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PT_BR 
Planting rice Irrigated farming between September and December requires planning to reduce climate risks and preserve the crop's productive potential. The choice of planting window should consider the cultivar's cycle, temperature and rainfall conditions, the availability of water for irrigation, and the infrastructure available to carry out field operations.
Correctly defining the planting season allows for positioning the most sensitive stages of rice production during periods of lower risk. This decision also helps to organize the use of machinery, labor, and water throughout the crop cycle.
Irrigated rice is more sensitive to climatic conditions during floral differentiation, flowering, and grain filling. During these stages, cold, lack of water, and excessive heat can reduce flower fertility, increase spikelet sterility, and decrease the number and weight of grains. The timing of sowing also affects water availability. Planting too late can cause the crop's highest water demand to coincide with periods of lower availability in reservoirs or greater competition for the resource.
On the other hand, planting too early can increase the seedlings' exposure to frost and low temperatures. Cold weather can delay initial development and encourage competition with weeds.
Another decisive factor is the cultivar's cycle. Early, medium, and late varieties respond differently to temperature and photoperiod. Therefore, the same sowing date may be suitable for one cultivar and unsuitable for another.
In practice, getting the planting time right means seeking favorable conditions from emergence to harvest. Emergence should occur at temperatures that favor plant establishment, while floral differentiation and flowering need to be positioned outside periods of greatest risk of excessive cold or heat.
Grain filling, in turn, depends on good availability of water, nutrients, and sunlight. Harvesting should, whenever possible, take place during periods with a lower risk of persistent rainfall, which can harm grain quality and increase losses.
To make this decision, the producer needs to combine different pieces of information. The history of minimum temperatures, occurrence of frosts, and rainfall distribution helps to identify periods of greater climate risk.
It is also necessary to consider the sensitivity to cold and the duration of the cultivar's cycle, in addition to seasonal climate forecasts. El Niño, La Niña, or neutrality trends can be used in planning to assess the risks of excessive rainfall or drought.
The availability of water for irrigation is another key point. The level of the reservoirs, the capacity of the canals, and the area that can be served by the system need to be assessed before the schedule is defined.
The machinery setup also influences the decision. Knowing how many hectares can be prepared and sown per day allows for organizing the start of operations and preventing part of the area from being planted outside the most suitable window.
The crop cycle can be divided into phases with different levels of sensitivity. In the vegetative phase, which goes from emergence to the beginning of the differentiation of floral primordia, leaf emission, tillering, and leaf area formation occur.
Very low temperatures at this stage can delay tillering and weaken plants, increasing competition with weeds. Mild to moderate temperatures, combined with good solar radiation, favor development.
The reproductive phase includes floral differentiation, stem elongation, booting, and flowering. It is the period most sensitive to cold, and low minimum temperatures can cause spikelet sterility and failures in panicle formation.
Therefore, planning aims to position flowering during a period with a lower probability of intense cold. Planting too early can cause this phase to still coincide with low temperatures.
After flowering, the grain filling stage begins, which requires adequate availability of water, nutrients, and light. Moderate and stable temperatures favor the final weight of the grains.
Lack of water or very high temperatures can accelerate ripening and result in shriveled or underweight grains. Therefore, the planting date directly influences the conditions the crop will encounter during each phase.
Frost also needs to be considered. During emergence and the seedling stage, it can cause plant death, reduce plant stand, and lead to the need for replanting.
Even minor occurrences can damage young leaves and delay development. This delay can create an environment for weeds and increase control costs.
Rain has a dual effect on the system. While it contributes to replenishing reservoirs and waterways, high volumes at the beginning of spring can hinder soil preparation and sowing.
During the summer, prolonged dry periods can make it difficult to maintain irrigation levels. Therefore, rainfall distribution needs to be considered along with water storage capacity and the available irrigation system.
Choosing the wrong planting time can reduce potential yield and increase crop costs. Excessive cold or heat during flowering can compromise productivity, while rainy and humid periods can promote disease.
Slow crop establishment can also increase weed pressure. Furthermore, replanting, additional herbicide or fungicide applications, and longer periods of machinery in the field can raise production costs.
The delay in the cycle can still hinder harvesting when ripening coincides with periods of heavy rainfall and waterlogged soils.
When planting is properly positioned, the crop can make better use of sunlight during the vegetative and grain-filling stages. Planning also helps reduce the exposure of the reproductive phase to cold and organizes the staggering of the harvest.
Between September and December, the producer can work with three situations. At the beginning of the recommended window, there is greater use of solar radiation and better distribution of water demand throughout the cycle, but there may also be a greater risk of low temperatures.
In the most suitable planting area, sowing aims to coincide with reproductive phases during periods historically less subject to intense cold. This condition tends to offer a more favorable relationship between climatic risk and productive potential.
Planting at or beyond the planting window may reduce exposure to cold during the reproductive phase, but it increases the risk of high temperatures and reduced water availability at the end of the cycle.
Late planting can also lead to harvesting during wetter periods and concentrate irrigation demand at a time of greater competition for water.
Soil management needs to follow the planting calendar. Leveling, soil correction, and base fertilization should be planned so that preparation is completed before the start of the chosen planting window.
Weed control should also be integrated into the planning. Faster crop establishment can increase soil shading and reduce initial competition, while herbicide applications should adhere to label, package insert, and agronomic prescription recommendations.
Irrigation needs to be planned along with sowing. Distributing the planting in blocks can facilitate water management and reduce the risk of water shortage during critical periods.
In larger areas, combining cultivars with different cycles and distinct planting dates can help distribute climate risks and stagger the harvest.
Planning should also consider the operational capacity of the property. If the machinery fleet has limited capacity, starting sowing earlier, within a safe range, can prevent planting from finishing at a less favorable time.
The final decision should consider the specific conditions of each property, including climate history, soil characteristics, water availability, crop cycle, and operational capacity.
Monitoring short- and medium-term forecasts can help adjust the timing of operations. For example, if very heavy rainfall is predicted, it may be necessary to assess the risk of compaction and erosion problems during preparation and sowing.
The use of treated seeds, herbicides, fungicides, insecticides, and growth regulators must follow the label and package insert instructions, as well as the requirements of an agronomic prescription when applicable.
The definition of specific planting dates depends on the region and the cultivar. Therefore, updated technical recommendations, agroclimatic zoning, and technical assistance should be considered before defining the crop calendar.
