Brett Rosenzweig - Industry Development Officer In The Orchard
From this you can calculate whether the current fertigation schedule is adequate to meet crop removal needs. From the example in Table 1, 145kg of actual nitrogen was removed from the orchard in the form of the almond crop. Assuming very little nitrogen is stored in the soil and there are no cover crops planted to fix nitrogen, it would be a reasonable conclusion to state that a minimum of 145kg/ha of actual nitrogen needs to be applied the following season to replace what has been removed by the crop. Unfortunately it’s not that simple! There must be allowances made for fertiliser losses during application e.g. leaching, nitrification and nutrients being stored in the woody structures of the tree or being ‘locked up’ in the soil. Again another assumption is made that an extra 25% is needed on top of the crop removal to meet the trees nutrient needs taking into account losses and long term storage. The interaction between nutrient uptake and interactions between the soil, roots and surrounding environment is naturally very complex. The crop removal model for determining a fertiliser budget is a good starting point but should be backed up with regular soil sampling or solution sampling to ensure excess fertiliser is not being applied or leached. Calculating a fertiliser program Once you have determined how much nutrient is removed with the crop and made allowances for losses in application etc., how do you work out how many bags of fertiliser to apply? The most common types of fertiliser used in almonds are shown in Table 2. Simple calculations are made by entering the amount of kilograms of each fertiliser product by the percentage of nutrient in the product i.e. 43kg of MAP contains 11 units of phosphorus (43kg x 26%). The same can be done for the other fertiliser products to calculate the total amount of nutrient applied with the goal being to apply the same as the crop removal amount. The fertiliser program shown in Table 2 is very simplistic and other factors need to be taken into account. Is the soil temperature above 18 o C so urea or UAN can be applied? (Soil temperature needs to be above 18 o C so that it will break down into suitable forms the tree can use). Which form of nitrate (potassium nitrate or ammonium nitrate) is the cheapest fertiliser to use? In the next issue of In The Orchard, we’ll delve into how to leaf sample in October as a method of determining if the spring fertiliser program needs amending. The advantage of sampling in October is management decisions can be made proactively if the spring fertiliser program needs changing rather than reactively after January leaf sampling.
In this edition of In the Orchard, I would like to focus on post- harvest sampling of almonds to determine your crop nutrient removal status. Sampling whole fruit at harvest is a good guide to determine the base level of nutrition required for the next season. It follows a basic principle that the amount of nutrients that are removed in the form of the crop i.e. hulls, shell and kernel, should be replaced the following season to maintain equilibrium. This naturally ignores any soil reserves of nutrients that may be available for uptake and allowances must be made for losses in application and nutrients stored in the tree. Sampling How do you sample fruit to determine your crop removal status? Normally it is best to take samples immediately prior to harvest from the same trees you conduct leaf sampling from. You don’t leaf sample? A single leaf sample analysis costs only $70 (approximate, please consult your local lab or consultant) and should be conducted every year in January to gain a complete understanding of the orchard’s nutritional balance. Twenty trees should be selected in a representative manner across a patch. The patch could be a valve unit, an irrigation shift or the entire block if the property is small. Either way the area sampled should be representative e.g. don’t sample a 1Ha area with a known drainage problem when the rest of the property is 20Ha of free draining soil. Select trees that are easy to sample year after year otherwise you’ll be tempted not to regularly sample because it will become too much of a chore. If you can easily sample diagonally across a patch, this method is best. If you have to fight your way through the canopy then choose representative rows within the patch to sample. Tag both the trees and the rows that you sample from so you can come back to them year after year. Repeatability is very important when it comes to nutrition sampling. In order to detect nutritional changes in the orchard it is critical to be using the same trees each year for sampling. To sample for crop nutrient removal pick four fruit from each of your twenty selected trees to get a total of one hundred fruit per sample. Try to randomly select the fruit from all parts of the canopy, not just a small section on one branch! Separate the fruit into its three components i.e. hull, shell and kernel; making sure there are no blank or aborted kernels. Send the three samples to a lab requesting wet and dry weights along with a full analysis including boron. Results When the results of fruit sampling are received, they can be entered into Table 1. The Nutrient Removal Analysis table can be found in the irrigation and nutrition spreadsheet which can be downloaded from the Almond Board of Australia website. When the actual kernel yield for the patch is entered into the table along with the wet and dry weights of the three samples, the amount of nutrients is calculated for each of the components culminating with a total for each element. A quick point of clarification, wet weight in Table 1 refers to the weight of the crop at harvest i.e. the weight of the three samples and the kg/ha from your delivery advice. Dry weight refers to the weight of the samples after they have been dried in an oven at the lab. All leaf/ fruit/soil samples are commonly oven dried before analysis.
For further information contact: Brett Rosenzweig, Industry Development Officer Almond Board of Australia P 08 8582 2055 or 0429 837 137 E: email@example.com