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Fluid Journal : Fluid Journal 1999-2001
1 Fluid Journal Fall 2000 Summary: Summary: Summary: Summary: Summary: Potassium (K) distribution in the soil profile is characterized by decreasing soil K content with depth. We initiated a three-year study to soil apply K through a micro-sprinkler in pistachio orchards to see if it would benefit yields and crop quality and restore these K-depleted soils. Subsequent observations showed that K content increased significantly throughout the 0 to 30-inch soil profile, even though movement of surface-applied K in the soil profile was slow. Thus, more K accumulated in the fruit and leaves of the pistachio trees, appreciably improving pistachio yield and quality. In California, distribution of applied K and balance of K in the soil profile of pistachio orchards have never been addressed. Traditionally, soil K status and K fertilization requirements have been evaluated on the basis of ammonium (NH4) extractable K (referred to as exchangeable K in the remainder of this article). Soil samples are frequently taken from a 0 to 6-inch depth. However, this approach to soil K analysis may not be suitable for irrigated pistachio, since root distribution and soil moisture regime may not be well represented by exchangeable K. In micro-sprinkler- irrigated orchards, K availability in the surface soil may change rapidly due to fluctuating soil moisture in response to wetting and drying during summers, a process that may enhance soil K fixation. To accurately diagnose soil K deficiency and determine K fertilization requirements, a three-year study (1996- 1998) was initiated in two commercial pistachio orchards to determine the distribution of applied K and soil K balance in the soil profile. The orchards were located in Yolo and Madera, California, with the following characteristics or setups at the time. Soil exchangeable K K K Kinthe0to6-inch layer of soil was 156 ppm and 97 ppm, respectively. Plant density was 247 trees per acre in both orchards. Soil texture was silt loam at the Yolo site and sandy loam at Madera. Fertilization. Potassium was applied annually at one-month intervals from May to August at rates of 0, 1.1, 2.2, and 3.3 lbs/tree/year as potassium sulfate (K2S04) via a specially designed fertigation system. Equal rates of nutrients other than K were applied to all treatments. Drs. D.Q. Zeng, P. H Brown, B.A. Holtz Potassium Fertigation Improves Soil K Distribution, Builds Pistachio Yield and Quality Available soil potassium rapidly depletes in postachio orchards where it is not applied, adversely affecting pistachio yield and quality. Plots consisting of five adjacent trees were arranged in a randomized complete block design with five replications. Soil samples were collected in the fertigated zone in 6-inch increments from the 0 to 30-inch profile before and after the experiment to determine soil K distribution and balance after three years of K fertilization. Soil K increases Soil K increases SilK ncr ase olireass Soil K increases Initially, the soils had low exchangeable K, suggesting the need to apply K for adequate K supply to the trees. Potassium fertilization significantly increased soil exchangeable K over the control (Figures 1 and 2). When K was applied at the rate of 2.2 lbs/tree/year, exchangeable K in the surface 12-inch depth more than tripled following three years of K fertilization. In contrast, soil K declined sharply in control plots, resulting in further soil K depletion. Figure 1. K distribution in the soil profile after three years of K fertilization at various rates, Madera orhard, Zeng, et al., University of California. Figure 2. K distribution in the soil profile after three years of K fertilization at various rates, Yolo orhard, Zeng, et al., University of California.
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