FC interaction respectively.

CONCLUSIONS

Results of the two-year trial agree with observations of others Authors in other South environment of Italy characterized by similar pedoclimatic conditions.

In those environments, the scarce spring rainfall, is an important rapeseed yield limiting factor with a strong genotype interaction.

Several studies stressed the importance of water needs during flowering-ripening period, particularly for the winter habitus varieties, to limiting plant yield reduction.

Flowering earliness of those varieties, in fact, allow to an armony among ripening and fruit set and low evapotraspiration rate and a sufficient soil water content.

Spring varieties earliness could permit to the crop, moreover, to utilize late spring rainfall. Environment condition effects mainly influenced the number of seeds/silique, showing the fundamental role of that yield component for the determination of rapeseed production.

Water stress (STR thesis) determining a cutting of the number of seeds/silique (meanly of 20%) and a lower 1000 seeds weight can justify yield differences respect to FC thesis.

The no significance observed for those characters between FC thesis (234 mm of water during the cropping season) and NM thesis (102 mm from flowering to ripening in the first year) stress water  role in the determination rapeseed yield.

In conclusion, reported data confirm the possibility of the rapeseed grown in the semi-arid Mediterranean environment only using early growing varieties able to reach grain fill stage before the dry period start.

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