Use of Mexican sunflower as green manure

tithonia diversifolia (Hemsl.) is commonly known as Mexican sunflower (Brazil), buttercup or mirasol (Colombia), yellow flower or arnica-da-terra (Venezuela) and yellow daisy (Cuba). It belongs to the Asteraceae family and develops as a semi-herbaceous, erect, vigorous, branching shrub. Originally from Mexico, it is currently distributed throughout the humid and sub-humid tropics in Central and South America, Asia and Africa. It is found from sea level to up to 2.400m in altitude and in places with rainfall between 800mm/year and 5.000mm/year.

This plant can reach two to five meters in height when growing freely, with bright yellow or orange inflorescences. It can be propagated through seeds or vegetative parts. The seeds of this species have low germination immediately after being harvested in the field, but there is a constant increase in the seed germination rate, reaching up to 97,5% four months after harvest. However, propagation through cuttings has still been the most used, as it is easy to take. In this case, it is recommended to use cuttings 20cm to 40cm long, taken from the middle third of the green stems.

There is evidence that plants T. diversifolia they accumulate nitrogen in their leaves much as legumes have high levels of phosphorus and potassium, a large root volume, a special ability to recover the shortage of nutrients from the soil. Furthermore, it is considered a rustic plant, presenting a wide range of adaptation to soil and climate conditions, such as acidity and low soil fertility, high temperatures and drought. Added to this, plants T. diversifolia They support pruning at ground level or even burning with a great capacity for regrowth and recovery of plant biomass.

T. diversifolia has multiple uses. In the agricultural area, it can be used as green manure, a plant with nematicidal action, allelopathic effect on weeds, attraction of beneficial insects in some crops, living fence and ornamentation; in beekeeping, as a source of nectar; in the nutritional area, as a food supplement or food base for various animals; in the medical field, as a herbal medicine against various illnesses such as hepatitis and some infections; between others.

THE USE OF TITHONIA AS GREEN FERTILIZER

One of the biggest challenges for agriculture in the 21st century will be to develop sustainable agricultural systems that can produce food in sufficient quantity and quality without affecting soil and environmental resources, as is the case with the scarcity of phosphorus reserves on the planet. Within this context, the use of green manures is essential to production in agroecological production systems, as it helps to conserve soil and water, and to provide nutrients in different cultivation systems. The species used to produce green manure vary depending on the climate, soil and socioeconomic conditions of the farmer. Perennial or semi-evergreen species are preferable to annual ones, as they provide greater autonomy to the producer due to the permanent supply of biomass, whether through pruning or the deposition of leaves, in the case of afforestation of crops with deciduous species.

The biomass of T. diversifolia It has great potential as a natural fertilizer and can be used by farmers as green manure, as it provides adequate and necessary nutrients to improve the production of many crops, thus contributing to an increase in production and a reduction in expenses with the use of inorganic fertilizers.

Its use as green manure is recommended for short-cycle improved fallow systems, as it restores soil fertility, increasing the productivity of subsequent crops. This is due to the high foliar concentration of nitrogen, phosphorus and potassium, and the fact that these nutrients are quickly released in forms available to plants during the decomposition process. In Kenya and other parts of Africa, leaf analysis of T. diversifolia revealed relatively high concentrations of N, P, K, Ca and Mg, when compared to most legume species used in biomass production. Furthermore, the species has rapid growth and low demand for inputs, with few demands on the management of its cultivation.

Nutrient concentrations in the green biomass of T. diversifolia, when compared to the green biomass of most leguminous species used as green manure, are relatively high (Table 1).

This species also has high productive potential. In Vietnam, its green mass production exceeded 170t/ha/year, equivalent to 25t/ha/year of dry mass. In some locations in Kenya, higher values ​​were obtained (55 tons of dry mass/ha/year).

There are many reports of research carried out, mainly in Africa, Colombia, Cuba, Venezuela and some Asian countries, testing T. diversifolia alone and in addition to inorganic fertilizers, in various annual crops. In all studies, its high potential as green fertilizer has been demonstrated. In vegetables, at an international level, there are also some reports of the use of T. diversifolia as green fertilizer in the production of lettuce, carrots, cauliflower and tomatoes, with highly favorable results for its use.

RESEARCH CARRIED OUT IN BRAZIL

In Brazil, the first experiments with T. diversifolia, at an agronomic level, were carried out at the University of Marília, São Paulo. In 2007, the first dissertation on biomass production and the nutritional quality of this species was published. Several experiments were carried out with tomato, eggplant, arugula and mainly lettuce, as well as corn and beans.

In lettuce and arugula crops, several studies were developed evaluating different dosages of fresh arugula pasta. T. diversifolia as green manure compared to NPK fertilizers. The best results were related to the association of T. diversifolia with chemical fertilizer. The results demonstrate that when using  T. diversifolia it is possible to considerably reduce the use of chemical fertilizers, thus reducing production costs.

Research carried out comparing the effect of T. diversifolia with some legumes and organic fertilizers in lettuce, tomato and eggplant, highlight the potential of T. diversifolia like green manure. Thus, for organic vegetable production, the use of T. diversifolia as a natural fertilizer it is a viable option given the various attributes presented by this plant.

Starting in 2015, some public institutions in Brazil, such as UFMG, UFPI, Instituto Federal do Norte de Minas Gerais and Embrapa began carrying out agronomic research with this species, and some results are already being published. For example, at the Federal University of Piauí, starting in 2015, research was carried out to verify the potential of T. diversifolia as an alternative to nematode management Pratylenchus brachyurus in okra. The researchers concluded that both the incorporation of fresh leaves of T. diversifolia, such as mulching with leaves T. diversifolia on the soil, in the form of dry phytomass, provided a significant reduction in the population of P. brachyurus in the soil and okra roots.

T. diversifolia It is a plant with low implementation costs, easy cultivation and high return potential, especially taking into account the diversity of uses to which it can be used, such as nematicide, animal feed and green manure. The work carried out to date presents compelling results regarding its ability to provide nutrients and optimize the development of crops, especially vegetable crops. Despite this, little of its potential has been explored, especially due to the limited dissemination of the properties of this plant and, consequently, farmers' lack of knowledge of the benefits they could obtain from its use.

Ronan Gualberto, Daniel De Bortoli Teixeira, Lucas Aparecido Gaion, University of Marília Unimar

Growing Vegetables and Fruits September 2019 

With each new edition, Cultivar Hortaliças e Frutas publishes a series of technical content produced by renowned researchers from all over Brazil, which address the main difficulties and challenges encountered in the field by rural producers. Through research focused on controlling the main pests and diseases in vegetable and fruit cultivation, the Magazine helps farmers in the search for management solutions that increase their profitability. In the September 2019 edition you can also see: 

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