Understanding and Applying Information from a Soil Test: Part 2 – NPK

Part 1 of this series emphasized that soil testing is complementary to plant tissue testing and not a substitute in orchard management.  Considerations to ensure soil testing provides representative and useful information and interpretation of two common soil test parameters: 1) Saturation Percentage (SP); and 2) pH were also discussed.   This article will focus on the nutrients nitrogen (N), phosphorus (P), and potassium (K). Nitrogen Nitrogen occurs in soils as organic and inorganic forms and soil testing may be performed to measure levels of either. Nitrate nitrogen (NO3-N) is most commonly measured in standard soil tests because it is the primary form of nitrogen available to trees and, therefore, an indicator of nitrogen soil fertility.  However, soil concentrations of NO3-N depend upon the biological activity and may fluctuate with changes in soil temperature, soil moisture, and other conditions.  Nitrate is also easily leached with rainfall or irrigation so current soil tests may not reflect future levels of nitrogen soil fertility.  Table 1 provides guidelines for evaluating NO3-N soil fertility levels.  Table 1.  Guidelines for interpreting nitrate nitrogen (NO3-N) levels in soil test results. Fertility Level ppm lbs/acre1 Low <10 <36 Medium 10-20 36-72 High 20-30 72-108 Excessive >30 >108 1 Some laboratories report NO3-N as lbs/ac rather than as a concentration (ppm).  A soil bulk density is assumed in this calculation so the NO3-N fertility levels should be considered an estimate rather than an absolute level.   Ammonium  nitrogen (NH4-N) is also a plant available form of nitrogen in orchard soils and it can be determined with soil testing upon request.  In general, NH4-N is not determined and reported with a standard soil test.  Ammonium nitrogen does not usually accumulate in soil because soil temperature and moisture conditions that are suitable for tree growth are also ideal for conversion of

December 7, 2010

Soil Testing and Analysis: What to Expect in the Report

Agricultural laboratories usually analyze and report soil salinity and fertility levels in the same report.   Saturation percentage, electrical conductivity, sodium, calcium, magnesium, chloride, bicarbonate and carbonate, sulfate, and boron are all part of salinity.  Indices such as the Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) are calculated from these basic measurements of soil salinity and included in the report.  Soil testing for salinity is designed to diagnose osmotic effects, specific ion toxicities, and infiltration problems.  When the salinity (electrical conductivity) of the soil-water surrounding the root exceeds the tolerance of a salt sensitive crop like walnut, the gradient between the solute concentration in the root cells and the soil-water around the root lessens, reducing water availability to trees.  Trees influenced by osmotic effects will not grow as vigorously.   Specific ion toxicity involves the accumulation of sodium, chloride, or boron in soils to high enough levels that the risk of these elements accumulating to toxic levels in leaf tissue of trees increases.  Symptoms of ion toxicity may include death of leaf tissue along the margins or in the interveinal areas of leaves.  Soils that develop slow water infiltration and permeability rates are sometimes related to low levels of electrical conductivity and calcium, and high levels of sodium or magnesium. Fertility focuses on essential plant nutrients, which is evaluated based upon soil pH and proper quantities of nitrogen, phosphorus, potassium, zinc, iron, manganese, copper, and molybdenum in the soil to promote walnut tree growth and fruit development.  While calcium, magnesium, boron, and chloride are important to diagnose salinity, they are also of interest from the standpoint of fertility in terms of deficiency, sufficiency, and balances. Salts and nutrients exist in soils as three forms (see schematic) and this is reflected in soil test reports.  Bulk minerals and organic reserves release

November 9, 2010

Unusual Leaf Symptoms in 2010- Some thoughts…

Several calls have been coming in over the past few weeks regarding unusual leaf symptoms on almonds. For the most part, the symptoms have appeared across varieties, but with one variety being more heavily affected within a single orchard. Symptoms also have appeared in waves, starting about mid-April, again in May, and then again in June. Orchards all over the San Joaquin Valley have been calling in with reports, varying in ages, varieties, nutritional status, and orchard spray practices. The symptoms appear to start off as small, yellow pin-head sized lesions on the leaf (Figure 1). Following a few days of heat, the lesions enlarge, and become necrotic, often abscissing from the leaf (Figure 2). The margins of the leaf appear to be the most severely affected, with some damage evident throughout the leaf blade. Figure 1: Initial damage observed of foliar problem commonly experienced in the 2010 crop year. Photo provided by Allan James, Mid Valley Ag. Figure 2: Damage to almond leaves experienced in the spring of the 2010 growing season. These symptoms appeared later than the symptoms observed in Figure 1, usually after a hot spell. I initially thought that the problem was due to foliar nutrient sprays – either due to contaminated products or cation activation (iron, zinc, manganese, magnesium, etc.) by a rain event. This didnt seem to fit the symptoms in every orchard due to some orchard owners not spraying foliar nutrients. Symptoms also appeared similar to potassium deficiency, but the widespread occurrence throughout the valley does not support a nutrient deficiency. The possibility of corky spot was brought up, especially since the leaf symptoms look similar to the pictures of this disease. Corky spot is an unknown disorder that tends to be associated with nonpareil planted on seedling almond type rootstock (i.e. bitter almond). Due to the widespread occurrence of this symptom across differing orchard ages, nursery

July 6, 2010

Fertilizing one-year old trees – be careful!

Nitrogen is the most important element we can apply to our tree fruit crops. Almond growth and productivity depend on the availability and uptake of nitrogen. Most fertilizer recommendations are based on making nitrogen available to our trees so that a nitrogen shortage does not limit tree growth or productivity. Young almond trees don’t require as much nitrogen as older trees. I like Wilbur Reil’s rule of “one ounce of actual nitrogen per year of age of tree”. That rate can be applied several times per season, but never more than that at any one application. Thus, a first leaf (first year in your orchard) almond tree should not receive more than one ounce of actual nitrogen per any application. A five year old almond tree should not receive more than 5 ounces of actual nitrogen per one single application. The University of California only recommends one ounce of actual nitrogen per one year old tree over the course of the season, but I have been told by many growers and PCAs that this rate is not enough for the growth they desire. So, if you want to put out five ounces of actual nitrogen per one year old tree, do so in five applications and not all at once! I have seen many trees burned by nitrogen, especially if liquid fertilizers like UN-32 (urea ammonium nitrate 32 %) or CAN 17 (a clear solution of calcium nitrate and ammonium nitrate) are used in single applications. These liquid fertilizers are very effective and easy to use but it doesn’t take much to burn young trees. I do not suggest using these liquid fertilizers on first leaf trees–I prefer to see triple 15-15-15 (15% Nitrogen – 15% Phosphorous – 15 % Potassium) fertilizers used on first leaf trees. I like to

March 15, 2010

Postharvest Care for Almonds

We are mid way through almond harvest. As we finish up shaking our Nonpareils, we need to keep in mind the list of orchard tasks to help maintain crop production for the next year. For almonds, flower bud differentiation takes place during the month of September. This means that next year’s bloom and subsequent crop is being formed in the middle of this year’s harvest. During this time period, there are three important cultural practices that need to be considered by almond growers.They include irrigation, nitrogen fertilization and pruning. 1. Post-harvest irrigation is very important to keep the leaves active and functioning until normal leaf drop, which typically takes place at the end of October, early November. By preventing premature defoliation, we let the tree transition its nutrients from the leaves back to the fruiting spurs. The nutrients that are known to migrate from the leaves to the spurs at the onset of leaf fall are nitrogen, potassium and phosphorous. These nutrients play major roles in bloom development and fruit set. If the orchard does prematurely defoliate due to lack of water, irrigate to encourage re-growth. This may reduce yields in the following year, but yield loss will not be as significant as not watering at all. If watering does not occur, not only will fruit bud differentiation be poor, the orchard will suffer from premature flower drop in late winter. The best advice is to avoid this situation all together by properly managing your water during the harvest period. 2. After irrigation, nitrogen fertilization is the most important cultural practice in an almond orchard. For most of our orchards, split nitrogen applications provide the most efficient use of nitrogen. A post-harvest nitrogen application can be of 20 to 40 pounds per application – dependent upon tree age- totaling no

September 1, 2009

Mid-July Leaf Sampling for Almonds

Leaf analysis of almond is a useful tool in diagnosing deficiencies, toxicities, and future nutrient needs of the tree. It provides an up to date analysis of the mineral composition of the tree, with desirable concentration of different elements known through extensive University of California research. Reasoning for sampling. As almond trees increase in size, their demand for nutrients also increases. Tree nutrient concentration is dependent upon the growth rate of the crop and the amount of nutrients that have been supplied naturally or through fertilizer. Under certain conditions, plant tissue may become deficient which could limit further growth and crop quality. Depending upon the nutrient and level of deficiency, remediation is possible in the current season, dormant period, or early spring of the following year. Leaf concentrations of major elements (nitrogen, phosphorous, and potassium) can be used along with kernel yield per acre to determine the nutrient budget for the next season. Process of sampling. Sampling should be distributed in a regular pattern across the block, with fully expanded leaves pulled from non-fruiting spurs on branches at least 6 feet high. About 100 leaves are needed for each sample. Leaves should be picked from trees of the same variety, age, rootstock, and soil type. Trees samples should be at least 100 feet apart and 20 trees are needed to ensure accuracy and confidence with the results. Partitioning of larger sampling blocks is advised to determine tree size and yield variability. Label the samples so the sampling location is known, and keep cool until they are sent to an analytical lab. Interpreting the results. Leaf analysis results are recorded either in percentages (%) or parts per million (PPM) of each element in a given weight of dried leaves. The table below contains the critical values for almond leaves sampled in

July 13, 2009