This new planting, pictured at the end of the first season, started out as sleeping eyes and is irrigated with drip. Young trees need to be spoon-fed nutrients, and this can be accomplished through fertigation.
Once the trees are planted in a new orchard, there’s only a limited amount of time to set up the planting to be successful, says Tim Smith, Washington State University Extension educator for north central Washington. Proper irrigation practices are essential for maximizing tree performance.
Main lines, laterals, filters, and valves should be complete before planting. Water should be available at planting, and the irrigation system should be installed as soon as possible after the trees are in the ground.
Leave the trees to heal for two or three days, and then irrigate to saturate the ground around the tree roots, Smith advises. Often, particularly when the trees are planted by machine, the soil around the roots is fairly loose, even when the soil has been tamped down. Apply just enough water to settle the ground. The trees are not using much water at this stage because they don’t have leaves.
Many growers today use a dual irrigation system with drip tube and sprinklers. The drip system can be used for fertigation, and the sprinklers allow for establishment of the cover crop and adequate water as the trees mature.
The drip system can be temporary, but is useful for the first three to four years to supply consistent amounts of moisture to all the trees, Smith said. This is difficult to do with sprinklers when the trees are on dwarfing rootstocks and have limited root systems. “The bigger the tree, the easier it is to make sure that some of the root system is adequately watered,” he said. “The smaller the tree, and the higher the odds that the uneven pattern from the sprinklers is going to leave some of the trees with an inadequate amount of water.”
Extra growth boost
A dual system costs more, but Smith said starting the trees with drip can make a big difference to tree growth, especially on replant sites. On any site, the drip irrigation always seems to give the trees an extra growth boost.
If the soil is reasonably moist at planting and you’ve irrigated the trees in, hardly any more water will be needed until the leaves start developing. Watering them won’t encourage them to grow more and, in fact, could slow them down if the ground becomes too wet and cold. Trees love moist, warm conditions but not moist, cold soil. Cold, water-soaked soils can induce yellowing of leaves. “You have to give them a chance to dry out and get some oxygen and warm up,” Smith said.
Once the trees start growing, water them every few days, increasing the frequency as the trees grow and the weather warms. Water management should be adjusted whenever shoot growth does not reach the benchmark of 0.75 to 1 inch per day.
A common mistake is to water young trees as though they are mature trees. The root system is very limited for the first two years, so the tree doesn’t have much soil volume to withdraw water from. If you’re trying to produce as much canopy as possible in the first few years in order to produce high early yields, the trees should be irrigated frequently with just enough water to replace the moisture that’s taken out of the small volume of soil in the tree’s root zone, Smith said.
“You’re not trying to drive the water in three feet deep. You’re only irrigating the top foot or foot and a half because they’re not using water lower than that.”
The planting might need to be watered daily in the height of the summer. The soil around the trunk should be visibly moist at all times during hot weather.
“Treat them as if you’re watering potatoes, beans, or any other annual crop because they don’t have much of a root system,” Smith advised. “You’re trying to encourage them to produce as much wood in the first few years, so you have to baby them along.”
Long irrigation sets can cause a chimney effect, or gravitational flow of water through the soil. The gravitational flow can pull water out of the root zone and take fertilizer into the groundwater. This can be avoided by running short sets, especially when fertigating.
Having sprinklers along with the drip system allows for the establishment of the cover crop during the first summer and will ensure adequate irrigation for the planting in future years.
“You do save a certain amount of water with the drip,” Smith said, “But water savings at the expense of tree health or fruit production is an expensive savings. We first of all want to grow a healthy crop with as much efficiency as possible.”
As growers shift from high-volume impact sprinklers to low-volume sprinklers, they may need to change how they irrigate, he said. “Make sure you know how much volume you are putting on and the interval you need, and how much pressure you need. Having more sprinkler heads per acre is important in an intensive orchard. If you’re new to it, make sure everything’s set up and you know how to irrigate with that system.”
Detailed information on how to sprinkle-irrigate orchards can be found at the Web site www.ncw.wsu.edu in the tree fruit section under “Irrigation.”
Ideally, nutrient deficiencies in the soil should be addressed before the trees are planted. Failing that, the trees will need to be spoon-fed. “You don’t take a four-month-old baby and try to feed it a pound and a half of food in the morning so it can make it through the day,” Smith said. “You feed them numerous times a day in small amounts.”
Similarly, young trees don’t need fertilizer by the handful. In a high-density orchard, that can amount to extremely high rates per acre and increase the salinity of the soil. Trees need small amounts of nutrients starting from the time the shoots are about 4 to 6 inches long and the roots are growing.
A drip system is useful for applying nutrients efficiently and uniformly through fertigation. “It’s almost like having an IV directly into every tree, as opposed to not knowing how much nutrient is getting to every tree,” Smith said.
Nitrogen is the most important nutrient. A consistent, low level of zinc and boron must be available to the trees, especially when they start growing rapidly. Once the trees have foliage, foliar zinc and boron can be applied, perhaps along with a mildew spray.