Potassium Fertilizers Injected Through Three Drip/ Microsprinkler Irrigation Systems Compared To Broadcast Applications On Almonds

Dr. Roland D. Meyer
University of California - LAWR Dept.

J. P. Edstrom

L. J. Schwankl
& Nickels Soil Laboratory

Objectives:

Problem and its Significance:

High yielding almond orchards with declining leaf potassium levels on the West side of the Sacramento Valley and other areas of the state have given growers cause for concern regarding how best to apply potassium. The irrigation of almonds is accomplished with a number of different systems that may apply the necessary water to a very limited soil volume or wetted area up to flooding the entire soil surface and wetting all of the soil. Fertilizers may be applied to the soil surface in a band or broadcast before irrigation or winter rains, or through the irrigation system to help move the materials into the soil. If added through a low volume or smaller wetted area system, even potassium fertilizers which are not easily moved in soils have been taken up readily by trees. Some fertilizers are not dissolved easily or water quality characteristics prohibit trouble free injection into irrigation systems. Growers choose to apply potassium fertilizers on the soil surface in a band 3-4' from the tree row as an alternative. The availability of several new formulations of potassium sulfate, phosphate and thiosulfate make it easier to inject into irrigation systems. Potassium chloride is the most economical source of potassium but the addition of chloride represents a potential detrimental effect. Given the different types of application now being utilized, it seems prudent to evaluate the relative efficiency of potassium uptake from several sources, rates, and methods of placement under three of the more typical low-volume irrigation systems.

Experimental Procedures:

The Butte and NonPareil rows of the irrigation system comparison trial on the Marine Avenue location of Nickels Soil Laboratory were used for the study. The soil at the site is an Arbuckle gravelly loam (Fine-loamy, mixed, thermic Typic Haploxeralf) having a pH of just below neutral (~6.7). The potassium sources potassium sulfate, chloride, thiosulfate and mono-potassium phosphate are being compared as injected through three irrigation systems (single and double line drip and micro-sprinkler) versus higher rates applied on the soil surface as bands 3-4 feet from the tree on both sides of the tree row. Potassium chloride is the most economical source of potassium but the addition of chloride represents a potential problem in some orchards. A preliminary experiment with 9 rates of KCl (0 to 1 lb K₂O/tree/application with 4 applications per season) indicated no toxicity (see Proceedings Almond Research Conference, December 3-4, 1996 and March 31, 1997 Annual Report to the Almond Board) and was therefore included in the study at 1/4 of the highest rate. Each individual plot size is 5 trees with a 16 feet in-row spacing and 22 feet between rows in a "diamond" arrangement (124 trees/A). There is a total of 72 individual plots each having 5 trees in this experiment. Tree circumference measurements were recorded for each tree and the five tree plot totals were ranked from low to highest for each of the three irrigation systems and used to establish the two or four blocks or replications. Treatments listed for each of the three irrigation systems were then randomly assigned. Since there was an uneven number of plots for the three irrigation systems, the trial was initiated with the following treatments and replications: (1) single-line drip has 9 treatments and 4 replications, (2) micro-sprinkler has 12 treatments and 2 replications and (3) double-line drip has 6 treatments and 2 replications (Table 1). Several higher rates are included in the micro-sprinkler treatments because the wetted soil area is larger. Liquid K₂SO₄ is applied as Great Salt Lake ESP (1-0-8), potassium thiosulfate (KTS) is a liquid 0-0-25, mono potassium phosphate (MKP) is a dry granular material added to water, and KCl is dissolved in water to apply as a liquid. Liquid fertilizer injection units were designed, built and installed the summer of 1996 to inject fertilizer for each 5-tree plot. The two main irrigation systems, one for the drip (both single and double line) and one for the micro-sprinkler, are turned on approximately 1 hour before any fertilizer is injected to improve the uniformity of application. Dry granular potassium sulfate (0-0-50) is applied on the soil surface in a band 3-4 inches wide approximately 4 feet from the tree on both sides of the tree row in the fall of the year (November-December). These band applications of potassium sulfate represent normal grower practice. Injection treatments were applied in July, August, September of 1996, May, June, July of 1997, and June, July of 1998 and 1999 with the higher rates being split into 3-4 applications. Leaf samples were taken on April 4, July 7, and October 7, 1997; April 2, July 7, and October 8, 1998; as well as March 31, June 29, and October 12, 1999 to evaluate nutrient concentrations. Yield data was collected on August 27, (NonPareil) and September 23, 1997 (Butte); September 22, (NonPareil) and October 9, 1998 (Butte); as well as September 20, (NonPareil) and October 4, 1999 (Butte) to determine treatment effects. The 1996 data represent the baseline meat yields prior to any potassium treatment effects (Table 1).

Results and Discussion:

Meat yields in 1997 were significantly different between treatments under the micro-sprinkler system but there were no significant differences between treatments in the single or double line drip irrigation systems (Table 1). There was a consistent trend for all potassium treatments to give higher yields than the control. Yields did not show a consistent trend as rates of applied potassium were increased, particularly with the injected potassium sulfate (K₂SO₄) and mono-potassium phosphate (MKP) sources. It is interesting to note that the banded potassium sulfate (K₂SO₄) treatments under the micro-sprinkler resulted in good yields compared to other sources and rates whereas the banded treatments did not yield as well under the single or double line drip systems. This would be expected since the irrigation water was not wetting the area where the potassium had been applied. Only winter rains would have wetted the soil and provided for some uptake of potassium early in the spring.

There were significant differences between the 1998 meat yields for treatments in all three irrigation systems with one or several of the mono-potassium phosphate (MKP) treatments resulting in the highest yields and the banded K₂SO₄ treatments having among the lowest yields (Table 1). There was no clear trend for all of the potassium treatments to have a higher almond yield than the control. The control (no potassium applied) treatment yields for each of the three irrigation systems were slightly above (single and double line drip) or below (micro-sprinkler) the average yields for all plots under each system. As was the case in 1997, yields in 1998 did not show a consistent trend as rates of applied potassium were increased.

Yield results in 1999 indicate either a strong trend or a significant increase in response to potassium applications (Table 1). There was a slight trend for yields to increase as rates of applied potassium were increased but most of the increase came from the 1 lb K₂O/tree rate or 124 lbs K₂O/acre for four annual applications. Considering the four potassium sources, the mono potassium phosphate or MKP give the highest yields followed by the injected potassium sulfate, the potassium chloride and the potassium thiosulfate. The banded potassium sulfate treatments gave good yields under both the double-line drip and the micro-sprinkler irrigation systems but the single-line drip treatments were only slightly above the control.

Average yields in 1999 for the three irrigation system treatments were nearly the same: 2820 meat lbs/A for the single-line drip, 3152 meat lbs/A for the double-line drip and 3043 meat lbs/A for the micro-sprinkler. The 1998 average yield of 2762 meat lbs/A for the micro-sprinkler irrigation treatments was significantly higher than the double line drip irrigation treatments of 2412 meat lbs/A and the single line drip irrigation treatments of 2377 meat lbs/A. Average yields for the three irrigation systems in 1997 were as follows: micro-sprinkler 2661 meat lbs/A, double-line drip 2445 meat lbs/A, and single-line drip 2379 meat lbs/A. Average yields in 1999 for the two varieties were 2978 meat lbs/A for NonPareil and 3032 meat lbs/A for Butte. The 1998 average yield for the NonPareil variety was 2284 meat lbs/A and for the Butte variety 2791 meat lbs/A. In 1997 the average yield for the NonPareil variety was 2213 meat lbs/A and for the Butte variety 2763 meat lbs/A.

Potassium leaf concentrations in the July 7, 1997 samples were generally in the adequate range but several were below 1.25% (Table 2). Leaf potassium levels generally reflect potassium fertilizer availability as April leaf levels were fairly high for all banded treatments but dropped to quite low levels in the July leaf samples for the single and double line drip systems. Potassium leaf levels were among the highest for the banded treatments under the micro-sprinkler irrigation system. As might be expected, potassium chloride (KCl) increased potassium concentrations in the leaves but chloride levels were also increased. The highest concentration observed was near 0.2% under the micro-sprinkler system. It should be pointed out however, that concentrations exceeded 0.4% last year in the potassium chloride rate study without any leaf burn or observed toxicity to the trees. There was a trend for phosphorus leaf concentrations to be increased in the July 7 samples from the MKP treatments under all irrigation systems with a significantly higher level recorded under the double line drip system.

April 1998 leaf potassium concentrations were somewhat inconsistent with respect to rates and sources of applied potassium under the three irrigation systems (Table 3). Only the control treatment (1.54%) under the single line drip system and the 2 lbs K₂O/tree K₂SO₄ treatment (1.58%) under the double line drip system had somewhat lower leaf potassium levels than most other treatments. The July samples indicated a significant increase in leaf potassium concentrations for all sources and rates under all three irrigation systems over the controls. This was most evident under the micro-sprinkler system where 9 out 12 treatments had leaf potassium levels greater than 2.00%. The average leaf potassium concentrations for the three irrigation systems were 1.68% for the single line drip, 1.73% for the double line drip, and 2.12% for the micro-sprinkler. Leaf potassium levels were consistently increased as the rate of applied potassium for each source was increased under all three irrigation systems. The October samples indicated nearly the same significant increases or trends as did the July samples. Leaf potassium levels were consistently increased as the rate of applied potassium for each source was increased under all three irrigation systems except for the K₂SO₄ treatments (#2, 3, 7 and 8) for the single line drip irrigation system. July leaf phosphorus concentrations ranged from 0.12 to 0.155% but there were no significant differences between any of the treatments for the three irrigation systems.

The average leaf potassium concentrations were higher on both dates March 31 and June 29, 1999 for the micro-sprinkler potassium treatments, 1.82 and 2.28% than for the single-line drip, 1.54 and 1.60% or the double-line drip irrigation system potassium treatments, 1.58 and 1.79% (Table 4). The control treatments had somewhat low to adequate potassium concentrations on the June 29, 1999 sample date with the single-line drip irrigation system being the lowest at 1.09%. As the rate of applied potassium was increased, leaf K concentrations were consistently increased under the three irrigation systems and on both sample dates. The four potassium fertilizer sources gave nearly the same leaf K concentrations on both sample dates. The banded potassium sulfate treatments consistently had among the lowest leaf potassium levels, particularly considering the rates of potassium application.

Perhaps the most consistent trend across all years is that the fall banded potassium sulfate (K₂SO₄) treatments under the micro-sprinkler and double line drip systems have resulted in relatively high leaf potassium levels compared to other sources and rates whereas the banded treatments have not had nearly as high leaf potassium levels under the single line drip system. This would be expected since the irrigation water was not wetting the area where the potassium had been applied. Only winter rains would have wetted the soil and provided for some uptake of potassium early in the spring.

Table 1. Almond meat yields for 1996, 1997, 1998 and 1999 for the fall banded versus source and rate of potassium injected through three irrigation systems experiment at Nickels Soil Laboratory.

*Potassium fertilizer treatments common to all three irrigation systems.

Table 2.
Almond leaf potassium concentration in 1997 for the fall banded versus source and rate of potassium injected through three irrigation systems experiment at Nickels Soil Laboratory.

*Potassium fertilizer treatments common to all three irrigation systems.

Table 3.
Almond leaf potassium concentration in 1998 for the fall banded versus source and rate of potassium injected through three irrigation systems experiment at Nickels Soil Laboratory.

*Potassium fertilizer treatments common to all three irrigation systems.

Table 4.
Almond leaf potassium concentration in 1999 for the fall banded versus source and rate of potassium injected through three irrigation systems experiment at Nickels Soil Laboratory.

*Potassium fertilizer treatments common to all three irrigation systems.

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Copyright © 1999 Colusa County Cooperative Extension, Univ. of California
Last modified: September 01, 2000