Fenn, Lloyd B.

Gass, Willis B.

Gray, Carl

Lindsey, Kenneth E.

Welch, Charles D.

English

OAKTrust Digital Repository (Texas A&M Univ)

L·1506FIELD AND FORAGE CROP FERTILIZATION IN THETRANS-PECOS AND EDWARDS PLATEAU REGIONSCharles D. Welch, Carl Gray,Kenneth E. Lindsey, Willis B. Gass and Lloyd B. Fenn*The Trans-Pecos is an important agriculturalregion of about 18 million acres, while the EdwardsPlateau, less important agriculturally, includes about24 million acres. A large part of both regions is inrangeland, brush and rough, unproductive land.Cropping and Soil ConditionsOnly about 5 percent of the Trans-Pecos Region isused for crops. Cotton, alfalfa, grain sorghum andvegetables are the major crops grown. Irrigationmanagement, salinity, and low nitrogen and phos-phorus are major soils problems.An estimated 2 percent of the land in the EdwardsPlateau is used for cultivated crops. The main crops aresmall grains, grain sorghum and forage grasses.Shallow soils, low moisture, and low nitrogen andphosphorus are the major soils problems in this region.Soil Fertility LevelsSoil characteristics, past fertilization and croppinghave contributed to a wide range in nutrient levels insoils throughout these regions. Soil test summary datais available for some counties and is useful foridentifying general fertility problems that needemphasis in Extension educational programs.Table 1 contains the normal soil nutrient levels andpH ranges found in these two regions. Nitrogenlevels, not shown, are generally low except after afallow period following a legume, or under highnitrogen fertilization.*Respectively. Extension soil chemists. The Texas A&M Uni-versity System; area Extension agronomist. Ft. Stockton; areaExtension agronomist. Texas A&M University Research andExtension Center at San Angelo; and assistant professor.Texas Agricultural Experiment Station. Texas A&M UniversityResearch and Extension Center at EI Paso.Figure 1. The Edwards Plateau (darker) and Trans-Pecos (lighter) Regions.Phosphorus is the second most commonly deficientnutrient. Values in Table 1 show 32 and 36 percent ofthe samples from the Trans-Pecos and EdwardsPlateau, respectively, to be low in phosphorus, while61 and 46 percent were high. The latter values areespecially important because they indicate that littleor no phosphorus would be needed for crop produc-tion. Seventy-six and 100 percent of samples testedwere high in potassium in the Trans-Pecos andEdwards Plateau, respectively.Rates of N, P20S and ~OThe wide range in rainfall, soil fertility levels andcultural and irrigation management practices results ina range in rates of nutrients needed for profitableproduction. Soil tests, calibrated to express availablenutrients and correlated with crop response, are the12.13Texas Agricultural Extension Service. The Texas A&M University System. Daniel C. Pfannstiel, Director. College StationConversion FactorsFertilizers containing phosphorus and potassiumare labeled as percent P20 S and K20, and soil testvalues are reported in these terms. However, plantanalyses results usually are reported as percentages ofthe element. For this reason, the following factorsare presented for use in converting from one form tothe other.Salinity and SodiumA substantial proportion of acreage in the Trans-Pecos Region is affected by soluble salts (salinity) orsodium, possibly both. However, such problems inthe Edwards Plateau Region are limited to relativelysmall areas. In discussing salinity problems, adistinction should be made between a salt-affected(salinity or saline) and sodium-affected soils.A salt-affected soil is one that contains enoughwater soluble salt to reduce the growth of plants.Improvement generally requires the use of excessirrigation water to leach the salt below the plant rootzone. Soil salinity tests can be obtained from theExtension Soil and Water Testing Laboratory at TexasA&M University. For sampling instructions, obtain acopy of D-616 from your county Extension office.A sodium-affected soil is high enough in sodium tocause dispersion of the clay, compaction, poor aerationand other undesirable physical conditions of the soil.Improvement requires the replacement of sodium bycalcium, usually added in the form of gypsum,followed by leaching to remove the sodium. In somecalcareous soils, elemental sulfur or sulfuric acid canaccomplish the same purpose by chemically convert-ing calcium carbonate to gypsum. More time isrequired for improvement from sulfur due to the rateof the chemical reactions in the soil. However, sulfuricacid reacts rapidly and requires rapid leaching toremove sodium and excess salt.Before investing in reclamation practices for eithersalt-affected or sodium-affected soils, a thoroughstudy should be made of the problem and its causes.best guide for crop fertilizatibn. Two important criteriafor selecting the profitable rate of each nutrient are (1)the level of available nutrient in the soil and (2) theexpected or potential production.Rates ofN, P20 S and K20 at varying soil test levelsand expected yields for major crops are presented inTables 2 through 7. The soil test levels are based onTexas A&M University methods and calibrations.Unless a relationship has been estabished with othermethods, use of the suggested rates is not valid.An estimate of the expected yield should be basedon past experience, anticipated rainfall and irrigation,management, cultural practices and other factors thataffect yields. The expected yield should reflect thebest judgement of the producer and his advisors aboutthe potential for the production system.To use the tables, select the soil test level from thecolumn on the left and read across to the expectedyield column to determine the rate of the nutrient inquestion. For example, in Table 2, a soil low (L) innitrogen, medium (M) in phosphorus and very high(VH) in potassium would have a 30-0-0 and 90-30-0suggested for 3,000 and 6,000 pounds ofgrain sorghumrespectively.Calcium, Magnesium and SulfurEighty-eight and 100 percent of the samples testedfrom the Trans-Pecos and Edwards Plateau Regions,respectively, were high or very high in calcium. Somesoils in both regions contain "free" calcium carbonatewhich can contribute to iron and zinc deficiencies. Inthe Trans-Pecos Region a few soils are highly alkalinebecause of sodium.Of the samples from Trans-Pecos 97 percent weremedium or high in magnesium. All from the EdwardsPlateau 'were rated medium or high. Yield responsesfrom applied magnesium have not been reported foreither region. It is probable that the low values wereobtained from unusually sandy soils.Sulfur in soils of these regions has not been studiedextensively, but available data do not indicate it to be aproblem. Because of the relatively low productionunder dryland conditions and the fact that mostirrigation water contains some sulfate, the need forsulfur fertilization is not evident.From P20 S to PFrom P to P20 SFrom K20 to KFrom K to K20multiply P20 S by .44multiply P by 2.3multiply K20 by .83multiply K by 1.2MicronutrientsThe high alkalinity of soils in these regions causessome micronutrient deficiencies, ,principally of ironand zinc.Iron chlorosis is sometimes observed in irregularpatterns in fields of oats, grain sorghum and othercrops. More information about iron chlorosis isprovided in L-723, Identifying and Correcting IronDeficiency in Field Crops (Texas Agricultural Ex-tension Service).Zinc deficiency is common on pecan trees and hasbeen found on cotton growing in high phosphorussoils in Midland County. For more information, referto L-721, Zinc Deficiency and Fertilization (TexasAgricultural Extension Service). Although few iso-lated deficiencies have been confirmed, the extentof micronutrient problems in the Trans-Pecos andEdwards Plateau Regions is not well defined.Concern About Nutrient LossesThe objective offertilization is to apply nutrients todeficient soils for the purpose of growing plants. Therate, method and time of application should ensurethat the nutrients are used efficiently, since economicloss results from improper fertilization.Nutrients are lost or removed in four general ways:(1) erosion or movement of soil particles; (2) leach-ing of soluble nutrients; (3) denitrification or vol-atilization of nitrogen; and (4) crop removal. There-fore, good soil management and cultural practicesshould be followed to minimize erosion losses. Inaddition, nitrogen rates as well as time and methodof application should be compatible with soil condi-tions and the period of crop need.Recent studies of nitrogen application in cal-careous soils (those with free calcium carbonate) show(4) 2 NH3 + 2 H20 --....;:>- 2 NH40Hammonia water ammonium hydroxideLight-textured or sandy soils do not hold the am-monium as well as sandy loam, loams and clay soils.Because of these reactions the method of applica-tion is an important factor affecting nitrogen losses.Based on experimental data, methods of applyingnitrogen fertilizers, other than anhydrous ammonia,in order of decreasing effectiveness are as follows:BandedSurface applied and disked immediatelySurface applied and irrigated immediatelyApplied in irrigation waterSurface applied with no incorporation.Surface applications on a calcareous soil withoutimmediate incorporation should be avoided.that the chemical composition of the nitrogen fertil-izer, temperature, moisture, method of applicationand soil texture all affect the amount and rate of am-monia loss. Losses from ammonium sulfate and diam-monium phosphate can be especially large and rapid.Since losses involve chemical reactions, the rateof loss generally increases with temperature. Soilmoisture or water has a significant effect on losses.Using enough water to dissolve and carry surface-applied nitrogen fertilizers into the soil greatlyreduces volatilization losses that result from theformation of ammonium carbonate through the fol-lowing reactions:(1) (NHi)2CO + H20 ---::;~- (NHJ2C03urea water ammonium carbonate(2) (NH4)2S04 + CaC03 ,... (NH4)2C03 + CaS04ammonium calcium ammonium calciumsulfate carbonate carbonate sulfate(3) ( H4)2C03 ----=---- 2NH3 t + H2C03ammonium ammonia carboniccarbonate acidWhen these reactions take place on the surface ofthe soil, ammonia gas (NH3) can escape into theatmosphere. When in the soil, ammonia becomesattached to the negative charges on clay particles asillustrated in reactions 4 and 5.(5) 2 NH40H +ammoniumhydroxide[= ------;;;- Ca(OH)2 + H4[- claycalcium NH4 -calcium hydroxide ammoniumclay clayTable 1. Percentage distribution of soils in ranges for calcium, magnesium, phosphorus, potassium andpH in the Trans-Pecos (TP) and Edwards Plateau (EP). *Soil test Calcium Magnesium Phosphorus Potassium pHlevels TP EP TP EP TP EP TP EP Ranges TP EPVL 0 0 22 18 2 0 Below 5.0 2 0L 7 0 3 0 10 18 13 0 5.1 - 5.5 5 1M 5 0 9 6 7 18 9 0 5.6 - 6.0 6 0H 12 2 88 94 20 31 16 4 6.1 - 6.5 10 0VH 76 98 41 15 60 96 Above 6.5 77 99*130 samples for TP, 136 for EP.Table 2. Application rates of nutrients for grain sorghum.Expected yield Expected yield Expected yield3,000 Ibs./acre* 4,000 Ibs./acre 6,000 Ibs./acreSoil testlevel N P20 S K20 N P20 S K20 N P20 S K20VL 40 30 30 60 40 40 120 60 60L 30 20 20 40 30 30 90 40 40M 0 0 0 30 20 20 60 30 30H 0 0 0 0 0 0 0 30 30VH 0 0 0 0 0 0 0 0 0*Dryland; remainder under full or partial irrigation.Table 3. Application rates of nutrients for cotton.Expected yield Expected yield Expected yieldV2 bale/acre* 1 bale/acre 1V2 bale/acreSoil testlevel N P20 S K20 N P20 S K20 N P20 S K20VL 30 30 30 50 50 50 70 70 70L 20 20 20 40 40 40 60 60 60M 0 0 0 30 30 30 40 40 40H 0 0 0 0 0 0 0 30 30VH 0 0 0 0 0 0 0 0 0*Dryland; remainder under full or partial irrigation.Table 4. Application rates of nutrients for irrigatedalfalfa.Soil testlevelVLLMHVHa 160 *a 120 120 - 160a 80 80 - 120o 60 60 - 80a a aTable 6. Application rates of nutrients for small graingrazing.Dryland IrrigatedSoil testlevel N P20S K20 N* P20 S K20VL 60 30 30 160 80 80L 40 20 20 140 60 60M a a a 120 40 40H a a a a a aVH a a a a a a*Split into at least two applications.Edt.cational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-economic levels,race, color, sex, religion or national origin.Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States Department ofAgriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914.3M - 1-77 AGR 11-1

Field and Forage Crop Fertilization in the Trans-Pecos and Edwards Plateau Regions.

https://oaktrust.library.tamu.edu/bitstream/1969.1/168675/1/Leaf1506.pdf

Field and Forage Crop Fertilization in the Trans-Pecos and Edwards Plateau Regions.

Abstract

Similar works

Full text

Available Versions

OAKTrust Digital Repository (Texas A&M Univ)