CHARACTERIZATION OF PRUNE AND WALNUT ORCHARD SOILS FOR WATER INFILTRATION IMPROVEMENT POTENTIAL

Transcription

1 CHARACTERIZATION OF PRUNE AND WALNUT ORCHARD SOILS FOR WATER INFILTRATION IMPROVEMENT POTENTIAL Michael J. Singer, John R. Munn Jr., William E. Wildman ABSTRACT Characterization of nine soils from the Sacramento and San Joaquin Valley continued in Particle size distribution, ph, organic carbon, extractable bases, acidity, cation exchange capacity, liquid limit, plastic limit, saturation moistur~ percentage, electrical conductivity of the z sa~uration _ extra~~, Ca 2.1 Mg, Na, K, HC03, Cl, F, NO, N03, P04, S04 concentrations' in tne saturation extract, ana quantitative clay mineralogy were determined for the nine soils. Percentage base saturation, exchangeable sodium percentage, sodium adsorption ratio, and plastic index were calculated. Additional characterization data are being collected. Preliminary data analysis indicates a range of physical, chemical, and mineralogical properties for the different soils which may be related to slow water penetration. For example, the Wyman soil has 0.54% organic carbon, 4.8% exchangeable sodium, low total clay content and low expanding clay percentages. These characteristics increase the likelihood of breakdown of surface structure with subsequent crusting and surface sealing when high quality water is used for irrigation. This problem can be partially alleviated by adding organic matter or soluble salts to the soil to improve aggregate stability and to decrease the influence of sodium. Results from an infiltration trial on the Wyman soil in Yuba County where phosphogypsum at a rate of 1650 lbs/ac was added to improve water infiltration showed that the plots with gypsum had infiltration rates of 0.08 in/hr compared to 0.07 in/hr for untreated plots. In this case, the rate of gypsum application was apparently too low to substantially improve water penetration. OBJECTIVES 1. To collect samples of important prune and walnut orchard soils, with and without water infiltration problems, and determine for these, the physical and chemical characteristics that contribute most to surface sealing, soil compaction, and slow water infiltration, taking into consideration the interaction of these characteristics with various irrigation water qualities. 2. To develop criteria for predicting the likelihood of improving water infiltration in these orchard soils by use of the following practices: (a) a change in irrigation management or method; (b) clean cultivation vs. annual cover crop or permanent sod; (c) ripping or slip plowing between trees; (d) applying amendments to the soil or irrigation water. PROCEDURES Laboratory: Soil physical, chemical, and mineralogical characteristics which may influence aggregate stability and water penetration were selected for determination by standard laboratory methods

2 Field: On June 30 and July 1, 1982, a six plot trial of phosphogypsum as a possible amendment was established on the Fred Shaeffer ranch in Yuba County. The six contiguous plots were in a portion of a mature prune orchard. Each plot was 9 x 3 trees (0.18 ac). Each of three plots was treated with 300 pounds (165b 1bs/ac) of phosphogypsum prior to an irrigation. Irrigation water was applied by flooding the plots for 3~ hours. Water depth was measured at various times over the following 22~ hours. An initial infiltration rate, and a final percolation rate was calculated for each plot. RESULTS AND CONCLUSIONS Laboratory: Particle size distribution for the nine test soils indicates that all of the soils are medium to coarse textured (Table 1). Only two, the Verna1is and Yolo have over 20% clay. All but the Wyman have over 30% silt, and all but Wyman and Ryer have over 35% silt. Each soil has a unique sand fraction distribution. At the extremes are the Columbia soil with 53.4 of the sand fraction as fine and very fine sand and Wyman with ~4. 4% of the sand fraction as coarse and very coarse sand. The significanct:: of particle size distribution on water penetration is not clear because several of the soils with quite different particle size distributions appear to have similar infiltration rates. The chemical characteristics of the nine soils are more uniform than the particle size distribution,but some apparent differencesdo exist among the soils (Table 2, 3, 4). Organic carbon is less than 1% in six of the nine. Note that the Wyman soil from the Shaeffer ranch is lowest of all. Poor aggregate stabili ty is often equated with low organic carbon content. The only other data from Table 1 which are notable at this time are the 4.5 and 4.8 percent exchangeable sodium percentages (ESP) values of the Sorrento and Wyman soils. These values are well below the 15% considered high by the U.S. Salinity Laboratory, but they are at a level which could lead to clay dispersion in orchards where high quality irrigationwater is used and the soil has a low ability to release soluble salts. Sodium content is also reflected in the SAR of the saturation extract of the Wyman soil (Table 3). Atterberg limits are the only "physical" properties measured thus far. These engineering test data are useful as an index of the moisture content over which the soils will be susceptible to compaction (Plastic index) and the moisture content at which the soil loses most of its ability to support loads. Thus the Wyman, although plastic over a very small range of moisture contents, loses strength at a low moisture content and is thus susceptible to severe compaction problems when wet. Tables 5 and 6 summarize the clay mineralogydata for the soils. We have not completed the interpretation of these data in terms of the mechanisms through which the clays may affect crusting and sealing. It is clear that the soils differ in their qualitative (Table 5) and quantitative (Table 6) clay mineralogy. Two examples are sufficient to illustrate the diversity and possible importance of the clay mineralogy to the problem of water penetration. The Verna1is soil has a large proportion of smectite and intergrade clay minerals which will shrink and swell with changingwater content, thus forming aggregates and, when dry, cracks, that allow some water penetration. In

3 contrast, the San Joaquin soil is dominated by non-expanding, Kaolin clay minerals that do not readily form soil aggregates or surface cracks.- Additional work is required to complete the characterization of the soils and interpretation of the data. Part of the characterization that is needed is a quantitative measurement of salt release and crust formation in these soils. Field: There was a large increase in initial water penetration rate for the gypsum plots compared to the control plots (Table 7). The final w~ter penetration rates were only slightly different. Two factors may help to explain these results. First, previous work by Bill Wildman showed that the ripping done at this site in past years to break up a well developed plowpan quickly lost effectiveness. Thus some of the reason for slow water penetration may be subsoil density. Second, the laboratory data indicate a low salt release relative to exchangeable sodium percentage for this Wyman soil. The rate of phosphogypsumapplication (1650 lbs/ac) may have simply been to low to show a positive effect on infiltration rates. In the future, laboratory studies to determine the appropriate amendment rates, and field studies to determine the effect of deep ripping will help to solve the problem of slow water infiltration in California Prune and Walnut Orchards. pjl:12/6/82dw 104

4 table I. Particle She D18tr1butlon of te.t Sotl.. 'ARTICLE SIZE DISTRIBUTION USDA V.Co.Sand Co..and H. Sand F. Sand V.f..and Toul..nel Coarse silt Hedina 81It fine 8ilt toul stlt Co. clay 1 Co. Clay 2 N. & r. Clay Tvt.l Chy Seri. TeJl:ture (2 to 1_) (I to....) (. to.2...) (.2 to.1...) (.1 to.o_) (.2 to.o_) (O to 10um) (20 to um) ( to 2U8) (O to 2uII) (2 to lull) (I to 0.2uII) (0.2U8) ( 2 um) I t Columbi. vrsl Ryer L B San Joaquin L I B to-' 0 Sorrnto L 0.2 O & VI # Vernal1s CL I Vine L I. I WYllan CoSI B Wyo L B I Yolo SlL

5 Table 2. Organic Carbon, Extractable Cations and Acidity, Cation Exchange Capacity, Base Saturation, Exchangeable Sodium Percentage and ph for the Test Soils. Extractable Cations & Acidity Ca Mg K Na Acidity EC+EA CEC Soil OC meq/ meq/ meq/ meq/ meq/ meq/ meq/ Base ESP ph ph Series % 100g 100g 100g 100g 100g 100g 100g Sat. (%) (%) Sat.Paste 1:1 Columbia Ryer San Joaquin Sorrento (J\ Verna1is Vina Wyman Wyo Yolo sum of cations Percentage base saturation = CEC x 100

6 Table 3. Chemistry of the Saturation Extract Solution for the Nine Test So11s. Solution Cations Solution Anions - - NO - NO - Anions SAR Water ++ Tota 1 rotl Content ECI Ca Hg K Na Cat ions IICO - CI F PO -3 SO -7 Series 1; (mmhos/cm) (meq/l) (meq!1) (meq/l) (me'll 1) (meq!1) (meqh) (meq/l) (meq/l) (meqh) (meq1t) (mcqll) (me/l) (m.q/l) J Columbia , Rycr , I 0.53 Sn Joaquin S(lrrento V..rna 11s I. 54 \'ina Wym.l n Wyo \", I. 29 IElcctriralconductivity

7 Table 4. Atterberg Limits of the Nine Test Soils. Atterberg Limits Soil Liquid Plastic Plastic Series Limit Limit Index Columbia NP Ryer San Joaquin NP Sorrento Verna1is Vina Wyman Wyo Yolo

8 Table S. Summary of X-Ray Diffraction Analyses, 2.0 ~m Fraction. Soil Series/Mineral Abundance Mineral Columbia Ryer San Joaquin Sorrento Vernalis Vina Wyman Wyo Yolo Kaolin Mica Vermiculites Smectites Chlorite \0 Chlorite-Vermiculite Intergrade??????? Chlorite-Smectite Intergrade? ??? Undifferentiated Intergrades Chlorite-Vermiculite Interstratified ++?? ++ Chlorite-Smectite Interstratified?? ++ Vermiculite-Smectite Interstratified?? Mica-Vermiculite Interstratified Undifferentiated Interstratified Relative Abundance: ++ = presence apparent, ++++ = presence dominates other peaks,? = can't specifically differentiate.

9 Table 6. Summary of Quantitative Clay Mineralogy. Soil Series Clay Components (%) Vermiculite Smectite Non-Exp. Whole Soil (%) Vermiculite Smectite Non-Exp. 110

10 Table 7. A Comparison of Initial and Final Water Penetration Rates from a Field Trial on the Wyman Soil. Plot No. Treatment Initial Final 1 Gypsum Control Control Gypsum Gypsum Control Mean Gypsum Values Control not measured 111