&IGURE 2A. 4HE DEVELOPMENT OF SUBSOIL ACIDITY AND THE IMPLICATIONS FOR - PDF document

&IGURE 2A. 4HE DEVELOPMENT OF SUBSOIL ACIDITY AND THE IMPLICATIONS FOR ACID SENSITIVE PLANTS. As NO ACIDIC SOIL PROBLEMS. Bs ACIDIlCATION STARTS AT THE SURFACE RESTRICTING SURFACE ROOT DEVELOPMENT. Cs ACIDITY IS LEACHED TO DEPTH WHEN THE P( OF THE SURFACE SOILS DROPS BELOW 5.0 AND ALL ROOT GROWTH IS RESTRICTED. Ds 3UBSURFACE SOIL ACIDITY IS PERMANENT AS SURFACE APPLIED LIME ONLY CORRECTS ACIDITY IN THE SURFACE SOIL. &IGURE 2By 3AMPLING OF THE 10n20 CM oSUBSURFACEs SOIL LAYERo AS WELL AS THE SURFACE SOILo INDICATES WHETHER ACIDITY IS A PROBLEM IN SUBSURFACE LAYERS. hn5 028lu .162 6hl 57od574o ious loul HAVE A NEUTRALISING EFFECT ON SOIL ACIDITYo UNLESS ALL THE NITRATE IS LEACHED o4ABLE 1s BUT THEY ARE EXPENSIVE AND USE IS RESTRICTED TO HORTICULTURE. TILISER ON CROPS AND PASTURES DOES NOT DIRECTLY ACIDIFY THE SOIL. (OWEVERo ITS USE STIMULATES GROWTH OF CLOVER AND OTHER LEGUMESo RESULTING IN A BUILDhUP IN ORGANIC MATTER WHICH IN TURN INCREASES SOIL ACIDITY. ALSO THERE IS AN INCREASE IN NITRATE NITROGEN IN THE SOIL THAT COMES WITH THE HIGHER LEVELS OF ORGANIC MATTER. 4HIS INCREASES THE LIKELIHOOD OF SOIL ACIDIlCATION FROM LEACHING OF NITRATE NITROGEN. APPLYING PURE SULPHUR OR @mOWERS OF SULPHURn LIMESTONE FOR EACH KG OF SULPHUR IS REQUIRED TO NEUTRALISE THIS EFFECT. REMOVAL OF PRODUCE GRAINo PASTURE AND ANIMAL PROD UCTS AR E SLIGHTLY ALKALINE AND CONTINUED REMOVAL WILL LOWER THE SOIL P( OVER TIME. 4HIS CONTRIBUTION TO ACIDITY IS PART OF THE @CARBON CYCLEn oSEE THE GLOSSARYs. )F VERY LITTLE PRODUCE IS REMOVEDo SUCH AS IN WOOL PRODUCTIONo THEN THE SYSTEM REMAINS ALMOST BALANCED. 7HERE A LARGE QUANTITY OF PRODUCE IS REMOVED AS IN THE CASE OF HAY MAKING oPARTICULARLY CLOVER OR LUCERNE HAYso THE SOIL IS LEFT SIGNIlCANTLY MORE ACIDIC. &OR DETAILS ON THE QUANTITY OF LIME NEEDED TO NEUTRALISE ACIDITY RELATING TO COMMON AGRICULTURE PRODUCTS SEE 4ABLE 2. REMOVAL OF PRODUCE BY BURNINGo FOR EXAMPLE BURNING OF STUBBLEo DOES NOT CHANGE THE ACIDlALKALI BALANCE OF THE SOILo BUT GIVES A REDISTRIBUTIONo LEAVING ALKALI AT THE SOIL SURFACE AS ASH. )F THE ASH IS THEN WASHED AWAYo AS MIGHT OCCUR AFTER A lREo THIS WOULD LEAVE THE SOIL MORE ACIDIC. "UILDhUP OF SOIL ORGANIC MATTER OVER THE LAST 50 YEARS THE REGULAR USE OF FERTILISER AND IMPROVED PASTURESo PARTICULARLY SUBTERRANEAN 4ABLE 2. 4HE AMOUNT OF LIME NEEDED TO NEUTRALISE THE ACIDIFICATION CAUSED BY REMOVAL OF PRODUCE. 0RODUCE REMOVED ,IME REQUIREMENT KGlT OF PRODUCE -ILK 7HEAT 7OOLu 14 -EATu 17 ,UPINS 20 GRASS HAY 25 CLOVER HAY 40 -AIZE SILAGE 40 ,UCERNE HAY 70 u &URTHER ACIDIFICATION OCCURS WITH SET STOCKING OF SHEEP DUE TO THE UNEVEN DEPOSITION OF ANIMAL EXCRETA IN STOCK CAMPS. 4ABLE 3. ESTIMATES OF THE RELATIVE IMPORTANCE OF FACTORS CAUSING AGRICULTURALLY INDUCED SOIL ACIDITY FOR TWO FARMING SYSTEMS. CAUSE OF ACIDIFICATION ANNUAL PASTURE 3OUTHERN 4ABLELANDS N37ols CROPPINGlPASTURE ROTATIONo 7AGGA 7AGGA ols ,EACHING OF NITRATE NITROGEN 50n70 50n70 "UILDhUP OF SOIL ORGANIC MATTER 10n30 NIL OR REVERSE REMOVAL OF PRODUCT 10n30 20n30 5SE OF NITROGENOUS FERTILISERS NlA 5n10 CLOVERo HAS GENERALLY LED TO INCREASED ORGANIC MATTER IN THE SOIL. 7HILE INCREASING ORGANIC MATTER HAS MANY BENElTSo INCLUDING IMPROVEMENT OF SOIL STRUCTUREo IT ALSO INCREASES SOIL ACIDITY. 4HE BUILD UP OF ORGANIC MATTER WILL NOT CONTINUE INDElNITELYo AND THERE IS NO FURTHER ACIDIlCATION DUE TO THIS CAUSE ONCE THE ORGANIC USED BY A BUILD UP IN ORGANIC MATTER IS NOT PERMANENT AND CAN BE REVERSED IF THE ORGANIC MATTER BREAKS DOWN. (OWEVERo THERE WILL BE A PERMANENT CHANGE IN THE ACID STATUS OF THE SOIL IF THE TOPSOIL CONTAINING THE ORGANIC MATTER IS ERODED OR REMOVED. 4HE RELATIVE IMPORTANCE OF THESE CAUSES OF SOIL ACIDIlCATION FOR TWO FARMING SYSTEMS IS GIVEN IN 4ABLE 3. IS TO COMPARE THE SOIL TEST OF THE PADDOCK WITH A SIMILAR TEST OF A SAMPLE COLLECTED FROM AN AREA CLOSE TO THE PADDOCK THAT HAS NOT BEEN ROADSIDE. 0HOTO 5y 9ELLOW LEAF MARGINS OF CLOVER INDICATE AND 0A345RE 0ROD5C4)ON VARIES WITH SOIL P(. 3OME NUTRIENTS MAY REACH LEADING TO DElCIENCIES. 4HE INCREASED AVAILABILITY TOXICITY BEING A MAJOR PROBLEM FOR CROP AND PASTURE PRODUCTION IN ACID SOILS. OTHER PRODUCTION LOSSES MAY OCCUR WHERE ACIDITY REDUCES THE ACTIVITY OF BENElCIAL SOIL MICROh ORGANISMS. )T IS RECOGNISED THAT THE NITROGEN . ON LEGUME ROOTS IS RETARDED IN ACID SOILSo RESULTING IN LOWER NITROGEN AVAILABILITY AND REDUCED PRODUCTION. )N GENERAL THE CHANGES IN THE AVAILABILITY OF PLANT NUTRIENTS ASSOCIATED WITH INCREASING SOIL ACIDITY AREy )NCREASED AVAILABLE ALUMINIUM oAL STUNTED ROOT DEVELOPMENT IN CROPS AND PASTURES oSEE PHOTOS 1o 2o 3 AND 4s. 3TUNTED ROOTS RESULT IN REDUCED CAPABILITY TO ACCESS SOIL MOISTUREo AND REDUCED NUTRIENT UPTAKE. )NCREASED AVAILABLE MANGANESE o-N CAUSING REDUCED GROWTH IN SOME PLANTS IN IN SOLUTION IN A SOIL AT A GIVEN P( VARIES BETWEEN DIFFERENT SOIL TYPES. 7EAKLY WEATHERED SOILS THAT ARE ACIDIC TEND TO RELEASE TOXIC AMOUNTS ALUMINIUM. ALTERNATIVELYo HIGHLY WEATHERED SOILS oOTHER THAN A GROUP OF SOILS HIGH IN IRON AND ALUMINIUM OXIDESs TEND TO RELEASE LARGE AMOUNTS DIFFERENT SOILS RELEASE DIFFERENT AMOUNTS OF RECOMMEND A SINGLE P( AT WHICH LIMING SHOULD 4HE EFFECT OF ALUMINIUM oALs TOXICITY MOST OF THE PROBLEMS ASSOCIATED WITH ACIDIC SOILS. 4HE PRINCIPAL EFFECTS ON PLANT GROWTH FROM SOLUBLE ALUMINIUM IN THE SOIL SOLUTION AREy REDUCED ROOT MASS AND FUNCTION PRINCIPAL EFFECT OF ALUMINIUM TOXICITY IS TO REDUCE THE MASS AND FUNCTION OF ROOTS. CLUB SHAPED ROOTS. 4HIS REDUCES THEIR ABILITY TO EXTRACT MOISTURE FROM DEEP IN THE SOIL. o3EE 4YING UP PHOSPHORUS DElCIENCYo THAT ISo SMALL AND DARKhGREEN OR BECOME MORE PRONOUNCED AS THE ALUMINIUM LEVEL INCREASES. THAT APPLYING LIME TO STRONGLY ACIDIC SOILS SLIGHTLY INCREASES PLANT ACCESS TO SOIL PHOSPHORUS THAT IS NORMALLY OF LOW AVAILABILITY oSUCH AS RESIDUES OF PREVIOUSLY APPLIED FERTILISERs. 4HIS EFFECT IS USUALLY SMALLo AND NORMAL PHOSPHORUS APPLICATIONS ARE STILL REQUIRED WHEN LIME IS USED. . 6ERY HIGH LEVELS OF ALUMINIUM IN THE SOIL ALSO REDUCE THE UPTAKE AND SOILS WHERE THE P( REMOVE ALUMINIUM FROM THE SOIL SOLUTION. ALTERNATIVELY THE IMPACT OF ALUMINIUM CAN BE REDUCED BY GROWING PLANTS THAT CAN TOLERATE ALUMINIUM. DIFFERENT PLANTS SHOW DIFFERENT LEVELS 3EE 4ABLE 4. 4WO METHODS ARE COMMONLY USED TO MEASURE MEASURES THE ALUMINIUM IN THE 0.01- CACL EXTRACT USED TO DETERMINE P( WILL BE ENCOUNTERED BY THE PLANT ROOT. )T GIVES THE BEST PREDICTION OF THE EFFECT OF ALUMINIUM ON PLANT GROWTH. 4HE ALTERNATIVE METHOD MEASURES THE DETERMINATION OF THE EFFECTIVE CATION EXCHANGE GLOSSARYs. 4HE PROPORTION OF ALUMINIUM IN THE ECEC EXPRESSED AS A PERCENTAGE oAL REmECTS THE ALUMINIUM IN THE SOIL SOLUTION. 4HIS MEASUREMENT IS DETERMINED ROUTINELY BY COMMERCIAL LABORATORIES. 7HEN INTERPRETING THESE RESULTS THE ELECTRICAL CONDUCTIVITY oECs OF THE SOIL IS NEEDED TO ACCURATELY PREDICT THE EFFECT OF THE ALUMINIUM ON PLANT GROWTH. 4ABLE EXCHANGEABLE ALUMINIUM PERCENTAGE oAL FOR DIFFERENT ELECTRICAL CONDUCTIVITIES FOR THE MAJOR GROUPS OF PLANT TOLERANCE TO ALUMINIUM. A CRITICAL CONCENTRATION IS ONE THAT WILL REDUCE PLANT GROWTH BY 10l. NOTE WHEN THE ORGANIC MATTER IS OVER 5l IT MAY ADSORB SOLUBLE ALUMINIUM RESULTING IN SENSITIVE PLANTS BEING ABLE TO GROW IN SOILS WITH A LOW ROOTS AS THE SUBSURFACE SOIL CONTAINS LITTLE 4ABLE 4. ALUMINIUM SENSITIVITY oTOLERANCEs OF SOME CROP AND PASTURE PLANTS. (IGHLY SENSITIVE DURUM WHEATo MOST BARLEY CULTIVARSo FABA BEANSo LENTILSo CHICKPEASo LUCERNEo MEDICSo 3TRAWBERRYo "ERSEEM AND 0ERSIAN CLOVERSo "UFFEL GRASSo TALL WHEATGRASS 3ENSITIVE CUNNINGHAM m *ANZ WHEATo CANOLAo 9AMBLA BARLEYo ALBUS LUPINSo RED GRASS o7AGGAso WALLABY GRASS o D. LINKII so PHALARISo RED CLOVERo "ALANSA CLOVERo CAUCASIAN AND +ENYA WHITE CLOVERS. 4OLERANT 7HISTLERo 3UNSTATE m DIAMONDBIRD WHEATSo ANNUAL m PERENNIAL RYEhGRASSo TALL FESCUEo (AIFA WHITE AND SUBTERRANEAN CLOVERSo CHICORY. (IGHLY TOLERANT NARROW LEAF LUPINSo OATSo TRITICALEo CEREAL RYEo COCKSFOOTo KIKUYUo PASPALUMo YELLOW m SLENDER SERRADELLAo -AKU LOTUSo COMMON COUCHo CONSOL LOVE GRASS 4HESE ARE ONLY EXAMPLES. &OR THE CURRENT INFORMATION ON THE TOLERANCE OF CURRENT VARIETIES OF WINTER CROPS TO SOIL ACIDITY SEE THE PUBLISHED ANNUALLY BY N37 DEPARTMENT OF 0RIMARY )NDUSTRIES. 4ABLE 5. CRITICAL CONCENTRATIONS OF CALCIUM CHLORIDE EXTRACTABLE ALUMINIUM ALUMINIUM TOLERANCE OF PLANTS o4ABLE 4s CRITICAL LEVELS AL CA MGl, EQUIVALENT l AL EX FOR SOILS AT DIFFERENT ELECTRICAL CONDUCTIVITIES oEC 1y5 D3lMs ,OW EC  0.07 -ED. EC 0.07n0.23 HIGH EC  0.23 (IGHLY SENSITIVE 0.1n0.4 9n16 2n8 0.5n2 3ENSITIVE 0.5n0.8 17n20 9n12 3n6 4OLERANT 0.9n1.6 21n32 13n21 7n10 (IGHLY TOLERANT 1.7n2.7 33n43 22n30 11n16 ORGANIC MATTER AND IS THEREFORE HIGH IN SOLUBLE WILL INDICATE A REDUCTION IN THE AVAILABLE ALUMINIUM CAUSED BY ORGANIC MATTER TAKING THE 4HE EFFECT OF MANGANESE o-Ns TOXICITY 4OXICITY FROM EXCESSIVE AMOUNTS OF AVAILABLE MANGANESE CAN AFFECT THE GROWTH OF CROPSo PASTURE AND HORTICULTURAL CROPS IN SOILS WHERE AND THEN ONLY AT CERTAIN TIMES OF THE YEAR. 0LANTS REQUIRE MANGANESE IN SMALL AMOUNTS INCLUDING THOSE CONTROLLING THE PLANT HORMONES. 4OXIC AMOUNTS OF MANGANESE DISRUPT HORMONES. 4OXIC LEVELS OF MANGANESE DO NOT AFFECT THE PRODUCTIVITY OF CROPS AND PASTURES TO THE SAME EFFECTS ARE SOMETIMES COMPLICATED BY RELATED PROBLEMS. 4HE ANAEROBIC CONDITIONS ASSOCIATED TOXICITY BUTo OTHER PROBLEMS SUCH AS LOSS OF GASEOUS NITROGEN MAY RESULT IN MORE YIELD LOSSES MANGANESE CAN OCCUR IN N37o THE MAIN PROBLEM 0HOTO 6y 4HE EFFECT OF MANGANESE TOXICITY ON 4EAL WHEAT. &ROM LEFT TO RIGHT PLANTS WERE GROWN IN SOLUTIONS RANGING FROM 0o 90 TO 180 PPM 0HOTO 7y CANOLA LEAVES THAT ARE CUP SHAPED WITH YELLOW MARGINS INDICATING MANGANESE TOXICITY. IS TOXICITY. (OWEVERo EXCESSIVE APPLICATIONS OF LIME MAY RESULT IN MANGANESE DElCIENCY IN SOME LIGHT TEXTURED SOILS. SOME COMMON AGRICULTURAL PLANTS AREy 4HE EFFECT OF MANGANESE TOXICITY IS REDUCED VIGOUR WITH YELLOWING OF THE LEAF MARGINS oSEE PHOTO 7s. (IGHER LEVELS OF MANGANESE RESULT IN YELLOWING OF THE WHOLE LEAFo NECROSIS OF THE LEAF MARGINS AND GREATLY REDUCED VIGOUR OR DEATH. )N MOST SEASONS CANOLA GROWS DESPITE THE TOXIC EFFECTS OF DROPS IN LATE AUTUMN. ,UCERNEo MEDICSo SERRADELLA AND SUB CLOVER. 4HE EFFECT OF EXCESS MANGANESE IS REDUCED SEEDLING VIGOUR AND RED OR YELLOW LEAF MARGINS. NORMAL GROWTH RATES RETURN WITH A DECREASE IN AVAILABLE MANGANESE AS THE SEASON PROGRESSES. )F WARM TO HOT CONDITIONS RETURN AFTER THE lRST GERMINATION THE LEVEL OF AVAILABLE MANGANESE INCREASESo RENEWING THE EFFECT AND POSSIBLY CAUSING LEGUME PASTURE SPECIES GERMINATING IN THE AUTUMN CAN BE AFFECTED BY HIGH LEVELS OF AVAILABLE MANGANESE. ,UCERNE AND MOST MEDICS ARE HIGHLY SENSITIVEo WHILE SUB CLOVER AND SERRADELLA SEEDLINGS ARE ONLY AFFECTED BY ,ACK OF SEEDLING VIGOURo YELLOWING AT THE TIPS AND MARGINSo AND SOME mECKING OF THE OLDER LEAVES ARE INDICATORS OF MANGANESE TOXICITY oSEE PHOTO 6s. (OWEVERo OTHER NUTRITIONAL PROBLEMS CAN HAVE SIMILAR EFFECTS IN GRASSES AND TISSUE ANALYSIS IS REQUIRED TO CONlRM MANGANESE TOXICITY. TISSUE CAN HELP TO DETERMINE IF THERE IS A TOXIC MANGANESE PROBLEM. 3OME PLANTS ARE AFFECTED BY ONLY A SMALL AMOUNT OF MANGANESE IN THE TISSUEo WHILE OTHERS ARE 4ABLE 6. CRITICAL LEVELS OF MANGANESE FOR VARIOUS PLANTS. -ANGANESE TOLERANCE CATEGORY 0LANT CRITICAL LEAF MANGANESE LEVEL oMGlKGs (IGHLY SENSITIVE ,UCERNEo PIGEON PEAo BARREL AND BURR MEDICS 200n400 3ENSITIVE 7HITE CLOVERo STRAWBERRY CLOVERo CHICKPEAo CANOLA 400n700 4OLERANT 3UB CLOVERo COTTONo COWPEAo SOYBEANo WHEATo BARLEYo TRITICALEo OATS 700n1000 (IGHLY TOLERANT RICEo SUGAR CANEo TOBACCOo SUNFLOWERo MOST PASTURE GRASSESo OATSo TRITICALEo 4IGAo CURRENCYo CEREAL RYE  1000 3EE N37 D0) 7INTER CROP VARIETY SOWING GUIDE FOR MORE INFORMATION &IGURE 5. 6ARIATION OF MANGANESE AVAILABILITY WITH SEASON. IN GROWTH WILL OCCUR CAN VARY FROM 200 TO OVER 1000 MGlKG OF PLANT DRY MATTERo DEPENDING ON GROWTH FOR A NUMBER OF SPECIES ARE GIVEN IN 4ABLE 6. 4HESE LEVELS ARE DETERMINED ON THE 3OME PLANTS ARE MORE SENSITIVE TO ALUMINIUM FOURhFOLD THROUGH THE YEAR AS SHOWN IN &IGURE 5. CHANGES FROM AN UNAVAILABLE FORM oOXIDISEDs TO AN AVAILABLE FORM oREDUCEDs. 4HIS EFFECT IS LESS IN A WET SUMMER. 7ATERLOGGED CONDITIONS IN SPRING CAN PRODUCE HIGH LEVELS OF AVAILABLE MANGANESE. (OWEVERo LOW LEVELS OF OXYGEN AND LOSS OF NITROGEN ASSOCIATED WITH WATERLOGGING ARE LIKELY TO AFFECT THE PLANTS MORE THAN THE HIGH MANGANESE LEVELS. RAIN IN AUTUMN CREATES A SOIL ENVIRONMENT THAT FAVOURS MICROmORA WHICH CONVERT THE MANGANESE BACK TO AN UNAVAILABLE oOXIDISEDs FORM. )T LOWEST IN WINTERo ALTHOUGH POTENTIALLY TOXIC LEVELS MAY REMAIN IF THE CONDITIONS ARE TOO COLD IN AUTUMN oSOIL TEMPERATURES LESS THAN 10ªCs FOR THE MICROmORA TO CHANGE THE AVAILABLE MANGANESE TO THE UNAVAILABLE FORM. CAN VARY UP TO FOURhFOLD THROUGH THE YEAR IN RESPONSE TO TEMPERATURE AND RAINFALLo A SOIL TEST WHICH MEASURES AVAILABLE MANGANESE AT ONE TIME IN THE YEAR CANNOT BE RELIED ON TO DETERMINE IF MANGANESE TOXICITY IS LIKELY TO BE A PROBLEM AT ANOTHER TIME. &OR EXAMPLEo IT IS NOT POSSIBLE TO PREDICT THE LEVEL OF AVAILABLE LUCERNEo FROM A SOIL SAMPLE TAKEN IN &EBRUARY.