The rice (Oryza sativa L.) is the second most cultivated cereal and the main food for more than half of the world's population, occupying an area of approximately 163 million hectares, and can be planted under different systems and in different ecosystems, with emphasis on floodplains and highlands (FREITAS et al., 2021). Production can be affected to different degrees by rainfall, air temperature, solar radiation, and photoperiod. The average apparent consumption worldwide is 54 kg/person/year. Rice is part of the global dry grain market and is growing at a robust rate, due to increased awareness of its health benefits (United States Department of Agriculture (USDA, 2020; EMBRAPA, 2008).

          Brazil is among the largest rice producers (USDA, 2018). Rice farming is practiced using two cultivar techniques: irrigated and dryland, with the South region, mainly the states of Rio Grande do Sul and Santa Catarina, responsible for approximately 75% of national production, through the irrigated system. The rest of the production is concentrated in the states of Mato Grosso, Maranhão and Roraima, with dryland rice cultivation (CONAB, 2018).

Irrigated System

          The irrigated system requires knowledge from the rice farmer (rice producer), management, soil preparation, fertilization, seeds, among others. Presenting a high investment cost in land preparation and inputs (ROLÃO et al., 2018). The cultivation systems used in irrigated rice cultivation are distinguished, in soil preparation, sowing methods and initial water management and are titled: Conventional system, Minimum cultivation, Direct planting, Pre-germinated and Seedling transplantation (AGEITEC, 2014; CONAB, 2015; NUNES, 2016).

          The conventional soil preparation system comprises primary (plow) and secondary (harrows or planes) preparation (ROLÃO et al., 2018). Primary preparation consists of deeper operations carried out with a plow aiming to break up compacted layers and eliminate plant cover; in secondary preparation, superficial operations are carried out to level, destroy soil crusts, add fertilizers and pesticides and eliminate weeds. Sowing can be done by broadcasting or in rows (NUNES, 2016). 

          In minimum cultivation, soil preparation involves the formation of a plant cover, walling, with wide-based, low-profile rammed earth. Rice can be sown on the rammed earth, as there is adequate machinery that allows this procedure (CONAB, 2015). The seeds are thrown directly onto the plant cover dried with herbicide, without soil mobilization (NUNES, 2016).

          Direct planting employs minimal soil movement, permanent soil cover and crop rotation (CONAB, 2015). It involves operations of systematizing the soil surface or flattening, liming, construction of irrigation infrastructure and road drainage. The seed is placed directly into the soil, not exceeding 25 to 30% of the surface of the disturbed soil (NUNES, 2016).

          The pre-germinated system is distinguished by the use of pre-germinated seeds in flooded soil (ROLÃO et al., 2018). Soil preparation comprises the following operations: one or two plowings in dry soil, one or two harrowings to dilute soil clods, flattening and filling, flooding the land with a 10 cm sheet (approximately 15 days before sowing), leveling and smoothing the land using wooden planks (AGEITEC, 2014; NUNES, 2016).

          Transplanting seedlings involves the seedling production and transplanting phases. The seedlings begin to emerge, the boxes are irrigated daily until the two-leaf stage (12 to 18 days), and specific fungicides are applied. Transplanting is generally carried out around 12 to 18 days after sowing, that is, when the seedlings reach 10 to 12 cm in height (AGEITEC, 2014). Soil preparation, water management, weed, pest and disease control are similar to those of the pre-germinated system (NUNES, 2016).

          Irrigation of rice crops is conditioned by the chosen cultivation system. Therefore, the admission of one or more systems will differentiate the start and end time of irrigation, water management and use, and soil preparation (NUNES, 2016). There is a predominance of the cultivation system with leveled rammed earth, where irrigation is carried out by systematizing the crop (CONAB, 2015). This crop requires water throughout its cycle, which lasts between 100 and 140 days for cultivars in a flooded system. However, there are three phases that demand greater demand: crop establishment and tillering, beginning of panicle differentiation (IDP), and grain filling (ROLÃO et al., 2018).

          It is advisable not to remove water from the crop before 30 days after applying pesticides, only to perform blade maintenance (NUNES 2016). The harvesting operation is carried out by self-propelled harvesters that perform the cutting, collection, threshing and cleaning procedures (AGEITEC, 2014).

dryland system

          The dryland system requires few inputs and has a low initial investment cost. It differs from irrigated rice in that it is mostly carried out on dry land (COLOMBO; JÚNIOR, 2015; ROLÃO et al., 2018).

          Upland rice is grown in five situations: opening up areas, rotation with other direct-tillage grains, pasture renewal, crop-livestock-forest integration systems, and in the off-season (AGEITEC, 2014; NUNES, 2016). The rotation system promotes soil sustainability by adopting appropriate soil preparation management. Specifically, upland rice in cerrado soils has productivity that stabilizes or decreases in the second year of monoculture and decreases in subsequent years. However, when rotated every two years with soybeans, productivity increases significantly (NUNES 2016; ROLÃO et al., 2018).

          The Direct Planting System (NTS) facilitates the management of production systems. The effect of nitrogen applied to the NTS of rice cultivated after soybeans is relatively low compared to other production systems (ROLÃO et al., 2018). Rice production systems in pasture areas consist of sowing grass when the harvest is finished, as an alternative for soil preparation. Late sowing of grass reduces competitiveness between intercropped crops and allows for greater productivity of rice cultivars (NUNES 2016). Most upland rice crops are located in the cerrado region and, consequently, the soils have low fertility, evidencing fertility management as one of the essential factors in cultivation (NUNES 2016). The essential elements, nitrogen, phosphorus and potassium, are those that the plant needs in greater proportions (ROLÃO et al., 2018). The appropriate use of fertilization is a viable way to increase productivity, in addition to reducing production costs and enabling greater profitability for producers (AGEITEC, 2014; NUNES, 2016). Upland rice cultivars have a cycle between 110 and 155 days (CONAB, 2015; NUNES, 2016).

          The harvesting methodology can be carried out: manual, semi-mechanized and mechanized. The manual consists of the operations of cutting, windrowing, collection and threshing that are carried out manually; semi-mechanized, the cutting, windrowing and collection stages are manual, only threshing is mechanized; mechanized, all phases are carried out by machines (AGEITEC, 2014; NUNES, 2016; ROLÃO et al., 2018).

FERTILIZATION MANAGEMENT 

          Fertilization will be done differently depending on the cultivation system. We will first address fertilization in an irrigated system. We will follow the recommendation of the liming and fertilization manual for the states of Rio Grande do Sul and Santa Catarina, 2016.

Irrigated System

          Fertilization is associated with the expected response of the crop. Thus, high response to fertilization is expected when rice is grown under favorable climate conditions, especially high solar radiation during the production period, use of cultivars with high production potential, sowing at a time and density appropriate for the cultivation region, adequate management of irrigation, weeds, especially red rice, diseases and pests. In situations where any of these factors are not adequate, the expected response to fertilization will be average or even low, and the recommendations should be adjusted, reducing the doses of fertilizers.

          Nitrogen (N) promotes plant growth by increasing the number of tillers, panicles, and grains per panicle. Phosphorus (P) is necessary for tillering, grain formation (filling), and grain quality (BARBOSA FILHO, 1989; CASTRO et al., 2013). Potassium (K) is one of the essential nutrients for rice growth, acting in plant photosynthesis, contributing to the opening and closing of leaf stomata, and being responsible for the transport of soluble carbohydrates within the plant (SANTOS, 2018). However, in addition to all these effects, K has the ability to strengthen the cell walls of the stalk with lignin, providing greater resistance to lodging, diseases, and pests in rice (BARBOSA FILHO, 1989).

Nitrogen

          Nitrogen is the second most extracted nutrient and the most exported by rice crops (FORNASIERI FILHO; FORNASIERI, 2006). It is a constituent of numerous organic compounds such as amino acids, nucleic acids and protein (EPSTEIN, 1975). Nitrogen deficiency in rice is relatively common in Brazil, which would be related to factors such as: low organic matter content in the soil; losses by leaching and volatilization; reduced use of nitrogen fertilizers; nutritional imbalance; water deficiency (EPSTEIN, 1975; RAIJ, 1991; FAGERIA; SANT'ANA; MORAIS, 1995). It is one of the main factors involved in productivity (FAGERIA; BALIGAR, 2001; FAGERIA; BARBOSA FILHO, 2001) and in improving the nutritional quality of rice grains (FERRAZ JUNIOR et al., 1997). When supplied in quantities greater than the needs for vegetative growth, close to anthesis, it makes it possible to increase the protein content (CHING; RYND, 1978), with an increase in biological value by positively interfering in the protein fraction of glutelin (CHING; RYND, 1978; FERRAZ JUNIOR et al., 1997).

Table 1 - Nitrogen requirement for rice crops.

          For rice produced by sowing in dry soil, it is recommended to apply between 10 and 20 kg N/ha at sowing and the remainder as top dressing. 50% of the total dose should be applied at the three to four leaf stage (V3/V4) and the remainder should be applied at panicle initiation (R0 stage). However, this stage cannot be seen in the field, so the panicle differentiation stage (R1 stage) should be used as a reference. The first top dressing should preferably be applied on dry soil, before the start of crop irrigation, which should occur as soon as possible (up to 3 days). Top dressing applications after soil flooding are made over a water table. In these cases, water circulation in the crop should be interrupted for at least three days.

          For pre-germinated rice, nitrogen fertilization is not recommended at sowing, due to the risk of element loss and the low crop requirement in the initial phase of cultivation. For short-cycle (up to 120 days) and medium-cycle (between 120 and 135 days) cultivars, it is recommended to apply around 50 % of the recommended N dose at the early stage (V3/V4) and the remainder at the panicle initiation stage (R0). For late-cycle cultivars (> 135 days), the top dressing can be divided into three equal applications, at V3/V4, halfway through tillering (V6/V7) and at R0.

          The supply of N via fertilization is responsible for the increase in grain yield and components of rice yield, such as the number of tillers and panicles per unit area (SINGH; PILLAI, 1996), the number of spikelets per panicle and grain weight (MARZARI, 2005). Although rice absorbs nitrogen throughout its cycle, the requirements are greater in the tillering and reproductive phases (SCIVITTARO et al., 2018). However, it is in the latter, which begins with the initiation of the panicle, that the plant presents greater efficiency in the absorption of N for grain production, since the root system is more developed and, consequently, has greater potential for nutrient absorption (MACHADO, 1993).

          In an experiment conducted by Scivittaro et al. (2012), it was shown that the absorption of N by rice, regardless of the dose, application time and division of nitrogen fertilization in topdressing, the amount of N absorbed by rice is quite high, regardless of the fertilization management practiced, with approximately 70% exported by the grains. This demonstrates the high demand for nitrogen by the crop, as well as the need to replace the exported nutrient, via fertilization and/or by adopting cultural practices that favor its accumulation. It is also worth noting that the nitrogen level in the plant, grain productivity and nitrogen absorption by rice are predominantly influenced by the dose of the nutrient applied in topdressing, increasing proportionally to it. Grain productivity and the efficiency of N use by rice are benefited by the extension of the fertilization period until the reproductive phase. 

Match

          In the dry soil sowing system, phosphate fertilizers should be applied and incorporated into the soil at the time of sowing. In the pre-germinated system, these fertilizers can be applied and incorporated with a rotary hoe or harrow when forming the mud or after leveling the area, before sowing. What can happen is that applying it before sowing the rice and intensifying the development of algae; P can be applied as a top dressing, before the beginning of tillering, between the two to three leaf stages (V2 and V3).

Table 2 – Phosphorus requirement for rice crops.

          Regarding phosphorus availability, soil flooding promotes an increase in the availability of this nutrient for plants, mainly due to the increase in the diffusion of the element in the soil solution (soil compartment from which the plant will extract the nutrient) as well as an increase in the amount of phosphorus in the soil solution, which was previously bound in dry conditions by calcium and iron, for example (FERREIRA et al., 2008). According to research carried out by Moraes & Freire (1974), with several soils in Rio Grande do Sul, phosphorus reaches maximum concentrations in the soil solution between five and six weeks after flooding. Thus, in the cultivation of pre-germinated rice, for example, the increase in phosphorus availability occurs earlier, in relation to sowing carried out in dry soil. The dynamics of this nutrient in flooded soils partially explains the limited response of irrigated rice to phosphate fertilization, even when the levels of available phosphorus in dry soils are low (FERREIRA et al., 2008).

Potassium

          When sowing in dry soil, potassium fertilizers should preferably be applied at the time of sowing. In the case of pre-germinated rice, potassium fertilizers, as well as phosphate fertilizers, can be applied and incorporated with a rotary hoe or harrow at the time of slurry formation or after leveling the area before sowing. 

          It can be fractionated to avoid potassium losses, especially in the case of applying high doses in sandy soils. In this situation, it is recommended to apply half of the dose at the time of soil preparation (pre-germinated system) or at sowing (sowing system in dry soil) and the other half, as a top dressing, at the initiation of the panicle, together with the application of nitrogen.

Table 3 – Potassium requirement for rice crops.

          Potassium (K) is an essential nutrient for rice cultivation, acting in several physiological and biochemical processes in the plant, highlighting osmotic regulation, enzymatic activation, regulation of pH and cellular ionic balance, regulation of stomatal transpiration and transport of photosynthesis products (DOBERMANN; FAIRHURST, 2000). 

          Research results show that potassium fertilization brings several benefits to rice crops, including promoting root system development, increasing plant vigor, reducing lodging, increasing resistance to pests and diseases, increasing tillering and dry matter production of the aerial part and roots, in addition to increasing the number of full grains and grain weight (HARTARI et al., 2018).

Iron toxicity in irrigated rice

          Flooding of the soil promotes the solubilization of iron, which can lead to the accumulation of the Fe ion. 2+ in the soil solution and reach levels toxic to rice. Table 4 presents an interpretation of the probability of occurrence of iron toxicity in the crop, based on the iron content extracted in ammonium oxalate solution pH 6.0.

Table 4- Interpretation of the risk of occurrence of iron toxicity according to the percentage of CTC saturation (PSFe2+).

          The use of tolerant cultivars is the most economical and efficient way to control the problem. Prior liming of the soil and fertilization (nitrogen and potassium) can also minimize it. 

Sulfur

          Soils far from industrial areas, with low organic matter and clay contents and intensively cultivated with irrigated rice are potentially susceptible to sulfur deficiency. In this condition, characterized by sulfur (S) content in the soil less than 10 mg/dm3, there is a positive response in crop productivity to the application of the nutrient. The application is limited to 20 kg of S/ha.

dryland system

          Nitrogen has a high demand in this system, just like in irrigated systems, since rice is a grass and therefore requires a high demand for N.

Table 5 – Nitrogen requirement for rice crops.

          Apply 10 kg of N/ha at sowing and the remainder as top dressing at the beginning of tillering, approximately 40 days after emergence. Nitrogen top dressing can be partially or totally suppressed, depending on climate conditions.

Table 6 – Phosphorus and potassium requirements for rice crops.

          The production system to be adopted, the environmental conditions for cultivation, and the expected production estimate are factors that determine the correct fertilizer management for rice crops, which is an important factor for production yield and financial return.

ILSA fertilization suggestion for increased productivity

          ILSA Brasil has a complete line of fertilizers for soil and foliar application capable of meeting all the nutritional requirements of rice crops. In soil preparation, the GRADUAL MIX line of organomineral fertilizers® provides nitrogen, phosphorus and potassium which are combined with the AZOGEL matrix® which promotes greater absorption of mineral nutrients, increased biological activity of the soil and still has a low environmental impact. Still thinking about the initial development of the crop, for seed treatment ILSAMIN Radix® It provides amino acids, humic substances, nitrogen and organic carbon that enhance root development, which will promote greater use of water and nutrients by plants.

          As we saw in the text, nitrogen is the nutrient extracted in the greatest quantity by the crop and has a direct influence on all components of rice yield. Thus, the most efficient supply of nitrogen promotes higher productivity, allowing the crop to express its genetic potential. For the most efficient supply of nitrogen, count on AZOSLOW®, organomineral fertilizer that combines in a single pellet the organic matrix AZOGEL® rich in organic nitrogen and carbon and amino acids with mineral nitrogen that will be quickly made available to the plant. The application of AZOSLOW® should be carried out as a top dressing and divided into two moments: 50% of the dose in the vegetative phase V3-V4 and 50% of the dose at the beginning of panicle differentiation, in cultivars with a longer cycle this division can be carried out in three moments: V3/V4 – V6/V7 – R0/R1.

          ILSAMIN AGILE® provides amino acids from the GELAMIN matrix® that promote increased plant resistance to abiotic stresses during their production cycle. In this way ILSAMIN ÁGILE® can be applied via foliar application throughout the crop cycle. ETIXAMIN KALLY®, water-soluble fertilizer for foliar application is obtained from the combination of the GELAMIN matrix® with mineral sources of potassium and sulfur. Its application in rice crops is indicated at the time of grain filling, since potassium plays a fundamental role in this process, as this nutrient will transport photoassimilates from the vegetative structures of the plant to the grains.

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 Authors

Agr Eng. Dr. Angélica Schmitz Heinzen

Agricultural Eng. Msc. Carolina Custodio Pinto

Agricultural Eng. Msc. Thiago Stella de Freitas