Use of gradual release fertilizers in sugarcane

Regular and continuous supply of nutrients to plants, lower frequency of applications to soils, reduction of nutrient losses due to leaching, immobilization and volatilization, as well as elimination of damage caused to roots by high concentration of salts are among the advantages of controlled release of fertilizers in sugarcane.

Sugar cane is cultivated in almost all Brazilian agricultural regions, which covers soils with fertility variable and, consequently, different production environments. In this context fertilization becomes an indispensable factor for the full development of culture, with the aim of obtaining high productivity.

Fertilization is objective to provide the plant with all the nutrients, without which the vegetable cannot completes its cycle. The practice of fertilization, in addition to being one of the factors essential for the development of plants, if managed correctly can considerably accelerate your growth, reduce production costs and enable greater productivity (Malavolta,1980). In this context, advances must be made in nutritional programs with regard to the efficiency of use by different cultures, such as sugar cane.

An alternative fertilization to increase efficiency of use by plants concerns the use of encapsulated fertilizers, called gradual release fertilizers. These fertilizers, once applied to the soil, they release nutrients gradually due to the coating with chemical and/or organic substances.

The gradual release of nutrients depends on humidity and soil temperature, since the temperature promotes expansion of the soil layer resin, causing an increase in its permeability to water. This process occurs regardless of soil permeability, pH or microbiological activity, which can vary from a few months to almost 20 months for full release, with the specific longevity of each fertilizer formulation.

Scientific works report that the main Advantages of gradual release fertilizers are the regular supply and continuous supply of nutrients to plants, lower frequency of applications to soils, reduction of nutrient losses due to leaching, immobilization and, also, volatilization, elimination of damage caused to roots by high concentration of salts, greater practicality in handling fertilizers, contribution to the reduction of environmental pollution by NO-3, attributing ecological value to agricultural activity (less contamination of groundwater and surface water), and reduction in production costs.

The use of release fertilizers Controlled technology adds to these advances, due to the protective effect of layers of polymers that surround the granules, reducing leaching effects, volatilization and adsorption by soil colloids, making nutrients more accessible to the root system and consequently improving the efficiency of use by plants.

With the aim of To evaluate the agronomic efficiency of these fertilizers, a field conducted by the Sugarcane Center – IAC, in sugarcane ratoons from third cut, in the municipality of Serrana, São Paulo, in a Red Oxisol mesohalic, sandy loam texture.

The sugarcane variety used in the experiment was RB 86-7515, presenting the characteristics of high agricultural productivity and rusticity, high sucrose content, medium tillering, mid to medium harvest end of harvest and tolerance to main diseases.

The treatments were constituted by the application of controlled release fertilizers in proportion of 50%, 75% and 100% in relation to conventional fertilizer. It was used two sources of controlled release fertilizer, one with 60% of the formulated with controlled release and 40% conventional, another 40% of the formulated with controlled release and 60% conventional. Conventional fertilization was carried out as recommended by the Bulletin 100 IAC, according to the results of soil analysis, in the amount of 120 kg/ha of N and K2O and 30 kg/ha of P2O5, as well as a control treatment, without application of fertilizers, as described in table 1:

Fertilizers of controlled release used in the test had longevity of release for Nitrogen around 120-150 days, while for potassium around 120-180 days.

An important piece of information in this study says respect to rainfall data. According to figure 1, total precipitation occurred during the conduct of the test, between the months of December/13 in September/14 it was just 762,2mm of rain.

The results of the study showed some interesting answers. The data obtained for agricultural yield, expressed in tons of stems per hectare, can be analyzed in table 2.

It is observed from the data described in table 2 a distinct group of three averages in relation to income of stalks per hectare. The lowest average is assigned to the absolute witness, or that is, without fertilization, this being an expected parameter. Another group intermediate, consisting of a dosage of 50% of conventional fertilizer with controlled release fertilizers in the proportion of either 40/60 or 60/40 (controlled/conventional) on straw and 75% of conventional fertilization 60/40 (controlled/conventional), incorporated under the straw. Another group with higher average in agricultural yield, superior to conventional fertilization, compost by 75% and 100% of both 40/60 and 60/40 (controlled/conventional) applied to sugarcane straw.

However, it is observed low productivity in sugarcane fields, regardless of different treatments studied in the test, which can be explained mainly by the amount of rainfall during the test conduction period, remaining well below the water requirement required by sugarcane cultivation, which requires annual rainfall of approximately 1200-1500 mm well distributed throughout the period for good vegetative development, which directly reflects on the productivity.

It is observed from the data from figure 1 that precipitation during the test was only 762,2 mm, insufficient for the water demand of sugarcane and still with distribution uneven. It is possible to verify in December 2013 a condition rainfall above the historical average, however, between the months of January to March 2014 the rainfall distribution was well below average. In this period there is a great demand for water by the plant, due to the rapid growth. The low rainfall during this period may have contributed to the lower productivity of the sugarcane field.

Regarding the technological characteristics of sugar cane, it is possible to verify from the data presented in tables 3 and 4 that the different doses of gradual release fertilizers in relation to conventional fertilization provided similar average values ​​for Brix, Fiber, Pol, Purity, Sugar contents Reducers and ATR.

Were evaluated also the foliar nitrogen and potassium contents related to the doses of gradual release fertilizers compared to conventional fertilization, described in table 5.

 How the effects of different treatments can be observed did not influence leaf nitrogen and potassium contents

Leaf nitrogen levels, considered adequate for sugar cane, for leaf samples +1 in the full phase vegetative development, are in the range of 18 g/ kg – 25 g/ kg, and the potassium between 10 g/kg – 16 g. kg, with the average values ​​being provided by the different treatments within the acceptable range for that crop.

According to results achieved in this study related to the production environment in which the test was conducted, it can be concluded that fertilization with controlled release in the proportion of 75% of conventional fertilization provided the same stalk yield per hectare compared to 100% fertilization conventional, without affecting the technological characteristics of sugarcane and the leaf nitrogen and potassium contents.

Article published in issue 225 of Cultivar Grandes Culturas, February, 2018.