Soil Sampling and the Effectiveness of Leaching

Unwanted sodium, chloride, and boron ions can accumulate and cause damage to the almond tree. These ions are introduced into the rooting zone through irrigation, and will remain within the rooting zone until they are either removed by the plant or leached beyond the rooting profile.

Where soil salinity is a problem, periodic soil sampling should be performed. This analysis will provide the information to determine if the salts are accumulating to a toxic level and if the applied leaching fractions are adequate. Samples should be taken from areas of the orchard showing uniformity in reduced growth or toxicity symptoms. At each sampling location, soil should be taken for each foot for the top five feet. Do not pool the soil to create a composite sample; rather, take enough samples to represent the growth differences within the orchard. The sample should also take into account the emitter patterns as differing locations may have differing salinity levels. The samples should be submitted to an analytical lab and tested for the salts of concern.

Once the results from the analysis are received, the concentration of salts at the various depths can determine the effectiveness of the applied leaching fractions. If the soil salinitity levels are the lowest near the soil surface and increase with depth, leaching is occurring. This gradient is due to the relatively low salinity of the irrigation water, the movement of salts with the water as the water infiltrates the soil during an irrigation. In contrast, if the salt levels are the highest near the surface, and decrease with depth, no leaching is occurring. The leaching fraction must be adjusted to help move soils below the active rooting zone.

Keep in mind that larger leaching fractions will result in more uniform salinity as depth increases. Inadequate leaching fractions will result in increases in soil salinity as depth increases. Water containing high amounts of salts will require a larger leaching fraction than irrigation water with low salt concentrations.

Water analysis and applying a leaching fraction for saline conditions

Written by: David Doll (UCCE Merced) and Daniel Sonke (Sureharvest, Inc).

As discussed previously, sodium and chloride build-up in soils can cause crop loss by stunting plant growth. While much of the Central Valley has access to high quality surface irrigation water through irrigation districts, many almond orchards around the state have irrigation sources of variable quality.

The first step in managing salinity is to know the source of salts. Water sources should be analyzed to determine the suitability for irrigation. Measurements of electrical conductivity (EC), sodium, calcium, and magnesium concentrations (cations), chloride, carbonate, bicarbonate, and sulfate concentrations (anions), pH, boron, and nitrate-nitrogen should be made. Most of these are standard.  Testing should occur on a regular basis since aquifer quality can change over time.

Once the data is received from the test, the data should be checked for accuracy. First, the combined totals of all of the cations and the combined totals of all of the anions should be equal. Exclude boron and nitrate-nitrogen from these calculations. Next, if the EC is 5 dS/m or less, check to see if the sum of the cations is equal to 10 times the value of the EC. If these numbers are close, but not exact, the test is of good quality with all measurements made. If the EC and sum of cations are equal, most likely one of the cations/anions were estimated by subtraction rather than direct measurement. In the case of questionable quality, re-run the sample. Waters with ECs between 5 and 20 dS/m should use a multiplication factor of 12 instead of 10.

Guidelines for water quality have been established to help identify excess salinity in water supplies. Estimating a 15% leaching fraction and the use of peach rootstocks (Nemaguard), the following table should be used as a guide to evaluate waters for suitable for irrigation and their effect on yield:

Salinity Measurement		Percent of Full Yield Potential
		100	99-40	<40
Irrigation Water (dS/m)		<1.1	1.1-3.2	>3.2

Specific ions sourced from irrigation water can also build up and cause problems. This table provides critical levels of the specified ions sourced from irrigation water. Again, these values are for peach type rootstocks (i.e. Nemaguard).

		Degree of Restriction
		None	Increasing	Severe
Sodium (SAR)		<3.0	3.0-9.0	>9.0
Chloride (meq/l)		<4.0	4.0-10.0	>10.0
Boron (meq/l)		<0.5	0.5-3.0	>3.0

Orchards with a water source that can affect yields or have an increasing or severe degree of restriction need to take salts into account especially when using drip irrigation or micro-sprinklers. The salts that make the water saline will accumulate within the rooting zone of the tree unless extra water is applied. The amount of water needed to flush the salts beyond the root zone is called the ‘leaching fraction’ or ‘leaching factor.’ For more information about the effective use of leaching to move salts and under what conditions it is recommended, see the Almond Production Manual from the University of California.

Calculating the amount to apply as a leaching fraction is dependent upon the salinity of the soil and the salinity of the irrigation water source. Using the information from the water analysis, the following equations can be used to determine the proper ‘leaching fraction’:

Here is an example of calculating the leaching fraction for an orchard with the following parameters: 2.33 net inches of water needs to be applied, the efficiency of the irrigation system is 80%, the soil EC is 4.0 dS/m, and the EC of the irrigation water is 2.0 dS/m:

Using this example, 3.69 inches of water would need to be applied to supply the needed 2.33 inches and maintain the soil EC at 4.0. The extra 1.36 inches is used to compensate for the irrigation system inefficiency and the leaching fraction. Watering less than 3.69 inches will lead to a buildup of salts and eventually to a salinity problem.

Reference: Allan Fulton, James Oster, and Blaine Hanson. Chapter 5: Salinity Measurement. Pgs 29- 40. The Almond Production Manual. University of California Agirculture and Natural Resources, Publication 3364. 1996.

Water Series by Huell Howser

Huell Howser (Thats AMAZING!) has posted a pretty good series of a rendition of his show dealing with water issues and uses throughout the state of California. Not all of them are available online, but will be shortly. Here is the link: http://www.acwa.com/content/series-segments

Might be a good way to brush up on the water systems of California.

First week in The Republic of Moldova: Initial thoughts on the Almond Industry

A little change of pace for this weeks entry:

Figure 1: Political Map of Moldova,
linked from Texas A&M.

A few months ago, I agreed to work with CNFA, a firm working with the United States Agency for International Development, as a program worker/volunteer. The assignment was to work with first time almond growers in Moldova, one of the new independent states that formed after the breakdown of the Soviet Union, to help spur economic development in the private sector The country lies between Ukraine and Romania, it is landlocked (see figure 1, map). It is considered the poorest country in Europe with a bulk of its income returning to Moldova from emigrants working abroad.

Moldova's economy is agriculturally based - it has been this way for about the last 2000 years. The major exports are wine and produce.  The country has deep, rich soils, experiences rain events all year long, has cold winters, and a high probability for a crop loss due to frost.

Over the past few days, I have had several meeting with two growers who live just southeast of the capital city Chisinau. The growers own about 200 acres, the first producing almond block within the country, grow their own trees within nursery blocks (Figure 2: Nursery block), and are looking to develop a huller for their operation. The growers have been receiving help from the local University.

Figure 2: Thats me inspecting a nursery block

They own five 40 acre blocks of varying ages with the oldest block in its fifth leaf. Trees are planted on almond seedling rootstock, spaced at roughly an equivalent of 14'x20' (4m x 6m) (Figure 3: Orchard). There are five varieties planted within the block, all developed by the local university. The trees are dryland farmed, use minimal pesticides (2 sprays with copper sulfate), and no fertilization program is established. Overall, the trees are pruned to three scaffolds and annually pruned. Their first yields on a fourth leaf block were equivalent to about 100 lbs/acre. This year's crop was lost to a late frost.

Over the next week, I will be meeting a few more days with the growers, visiting a few nurseries, and meeting with the local scientists at the University. In the meantime, I thought I would include some various observations and thoughts about Moldovan almond production.

Figure 3: 4th leaf almond blocks in Moldova

The lack of foliar diseases on all of the varieties (Figure 4: Lack of foliar diseases). All five varieties were exposed to several rain events throughout the summer, high humidity, and warm temperatures. Viewing the trees, a little brown rot and shot-hole was visible. I did not see rust or scab. This may be because of the open structure of the tree that reduces canopy humidity or varietal resistance. There is also a chance that the diseases aren't introduced to this part of Europe.

The ability for the trees to produce a crop with a growing season six weeks shorter than in California. The trees bloom in the first half of April and harvest at the end of September. I would suspect that bloom and harvest would be earlier in California.

Figure 4: One of the varieties planted
 within the orchard.

The lack of consistent nursery stock and the variability of orchard trees planted from the grower's nursery block. I never imagined the use of seedling rootstocks could provide so much variability if weaker trees were not culled prior to planting.

The ability for almond rootstocks to survive dryland farm conditions. The orchard blocks are grown on the 16-20" of water that falls naturally as rain.  Even at the denser planting scheme than traditional styled blocks, the trees were able to maintain their leaves throughout the season. It will be interesting to see if this still holds true as the trees age.

The inability of the trees to put on new growth. I would suspect that this is due to the lack of water and fertilizer. Simply a statement to address the fortunes of a relative good water and nutrient supply within California.

The lack of infrastructure, commodity organization, and marketing orders. From talking with the growers, it appears that the young industry is very cut-throat throughout the country.

Perhaps the California Industry looked similar 40,50, or 60 years ago?

Salt Burn and Stunted Growth - How Almonds Respond to Saline Conditions

Some areas of California are prone to salt damage. Within Merced County, common salt affected areas include the Livingston/Atwater/Hilmar area. The soils in these areas are coarse (Sand to Loamy Sand) and, when irrigated with well water, accumulate high levels of sodium. In other places of California, which include areas of the San Joaquin Valley and Lower Sacramento Valley,  sodium, chloride, and boron can be problematic.

Salt burn is typically identified by tissue analysis. This analysis can be through visual or analytical observations. Leaf sampling in Mid-July can be compared to UC critical values to determine the relative level of salt. Severe salt burn appears late in the summer, with leaf tips burning back. Trees severely affected can look golden in appearance and, in some cases, lose their leaves. Once salt burn is visually observed in the tree, considerable crop loss has already occurred. Annual leaf sampling can help determine if salt levels are increasing and if salt reduction strategies are needed (leaching, buffering water, etc.).

Salts dissolved in the soil water reduce growth and yield by osmotic or toxic effects. Osmotic effects are the processes that most commonly reduce growth and yield. Within a root zone unaffected by high levels of salt, the concentration of ions are higher within the root than in the soil. Through the process of osmosis, water moves from the soil into the plant. As the salinity of the soil increases, the difference between the concentration of ions between the plant and soil decreases, slowing the rate of water movement by osmosis, making water less available to the plant. To prevent this from occurring, the plant responds by making more sugars or organic acids or accumulating salts, raising the concentration of salts in the root. These processes use energy that could of been directed to the crop,  reducing growth and yield, but otherwise yielding a plant that appears healthy.

Toxic effects of salts are more noticed because of the visibility of the occurrence through scorched leaves. This occurs when salts within the soil water are absorbed by the roots and accumulate within the plant's leaves. The concentration of the salt continues to increase and eventually becomes toxic, resulting in tissue death of leaf tips and margins. Salt burn can also occur when water high in salts is sprayed onto the leaves In these cases, the salt is absorbed into the leaf through the surface, and accumulates to a toxic level within the plant cells.

Almonds planted on soils affected by sodium, chloride, and boron tend to have stunted growth and late season leaf burn. These conditions negatively affect yields, thus making the application of salinity management practices necessary.  The next few entries will focus on strategies to help reduce salt and discuss the genetic tolerance of salts amongst rootstocks.

Reference: Gratton, Stephen. 1993. "How Plants Respond to Salts." Agricultural Salinity and Drainage. Pgs 3-4.University of California Irrigation Program, University of California, Davis.