Cool Season Grasses
Success of winter pastures depends on rainfall. This is especially true when overseeding. When winter forage is seeded, grazing generally becomes available mid to late December. However, it is dependent on the time of planting and weather conditions, particularly adequate soil moisture. Deferred grazing, hay, feed concentrates, and other supplements are often needed to support livestock throughout the winter months or until winter grazing is established.
In central and south peninsular Florida sod seeding (overseeding) of cool-season annuals into a established grass sod often fails due to insufficient soil moisture and this is generally not recommended unless irrigation is available. Dry conditions can be exacerbated during La Niña seasons. On the other hand, El Niño phases tend to be rainier than normal, thus facilitating good establishment.
In south central Florida, small grains and ryegrass have been successfully grown on flatwoods in late October through early November. It is important to note that the further south one goes in Florida, stronger are the winter and spring effects of El Niño/La Niña events. This means that La Niña winter and springs are not only drier, but also hotter than normal. Planting winter annual forages under such conditions may be risky.
Warm Season Grasses
Warm-season forages are planted at the start of the warm season (spring and summer). Soil moisture is usually the most critical factor in determining when to start planting and whether establishment will be successful. Always plant in a moist seedbed and at the time of year when sufficient soil moisture can be expected to continue for 10 to 12 weeks. These conditions may be especially prevalent in El Niño springs. Planting a perennial grass in April in south Florida is not a good idea because of the expected April/May drought. This would be even less advisable if La Niña were forecast. On the other hand, El Niño-La Niña anomalies have little effect in summertime in the southeastern United States; thus, summer plantings are more weather- than climate-driven.
Most of the warm-season perennial grasses are planted in late winter or at the beginning of and during the rainy season (June-August). In late winter, El Niño can bring much needed rain that aids in pasture establishment. When La Niña is forecast, however, late winter plantings are a high risk. Climate considerations for June-August plantings depend more upon historical records (climatology) and short-term weather forecasts because El Niño and La Niña have little measurable effect during the summer months.
Late-winter and spring planting of dug sprigs is mainly done in north Florida, where the chances of a severe spring drought are less than in south Florida. The chances are nevertheless high for a drought when La Niña is forecast. Most planting of vegetative material in south Florida is done during the summer rainy season and is therefore independent of El Niño or La Niña influences.
Fertilization
Nitrogen and potassium can be leached from sandy soils by heavy rainfall. This is especially typical of El Niño years. If this occurs, it may be desirable to apply more N and K as an adjustment to leaching or to use smaller but more frequent applications in an attempt to minimize leaching losses.
Warm-season perennial grasses should be fertilized in February to March. La Niña forecasts mean dry weather during this time of year and grasses may show little response to fertilization. Limpograss, rhodesgrass, and stargrass can be fertilized in the late summer or early fall. Summer applications are not influenced by seasonal climate variability forecasts. The response obtained from an application of fertilizer is influenced by many factors such as solar radiation, temperature, soil moisture, and grazing management.
Adequate soil moisture must be available either from rainfall or irrigation for these crops to prosper. In southern Florida, lack of adequate rainfall during the cool season frequently causes stand failure or limits growth. These conditions tend to occur when La Niña is forecast. During El Niño phases, wetter conditions favor legume establishment. Under non-irrigated conditions in southern Florida, the probability of inadequate moisture is high and the likelihood that the crop will benefit from applied fertilizer is low, especially on drier soils.
Temperature and Forage Quality
Plants grown at high temperatures generally produce lower quality forage than plants grown under cooler temperatures, while cool-season species grow most during the cooler months of the year. However, forage of any species tends to be lower in quality if produced in a warm region rather than a cool region. In general, it can be said that forage will be of a lower quality during La Niña phases and higher during El Niño phases. Research should be conducted to see if these differences are significant enough to merit management changes.
Stocking Rate
Stocking rate is one of the most important decisions that a pasture manager makes. The ideal stocking rate in a given situation is affected by the forage, weather conditions, fertilization, amount of concentrate being fed, and production goals. When drought conditions hit, stocking rates are much less. During La Niña, pastures may only be able to carry around 12-15% less than during normal years. Winter pastures carry fewer animals; in many cases, between one and two animals less per acre. Late fall through spring are critical periods when more forage may be needed. It is during these seasons that La Niña effects are felt hardest, especially in peninsular Florida.
Making Hay
In northern Florida, southern Alabama, and southern Georgia, hay can be harvested throughout the growing season during most years. In southern Florida, hay can be harvested in the spring before the summer rains start, if there is sufficient growth, and in the fall after the summer rains stop. Growth may not be enough to merit cutting in La Niña springs. Conversely, El Niño springs typically produce high biomass. In South Florida, many producers apply fertilizer from mid-August through mid-October to hay fields, with harvesting in November or December after the rainy season has ended. An El Niño fall might prevent good hay from being made because conditions will tend to be wetter than normal.
Pasture Renovation
Renovation programs are usually started in the spring or fall. Therefore, they are potentially influenced by seasonal variability forecasts. Remember, effects tend to be strongest in winter and spring. One strategy that is especially useful in peninsular Florida is to plow and disk during the months of April and May - usually a dry period. However, if El Niño is forecast, too much spring rain may keep plants from desiccating. The old sod may be plowed in the fall (November-December) and then planted with the desired species in late winter or early spring. El Niño springs are likely to produce proper wet conditions for success in planting.
Nitrogen Leaching and Forage Crops
Perennial pastures such as bermudagrass and bahiagrass are in general good options to protect N from leaching to groundwater because of the dense root system they form, the stability they confer to the soil, and their high capacity of N uptake. Bermudagrass was a better N up-taker and higher biomass accumulator than bahiagrass. However, these two crops have a dormant period (winter) and are not considered as good as some other crops for feeding dairy cows. When present these grasses must be inter-cropped or sod-cropped with at least some winter forage. Bermudagrass and bahiagrass could also be over-planted during summer season with corn or sorghum for a more intense production system that will uptake more N. This could be a good strategy for neutral summers. When including a summer crop in the pasture, it is important not to destroy the pasture with the field preparations for the other crops.
Corn, sorghum, and millet are good N up-takers, good biomass accumulators, with medium N leaching. They can be planted in summer and/or fall during any of the ENSO phases.
Winter forages including oats, wheat, rye, ryegrass, and others, are in general low biomass accumulators and present a medium to high N leaching risk. In critical years such as El Niño years, inter-planting some or all of these crops (not uncommon) is recommended. These winter annuals will provide maximum N