Banca de DEFESA: RICARDO AMARO DE SALES

Biological fixation and nitrogen transfer using a legume in dwarf plantain cultivation in an organic system

Musa spp, green manure, organic agriculture.

The use of leguminous tree species in green manure in fruit orchards can be a viable alternative to meet the demand 

for Nitrogen (N) in mineral nutrition. Information related to the biological fixation potential of N2 from the air (FBN) 

for legumes and their contribution to the supply of this macronutrient in areas cultivated with orchards is important

 to assist in choosing the most suitable species for green manure. Therefore, the general objective of this work was 

to estimate the FBN and N transfer using the method of natural abundance of 15N, from the legume gliricidia 

(Gliricidia sepium (Jacq) Pers.); and also, quantify the supply of nutrients and evaluate the development in the

 system in the organic cultivation of ‘Terra’ type bananas (plane trees). The experiment was conducted at Fazendinha

 Agroecológica Km 47, together with EMBRAPA Agrobiologia, UFRRJ and PESAGRO-RIO, located in the municipality of

 Seropédica/RJ; set up in a randomized block design (DBC), in a factorial scheme (3x3), with three banana cultivars

 from the earth group (Curare Enano, Red Yad and Tipo Velhaca) versus three levels of organic fertilizer 100, 200 

and 300 kg ha-1 of organic nitrogen based on mannon cake and Gliricidia sepium. The works were divided into

 three parts or Chapters. In Chapter I, the phytotechnical aspects of banana growth and production were

 evaluated using the following descriptors: pseudostem height, pseudostem diameter, width of the third leaf,

 length of the third leaf, estimate of leaf area, number of active leaves at flowering and at harvest, total leaf

 mass at harvest, total pseudostem mass at harvest, total rhizome mass at harvest, days from planting to

 flowering, days from flowering to harvest, days from planting to harvest of cultivars, rachis mass, mass of the 

stalk, number of bunches, total number of fruits, average mass of the bunch, number of fruits on the second

 bunch, mass of the second bunch, mass of the fruit on the second bunch, length of the fruit on the second

 bunch, diameter of the fruit on the second bunch, skin thickness, total bunch mass, fruit mass per bunch and

 productivity. As more expressive results, the descriptors pseudostem height and total leaf and rhizome mass

 at harvest showed the same response pattern, being better at doses of 200 and 300 kg ha-1 organic N contributed

 with castor bean cake and gliricidia sepium. The productive variables length of the second fruit, mass of the

 second bunch and mass of the fruit of the second bunch showed the same pattern of responses at doses of 200

 and 300 kg ha-1 organic N contributed with castor bean cake and gliricidia sepium. The cultivars “Curare Enano”

 and "Red Yad" increased the number of leaves at flowering and bark thickness with a maximum dose of 300 kg

 ha-1 of N contributed with castor bean cake and gliricidia sepium. In Chapter II, quantification of the dry matter

 stock, accumulation and export of nutrients from the cultivar ‘Curare Enano’. To this end, quantities of nutrients

 (N; P; K; Ca and Mg) accumulated in the various organs of the plant were evaluated, such as: rhizome,

 pseudostem, leaves, stem and fruits. To calculate the quantities exported, the organs were calculated: fruits 

and stems and the quantity returned to the soil included the other organs: rhizome, pseudostem and leaves. 

The production of dry phytomass, both incorporated into the soil and removed by harvest, did not show significant 

differences between the doses of organic nitrogen applied. The different parts of the banana plant presented 

different concentrations of nutrients, with potassium being the most abundant in the fruits, stem, pseudostem 

and rhizome, while nitrogen was the highest in the leaves. The accumulation of potassium in banana plant organs

 varied depending on the type of tissue, with the pseudostem being the one that showed the greatest accumulation

 of this nutrient, followed by the rhizome, fruit, leaves and stem. On average, potassium and calcium were the

 macronutrients most returned to the soil after harvest. Nitrogen and potassium were, on average, the 

macronutrients most exported by the banana harvest. In Chapter III, to quantify the estimates of FBN and the 

transfer of fixed N derived from legumes, the natural abundance techniques of 15N were used. To apply isotopic 

techniques, it is necessary to use non-nitrogen-fixing plants (control).  Thus, two strategies were applied, the first

 consisted of collecting plants that grew spontaneously among the Gliricidia sepium bank and the second strategy

 consisted of growing spontaneous plants (non-nitrogen fixers) in a greenhouse.  The average biological nitrogen

 fixation was calculated, as well as the average nitrogen transfer to banana plants. In this study, it can be observed

 that the average biological nitrogen fixation (BNF) was 42.14%, highlighting the relevance of the legumes

 investigated as sources of nitrogen in cropping systems. The application of the highest dose of this legume

 caused a transfer rate of 18% of nitrogen to banana plants.