Annual self-reseeding legumes effect on subsequent crops into a rotation program in Mediterranean organic farming systems

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16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
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Annual self-reseeding legumes effect on subsequent crops into a rotation program in Mediterranean organic farming systems

Al-Bitar, L.1, Wehbé, E., Ayoub, M. & Jamea, M.

Key words: annual self-reseeding legumes, Trifolium spp., Medicago spp., biological nitrogen fixation, Mediterranean region.


Biological Nitrogen fixation (BNF) should be the most important means for N supply in organic agriculture. This study aimed at assessing the effect of fifteen legume cultivars on subsequent crops in three consecutive growing seasons to identify the most efficient and suitable ones as building crops in rotation programs under Mediterranean environment. T. subterraneum cv. York and T. glanduliferum cv. Prima, induced the best effects on wheat, particularly on total biomass, number of grains, dry matter production and increased yield by 670% and 567% respectively more than the control.


The adoption of BNF, an important process that comes second after photosynthesis (Brady, 1990) might be a solution for poor farmers in less developed countries (Hungria and Vargas, 2000; Dobereiner, 1994). Large amounts of atmospheric nitrogen are fixed in the soil-building crops (legumes), a fundamental pillar of a crop rotation program (Gresshoff, 1990) and a constitutional element of sustainability (Caporali, 2004). Legumes can improve soil quality through their beneficial effects on soil biological, chemical and physical conditions (Biederbeck et al., 1996). This study aims at assessing the fertilization effect of legumes on subsequent crops comparing the results over three years and evaluating the performance of subsequent crops.

Materials and methods

This paper presents a three-year investigation program carried out in the framework of a PhD study (Al Bitar, 2005) aiming at introducing as soil-building crops 15 Mediterranean native legume cultivars grown from November 2002 to March 2004 then green manured. Subsequent crops succeeded over three seasons: Lettuce (April - June 2004) - Corn (June - October 2004) and Wheat (December 2004 – June 2005).

Legume cultivars were the following: Biserrula pelecinus cvs. Casbah and Mauro, Medicago sphaerocarpa cv. Orion, Ornithopus compressus L. cvs. Avila and Santorini, O. sativus cv. Cadiz, Trifolium glanduliferum Boiss. cv. Prima, T. hirtum All. cv. Hykon, T. incarnatum L. cv. Caprera, T. michelianum Savi. cvs. Bolta and Paradana, T. subterraneum cvs. Dalkeith and York, T. vesiculosum Savi. cv. Cefalu and T. spumosum cv. WCT36.

The trial was carried out at the Mediterranean Agronomic Institute of Bari (IAMB) located in Apulia, south of Italy, characterized by a Mediterranean climate with humid mild winter (precipitations 400 to 500 mm) and hot dry summer. Soil is characterised by: organic mater (1.56%), pH (8.48), N (502 ppm), P (95 ppm), K (650 mel l-1).

Legume cultivars and control, a green fallow, were arranged in a randomised complete block design with three replicates, each plot of 10 m2; upon flowering in their second growing cycle they were green manured and three subsequent crops (lettuce, corn and wheat) succeeded.

Biomass production (fresh and dry) was determined on green manures by sampling plant parts including roots on an area of 0.25 m2 per plot. Samples were oven-dried at 70 °C for 48 h, crushed and digested by H2SO4 and HClO4 acid mixture. Total N was determined in the digested extracts by the standard semi micro-Kjeldahl procedure and Carbon content by Walkley and Black method (Jakson, 1967). Crop analyses were also made periodically to evaluate the subsequent crops performances by measuring several quantitative and qualitative parameters.

Analysis of variance was done by the Statistical Analysis System (SAS, V8). The effects were tested using the General Linear Model, multiple comparison of means according to Duncan’s multiple range test (Homogenous Groups, α = 0.05). Combined data for the three subsequent crops were calculated in order to compare the cumulative effects of the cultivars on the subsequent crops by analysing the variance.

Results and discussion

Most of tested cultivars seemed to perform well. However, WCT36 was the most performing since it produced the highest amount of biomass (17.6 t ha-1) with highest N content (600 Kg ha-1). Cultivars of the genus Ornithopus were the less performing and T. michelianum died before fruit setting overgrown by weeds (Orobanche spp.)

Relative results on the 3 subsequent crops (table 1) were calculated by the following formula: Relative result = (Cultivar– Control) values/ Control value*100 = Relative value in %. Thus, it refers to the increasing effect of the cultivar in comparison with the control on the concerned parameter of each of the three subsequent crops.

Tab. 1- Cumulative effect of legumes cultivars on the yield and plant nitrogen uptake of the three subsequent crops.

Legume cultivar

Plant nitrogen uptake

Marketable yield (fresh matter)

Relative value (%)

Relative value (%)

B. pelecinus Casbah

182,57 bc

275,48 abc

B. pelecinus Mauro

197,36 abc

276,43 abc

M. sphaerocarpa Orion

222,62 ab

254,63 bc

O. compressus Avila

170,77 c

237,31 bc

O. compressus Santorini

173,88 bc

250,27 bc

O. sativus Cadiz

165,9 c

220,43 bc

T. glanduliferum Prima

186,99 abc

324,85 ab

T. hirtum Hykon

202,1 abc

259,13 bc

T. incarnatum Caprera

173,59 bc

240,69 bc

T. michelianum Paradana

156,8 c

202,07 cd

T. michelianum Bolta

176,43 bc

254,56 bc

T. spumosum WCT36

194,11 abc

296,62 abc

T. subterraneum York

232,66 a

378,21 a

T. subterraneum Dalkeith

168,69 c

279,72 abc

T. vesiculosum Cefalu

173,86 bc

241,72 bc


100 d


15.21 t ha-1

100 cd


6.61 t ha-1


0.23 t ha-1

The values that do not have the same letter are significantly different at α = 0.05 (Duncan test).

All cultivars (except Paradana) showed to induce a significant increasing effect on yield at long term. The overall yield for the three crops was higher than the control ranging from 120% (Cadiz) up to 278% (York). Significant difference was found also among cultivars. York, Prima, WCT36, Dalkeith, Casbah and Mauro were the best performing over the three-year experiment. Moreover, cultivars induced also a significant increasing effect on both plant height and nitrogen uptake of the three crops ranging from 13% to 26% and 66% to 132%, respectively.

Residual effect of legume cultivars on the three subsequent crops are shown in fig 1. The effect of legumes on plant height decreased significantly from one season to another following a normal trend. Nitrogen uptake was higher than the control in the three seasons by at least 58% as found by Ten Holte & Van Keulen (1989) and Schroder et al. (1997). The highest value, significantly different from the first and the third seasons, was reached during the second growing season. The increase in terms of nitrogen uptake by the second subsequent crop could be explained by the late release of nitrogen from the nitrogen-fixing bacteria, whereas, the decrease observed in the third growing season may be normally due to the decrease in soil nitrogen content after its use by the first and the second subsequent crops.

Figure 1 - Beneficial residual effects during the three seasons. Values that do not have the same letter are significantly different at α = 0.05 (Duncan test).

The increase in crop yield following legumes was expected and it comfirmed previous results (Ten Holte & van Keulen, 1989; Schroder et al.,1997 and Breland,1996). The positive effect of legumes decreased from the first to the second season, and then it increased drastically in the third. This may be explained by the fact that soil fertility in control plots decreased much faster than in the treated plots reaching very low levels in the third season; in other words, legumes have sustained soil fertility.

Different trends of plant nitrogen uptake and plant height might be due to plant behaviour and its physiology concerning the response to nitrogen; for instance, the difference in terms of soil fertility between treated and control plots, mainly soil nitrogen content, had clearer effect on wheat (third crop) yield than on plant height, due to the high nitrogen requirements for wheat grain formation in respect to its requirement for plant growth and development.


Most of tested cultivars showed to have a large potential to be used in sustainable Mediterranean agro-ecosystems in that they possess a large screen of characteristics making very wide their possible use (Talamucci, 1997).

Cultivars York and Prima were the best performing during the whole investigation program. WCT36 was the most performing in terms of biomass production and N fixation, making it highly recommended for green manuring.

The tested legumes showed also to induce a beneficial effect on the three subsequent crops in comparison to control by stimulating higher yields, higher plant height and better plant nitrogen content for the subsequent crops. The residual effect of legumes was still concrete even after three consecutive crops as was proved by Ten Holte & van Keulen, 1989; Schroder et al.,1997 and Breland, 1996. It could be concluded that the integration of annual self-reseeding legumes into Mediterranean organic cropping systems may contribute largely to sustain long-term soil fertility, to satisfy cash crops needs in N and to increase markedly production.

Although the results are very promising, they still very preliminary considering the short period of the experiment; in fact, further studies are being conducted to sustain the obtained results.


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1 Mediterranean Agronomic Institute of Bari, Via Ceglie 9, 70010 Valenzano (Ba) Italy, e-mail;

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