**2. Material and methods**

#### **2.1 Characterization study area and experimental design**

This study was conducted on a farming site located at coordinates 02° 03′ 55.5″ S and 59° 22′ 55.5″ W, on the side roads called Morena, in the municipality of Presidente Figueiredo, about 150 km from Manaus-AM through highway BR-174, in the Central Amazonia region. The experimental site's soil was classified as Oxisol, with flat to slightly undulated relief and belonging to the very clayey textural class, with the following chemical characteristics (0–20 cm layer): pH (H2O) 4.62; available P 3.67 mg kg−1; total N 1.88 g kg−1; and 0.36; 0.16; 0,07; 2.75 cmoc kg−1 of exchangeable Ca, Mg, K, and Al, respectively.

The experiment was carried out in an eight-year-old cupuassu crop, with 5 × 5 m spacing between plants and 400 plants ha−1 density. The experimental design was a randomized block design with four blocks (replications), consisting of a 2 × 3 factorial scheme, in which the factors were two levels of liming and three types of fertilization, making a total of six treatments, totaling 24 plots with 10 cupuassu

*Organic Fertilization with Residues of Cupuassu (*Theobroma grandiflorum*) and Inga… DOI: http://dx.doi.org/10.5772/intechopen.100423*

plants per plot and a total of 60 plants per block. Treatments were as follows: 1—soil control; 2—cupuassu shell 2 t ha−1; 3—cupuassu shell 2 t ha−1 + Inga prunings 3 t ha−1; 4—Limestone 2 t ha−1; 5—cupuassu shell 2 t ha−1 + limestone 2 t ha−1; 6 cupuassu shell 2 t ha−1 + Inga prunings 3 t ha−1 + limestone 2 t ha−1.

The dolomitic limestone (2 t ha−1) was applied within the area straight below the cupuassu plant canopy and superficially incorporated into the soil. Plant materials used as organic fertilizers were obtained from farmers growing sites. Cupuassu shells were removed from a pile of discarded cupuassu shells and ground in a disintegrator (chopper and grinder), whereas the plant material was obtained from adult Inga tree pruning. Pruning was done by cutting off branches bearing up to 1.0-cm-thick leaves, just prior to the fertilization. Organic fertilizers were applied within the area straight below the cupuassu tree canopies, 60 days after the limestone was applied.

Plant materials used as organic fertilizer were analyzed to determine their chemical characteristics according to Silva [11] methodology. Inga plant material held higher nutrient concentrations than those of cupuassu shell, except for K, the contents of which showed to be similar (**Table 1**).

#### **2.2 Soil sampling and analyses**

Soil and cupuassu leave samplings were carried out at the end of the 2007 harvest, so as to evaluate soil fertility and plant nutritional status. Soil samples, within the area below plant canopies, were collected at 0–10 and 10–20-cm deep, for a total of 10 simple subsamples to make up a composite sample, and 20–30-cm deep, in a total of 5 subsamples to form one composite sample. Soil samples were airdried, sieved through a 2-mm mesh, and taken to INPA's Soil and Plants Laboratory, where they were analyzed according to the methodology used by Embrapa [12]. Soil pH was measured in water at a ratio of 1:2.5. The cations of Ca, Mg, and Al were extracted using KCl 1 N, and their concentration was measured using atomic absorption spectrophotometry. For P and K, the double acid extraction system (H2SO4 0.0125 M + HCl 0.05 M) was used. P levels were determined by spectrophotometry using ammonium molybdate. The organic carbon concentrations were obtained using the self-analyzer for C, H, and N from Carlo Erba manufacturer.

Four simple soil samples were collected at 0–5, 5–10, and 10–20-cm deep, within the area straight below the canopies of the four central plants in the plot, for 0, 30, 60, and 90 days following the organic fertilizers application, so as to determine the N in the ammonium (NH4 + ) and nitrate (NO3 − ) forms. Samples were placed in plastic bags and stored in a styrofoam box containing ice. They were then transported to the laboratory and weighed for mineral-N extraction. Mineral N contents were determined after having been extracted with 0.5 M K2SO4, by using 20 g of moist soil and 40 mL of K2SO4. Nitrate and ammonium contents were determined through colorimetry following Embrapa [12] methodologies.

The sixth recently ripened sprouting leaf, downward from the tip of one of the mid-canopy branches, was established as a standard reference in the collection of


**Table 1.**

*Nutrient concentrations in plant materials used as organic fertilizer, collected on farms in the Central Amazon region (n = 3).*

cupuassu leaves. A total of five leaves were removed from each useful plant per plot, rapidly cleaned with distilled water-soaked cotton, dried in a forced ventilation oven at 65°C for three days, and then ground. Ca, Mg, K, and P concentrations were determined by nitro-perchloric digestion and the total N through sulfur digestion followed by distillation through the micro-Kjeldahl method [12].

#### **2.3 Fruit production**

The fruit production was evaluated by the number and weight of cupuaçu of 10 useful plants of each plot, from December to April (time of production cultivation), during the 2007/2008 harvest. The fruits, once detached from the plant, were counted and weighed. This operation was carried out once a week, during the entire harvest period.

#### **2.4 Statistical analysis**

Treatment effects significance was determined by the analysis of variance (ANOVA), and the comparisons between the means of the variables were performed by the Tukey test at 5% probability.
