-Why it’s crucial for growers to stay on top of their fertilizer and irrigation schedules.-
Some of you may remember the joke from Pulp Fiction that Mia (Uma Thurman) told Vincent (John Travolta) after their disastrous dinner date.
Three tomatoes are walkin' down the street. Papa Tomato, Mama Tomato and Baby Tomato. Baby Tomato starts lagging behind, and Papa Tomato gets really angry. Goes back and squishes him and says: "Ketchup." Ketchup.
In the past few months, I’ve had several inquiries from growers about “catching up". Catching up with fertilizer or irrigation on their crops. Just like baby tomato who fell behind, they fell behind on their fertilizer and irrigation schedules and asked me about applying more to catch up.
Making plans for nutrients and irrigation is essential for a successful crop. Sometimes our plans get derailed. Rain can continue late into the spring preventing fertigation applications on your almonds. An irrigation well could stop pumping due to a failed casing during a week of hot weather in July, when you had planned to apply 2.15 inches of water per acre. Should you apply extra fertilizer once you're able to start your fertigation schedule so you can catch up with your planned nutrients? Should you apply extra water and catch up with your missed irrigation when you find another irrigation source for the field with the failed well?
Generally, no. You cannot compensate for the time period already passed. The crop’s demand for nitrogen or water for that missed week(s) has passed. The crop won’t absorb more nitrogen or water than its current demand.
If your fertigation plan called for all nutrient applications to be applied by June 1st and you started late because of heavy March rain, and got even further behind when it rained for 2 weeks in May, can you fertigate 3 times your normal weekly nutrient amounts the last week of May? I have seen two instances where this was the case. In both instances the result was dead trees. And in both cases, a high rate of fertilizer was injected into the irrigation system in a short period of time. I’m referring to an injection time of 20 to 40 minutes. While this may be convenient for fertigators, the distribution uniformity is very low and the chance for toxic amounts of fertilizer near the injection point increases. It’s better to inject the fertilizer over a 4 to 6-hour period (or longer) at slower injection rates. You can find good information in the ANR publication 21620, Fertigation with Microirrigation.
Irrigation runs or amounts can be disrupted for various reasons. An almond grower discovered a faulty valve was applying ½ the water he planned to apply. The other ½ of the water was being applied to the other set. So, while both sets were being irrigated and everything looked normal in the spring, one set was getting less water than its demand. It took 6 weeks for this to show in the tree growth and the problem with the faulty valve was found and corrected. The grower tried to catch up by putting more water on the set that was unintentionally deficit irrigated. Did it work? Of course not. The trees demand was not met for 6 weeks and the result was less shoot growth, earlier harvest and less yield (250+ lbs/acre) than the over irrigated set.
One more example. Almond harvest is a challenging time for irrigation. A grower decided he did not have time to irrigate between varieties and by the time he finished harvest of both varieties, 25 days had passed since his last irrigation. As you can imagine, the soil and trees were very dry. So, to catch up on moisture, he irrigated with his microirrigation for over 90 hours. That’s almost 4 days. He achieved his goal of getting plenty of moisture in his trees. Too much as it turns out as in the spring, he had dozens of trees with root infections and crown rot.