Sunflower sowing consociated with Trifolium pratense L., Trifolium repens L. or Lotus corniculatus. A productive alternative

Sunflower sowing consociated with Trifolium pratense L., Trifolium repens L. or Lotus corniculatus. A productive alternative.

Sánchez Vallduví, G.E., L.N. Tamango, M.A. Eirin, J. Gomez, R. Taus, R.D. Signorio.

Course of Oleaginous Plants and Regional Crops. Course of Polygastrica. School of Agricultural Sciences and Forestry. UNLP. 60 y 119 CC Nº 31, La Plata, Buenos Aires. CP 1900. gvallduv@agro.unlp.edu.ar

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  Sunflower cultivation in Argentina is set within a continuous increase in the grain production process known as “agriculturization”. One of the undesirable consequences of this process is biodiversity reduction, which attempts on the sustainability of the agroecosystem. Mixed farming systems and consociated sowing are alternatives to improve sustainability. In our country, the sunflower is usually part of the agricultural-livestock rotation, and sunflower-forage legume intercropping systems can be considered as a strategy to enhance the quality of the mulch and contribute to the diversity. The objective of this work was to determine the crop yield and the aerial biomass production of commercial sunflower hybrid with Trifolium pratense L., Trifolium repens L. or Lotus corniculatus intercropping system.
  
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  The experiment was carried out with a randomized block design. The treatments were: sunflower in monoculture, with and without herbicide, and intercropping sunflowers with red clover, white clover or lotus, at two sowing densities (normal and high). At harvest, the sunflowers’ ripeness and total biomass, the crop yield, legumes and weed were evaluated. Results were statistically analyzed using ANOVA and LSD test (p ≤ 0,05).
  
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  The average grain yield of the sunflower in this trial was 4462 kg.ha^-1. The maximum value of this variable was achieved when herbicides were applied (5120 kg.ha^-1). Among the other treatments, the crop yield did not differ statistically: values ranged between 3940 and 4810 kg.ha^-1.  In the treatment of sunflower in monoculture without herbicide application, the total biomass (sunflower + legume + weed) achieved at harvest ripeness was 17472 kg.ha^-1, a value which did not differ significantly from any other mixture. The number of legume plants obtained varied according to the species. The establishment of white clover was the lowest, making a poor biomass contribution. This variable was significantly higher in the treatment of sunflower with red clover at high density (1320 kg.ha^-1). Moreover, among the other treatments, it is worth mentioning the values reached by the mixture of sunflower with red clover at normal density and with lotus at high density (568 and 380 kg.ha^-1 respectively).
  
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  The results obtained show that the sunflower intercropping with these forage legumes could be regarded as a productive alternative to improve the crop residues’ quality. This could yield stubbles of a higher nutritional value or a better quality of plant biomass, which is incorporated to the soil after sunflower harvest. Furthermore, these systems could improve diversity by guaranteeing sunflower crop production.
  
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  This study provides a breakthrough in the search for strategies which improve sustainability of extensive production systems through the reduced use of inputs, the greater biodiversity and the improved quantity and quality of stubble. However, bearing in mind that these results are from a single year of testing, it is important to continue evaluating the performance of these intercropping systems.
  

The agriculturization and simplification processes which have been taking place, generally, in our country’s agroecosystems and, particularly, in the Pampas entailed the abandonment of the crop-livestock rotation, among other things (Savilla and Pasinato, 2006). Among the emergent problems of this situation, biodiversity reduction stands out (FAO-AGLL Portal: Soil Biodiversity, 2002; Brusaard et al., 2007; Zimmermann et al., 2010). Consequently, the resilience capacity is reduced (UNEP, 1996; Stoate et al. 2001) and its long-term productivity and sustainability are called into question (Viglizzo and Frank, 2006). In this context, the need to combine the agricultural systems’ productivity with the preservation of the environment and natural resources clearly arises (Parris, 1999).

Sunflower cultivation in our country is set within this continuous increase in agricultural production and is oriented towards maximizing its grain and oil yield per ha. Despite the strong rise of land sown with soybean, sunflowers are still an important alternative of production for extensive systems in Argentina and continue to outstandingly take part in the world market (CIARA, 2011).

In recent years, awareness about the environmental, social and cultural impact of the dominant model of production has increased, leading to reconsidering a more sustainable model. A tool to restore and increase the agroecosystems’ biodiversity is the diversification of such (Viglizzo et al., 2011). Mixed production systems are an alternative to improve this issue. Moreover, they can also enhance the economic outcome. Sunflowers are usually part of the crop-livestock rotations. However, one of the constraints is their low-quality stubbles for animal feed (INTA, 2004).

The sowing consociated with forage legumes might be considered as a strategy to improve the stubbles’ quantity and quality. Furthermore, this intercropping is expected to bring other advantages to the agroecosystem (Sarandón, 2002), such as encouraging biodiversity (Malézieux et al, 2008). Additionally, the incorporation of crop residues to the soil can restore a greater amount of organic waste to the earth, thus, improving the organic matter content and its physical-biological properties (Lefroy and Craswell, 1997). Thereby, the consociated sowing is expected to be an alternative contributing to the conservation of productive resources and to the minimization of the external environmental impact, which is an essential requirement for achieving sustainability (Flores and Sarandón, 2003).

The selection of the companion species depends on the production area and it is an important factor which determines the consociation’s behaviour. Certain sowing experiments mixing sunflowers with other crops have been cited (Putman and Allan, 1992). In our country, it was noted that the sowing mixing sunflowers with red or white clovers sown in two different systems (sunflowers’ line-seeding or broadcast seeding) did not modify the crop’s productivity, preserved the stubbles’ availability and enhanced their protein content (Eirin et al, 2009). However, there is not much information available about the sunflowers’ behaviour during the consociation and about the diverse determining factors, such as the companion species and the chosen sowing system.

The goal of this work was to evaluate the yield and production of the biomass in a consociation of a commercial sunflower hybrid with Trifolium pratense L., Trifolium repens L. or Lotus corniculatus.

MATERIALS AND METHODS

A field test was carried out in the Experimental Station “Julio Hirshorn”, located on Los Hornos, city of La Plata. The climate is mild with an average temperature of 15.9º C; being January the warmest month and July, the coldest. The rainfall pattern is isohygric with a homogeneous rain distribution throughout the year, whose average value is 1045.4 mm.

The sowing took place on October 12, 2010, by means of an experimental Agrometal seeder of five grooves, in a plot whose surface horizon (0-20 cm.) analysis was: pH, 5.6; MO, 4.01 %; total N, 0.197 % and P, 19.6 ppm (Bray Kurtz I).

The randomized block design of the experiment included four replications, and the treatments were the following:

1- Sunflower in a monoculture: control.

2- Sunflower intercropped with red clover sown at a normal density.

3- Sunflower intercropped with red clover sown at a high density.

4- Sunflower intercropped with white clover sown at a normal density.

5- Sunflower intercropped with white clover sown at a high density.

6- Sunflower intercropped with lotus sown at a normal density.

7- Sunflower intercropped with lotus sown at a high density.

8- Sunflower sown in a monoculture, with the use of herbicides.

Concerning the crop’s ripeness, the yield, aerial biomass, sunflower crop index, the total aerial biomass of the system (sunflower + legumes + spontaneous vegetal community) and the N in crop residues were evaluated. The plant tissues’ nitrogen content was established by the micro-Kjeldahl method (AACC, 1983). Results were analyzed with ANOVA and test LSD (P: 0,05) for a comparison of averages.

The average sunflower’s grain yield of the test was 4462 kg.ha^-1. The highest value of this variable was achieved in the monoculture with herbicide application. By analysing the remaining treatments, it can be observed that the yield of the pure sunflower did not differ statistically from the ones of the mixtures and that the values remained close to the ones recorded in the tests of the national crop assessment network (ASAGIR, 2010). In this test, the mixtures did not enhance the yield, as opposed to what Putman and Allan (1992) recorded regarding sunflowers sown with mustard. Nevertheless, these results suggest that the consociation with legumes might be regarded as an acceptable, productive alternative, since it guarantees enough productivity of the sunflower, one the requirements cited by Sarandón and Sarandón (1993) for agriculture to be considered sustainable.

Although the absolute value of the crop residue in the sunflower-red clover mixture at high density was the lowest one of all treatments, it was the one with the highest legume proportion (7 %) (Figure 1). This established a crop residue with more N content and, thus, a higher-nutritional-value stubble is expected, which coincides with what Eirin et al (2009) pointed out while observing a better protein content in sunflowers consociated with red or white clover.

References: S: sunflower in monoculture; SR1: sunflower-red clover at normal density; SR2: sunflower-red clover at high density; SW1: sunflower-white clover at normal density; SW2: sunflower-white clover at high density; SL1: sunflower-lotus at normal density; SL2: sunflower-lotus at high density; SH: sunflower in monoculture with herbicide.

The test’s results indicate that the sunflower sowing consociated with these forage legumes might be taken as a productive alternative to enhance the crop residues’ quality. On the other hand, these systems could improve diversity, guaranteeing sufficient productivity of the sunflower cultivation (Viglizzo, et al, 2011). In the systems which do not employ herbicides, the physical and biotic properties are expected to be more preserved, which is related to, among other factors, the quality of the residues incorporated to the soil after the harvests, combining the agricultural system’s productivity with the environmental preservation (Parris, 1999).

This work contributes to the progress in the search of cropping strategies which enhance the extensive production systems’ sustainability through a lower use of inputs, greater biodiversity and through the stubbles’ quantity and quality.

Taking into account that these results were achieved in only a one-year trial, it is important to continue assessing the sunflower’s behaviour in consociated sowing.

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