Digitaria eriantha fertilised with limestone ammonium nitrate (LAN 28 % N), although not statistically significant, resulted in higher dry matter production in comparison to those plants fertilised with urea (U 46% N). Significant lower (P\u3c0.05) soil calcium levels were found in plots fertilised with LAN. Plants fertilised with urea had double the amount of Aspartic and Glutamic acid, indicating that urea did not convert to NO3 -, but was taken up as ammonium

Kruger, G.H J

Reckling, J F

English

University of Kentucky

Session 10 - Soil Fertility 10-13Calcium.  A statistically significant decline in soil calcium was foundas illustrated in Figure 1.Dry matter production.  In agreement with Rethman (1987) nosignificant difference in dry matter production was found on plotsfertilised with LAN or urea.  However, plots fertilised with LANrecorded higher dry matter production, consistently over the threeyear period.Amino acids.  The amino acid concentration of Digitaria erianthaabove ground dry matter samples are illustrated in Table 1.DISCUSSIONWhen NH4+ and NO3- are supplied in equal concentrations to ryegrass(Clarkson & Warner 1979), NH4+ was absorbed more readily thanNO3- at lower temperatures.  Due to the relatively high temperaturesexperienced at Potchefstroom the absorption of NO3- will thereforebe enhanced.  The tendency of Digitaria eriantha, fertilised withLAN, to produce more abundantly may be attributed to the fact thatNO3- is readily available. If NH4+ and NO3- are supplied in unequalconcentrations plants absorb the nitrogen source which occurs less(Jones, 1985).  This implies that LAN is duly benefited because NO3-and NH4- are supplied in equal amounts while urea is converted toNH4+ and then to NO3-.  According to Mengel & Kirby (1987) ureafertilisation on sunflowers resulted in lower absorption of nitrogenand disturbance of protein metabolism and a pronouncedaccumulation of aspargine occurred.  In the amino acid analysis,plots fertilised with 90 kg N ha-1 urea had double the amount ofglutamine, aspartic acid and proline in comparison to plots fertilisedwith  90 kg  N ha-1 LAN.  The higher concentration of glutamaticacid therefore indicates that NH4+ was readily taken up by Digitariaeriantha before oxidisation could take place.  In agreement with Miles& Manson (1992) the significant (P<0.05) decline in Ca2+ in all LANplots can be attributed to leaching of NO3- or after nitrification ofunused NH4+ fertiliser and nutrient export. Together with double theamount of glutamine acid present in Digitaria eriantha samples,fertilised with urea, indicates that urea did not convert to NO3-.CONCLUSIONUrea is volatile and therefore the lower yields obtained with ureafertilisation may be due to volatilisation, resulting in less availablenitrogen for growth.  Furthermore it would thus seem that theconversion of urea to nitrate is not always efficient.  The influenceof external factors must therefore be quantified, to enable researchersto address this lower efficiency of urea.REFERENCESBarnard, R. O., Buys, A. J., Coetsee, J. G. K., Du Preez, C. C.,Meyer, J. H., Van Der Merwe, A. J., Van Vuuren, J. A. J. &Volschenk, J. E. 1990.  The non-affiliated soil analysis workcommittee.  Handbook of standard soil testing methods for advisorypurposes.  Soil Sci. Soc. of S.A., P. O. Box 30030, Sunnyside,Pretoria.Clarkson, D. T. & Warner, A. J. 1979.  Relationship between roottemperature and the transport of ammonium and nitrate ions by Italianand perennial ryegrass (Lolium multiflorum and Lolium perenne).Plant Physiol. 64: 557-561.ABSTRACTDigitaria eriantha fertilised with limestone ammonium nitrate (LAN28 % N), although not statistically significant, resulted in higher drymatter production in comparison to those plants fertilised with urea(U 46% N).  Significant lower (P<0.05) soil calcium levels werefound in plots fertilised with LAN.  Plants fertilised with urea haddouble the amount of Aspartic and Glutamic acid, indicating thaturea did not convert to NO3-, but was taken up as ammonium.INTRODUCTIONThe response regarding dry matter production of Digitaria erianthato nitrate nitrogen fertilisation proved to be better than its responseto ammonium nitrogen (Wolfson & Creswell, 1984).  Evaluating theinfluence of four commercially available nitrogenous fertilisers onthe dry matter production of Digitaria eriantha, at Nooitgedacht ina moderate climatic zone, Rethman (1987), however, showed thatdry matter yields obtained with urea (U 46% N), though notsignificantly lower, tended to record lower yields compared to LANand ammonium sulphate (AS 21% N) fertilisation.  No dataconcerning the difference in yields, as influenced by LAN and urea,in the semi-arid region of South Africa, is available.  The objectiveof this study was: (i) to determine whether commercially availablenitrogenous fertilisers differed in their effectiveness in a semi-aridenvironment; (ii) investigate changes in soil properties due tofertilisation and mechanical defoliation and (iii) whether differentnitrogenous fertilisers influence plant chemical analyses.Procedure. The trial was conducted at the North West AgriculturalDevelopment Institute at Potchefstroom.  The precipitation recordedduring the effective growing period was 823 mm in 1993/94, 346mm in 1994/95 and 1100 mm during the 1995/1996 season.  TheDigitaria eriantha pasture was established in 1985 on a sandy clayWestleigh soil (Macvicar et al., 1977) with an effective depth of 500mm.Treatments and trial layout.   The investigation conducted as a 2 x4 x 4 simple factorial design. Treatments consisted of two nitrogenousfertilisers, LAN 28 % N and urea (U 46% N).  Each was applied atfour different levels of 0, 30, 60 and 90 kg N ha-1.  A single applicationwas applied in October before the growing season.  The sametreatment was applied each year to the same locality.  Aftercompletion of the trial representative soil analyses were carried outfor each treatment (Barnard et al 1990).  After field determination ofplant yield, representative samples were dried at 70½C to a constantmass for determination of dry matter content and thereafter allsamples were chemically analysed for amino acids as described byKenneth et al. (1977).Statistical analysis.  All data was subjected to comparison by meansof the Bonferroni paired t-test (SAS, 1985).  The significance ofcorrelations were detected by analysis of variance.RESULTS AND DISCUSSIONDue to nitrogen fertilisation a decline in soil pH, P, K and Mg wasfound, over the three year period.  No statistical significant differenceswere found between nitrogen sources or treatments.ID NO. 346EVALUATION OF DIFFERENT NITROGEN SOURCES ON THE PRODUCTION ANDCHEMICAL PROPERTIES OF C4-SUB-TROPIC PASTURES.I.F. Reckling*, G.H.J. Krüger* NWADI, Private Bag X804, Potchefstroom, 2520, Republic of South AfricaSession 10 - Soil Fertility 10-14Jones, G. A. 1985.  C4 grasses and cereals.  Growth, developmentand stress responses. Wiley Int. Pub. New York. pg: 190-331.Kenneth, R. L., Rice,  H. R. & Gehrke, C. W. 1977.  Completemass spectra of N-trifluoroacetyl-n-butyl esters of amino acids.J.Chromatography. 141: 123-144.Macvicar, C.N., De Viliers, J.M., Loxton, R.F., Verster,E.,Lambrechts, J.J.N., Merryweather, F.R., Le Roux, J., VanRooyen, T.H. & Harmse, H.J. Von M. 1977.   Soil classification.A binomial system for South Africa. Department of AgriculturalTechnical Services, Pretoria.Mengel, K. & Kirby, E. A. 1987.  Principles of plant nutrition.  Pub.International Potash Inst.  Bern, Switzerland. :427-488.Miles, N. & Manson, A. D. 1992. Considerations on thesustainability and environmental impact of intensive pastures. J.Grassl. Soc. Sth. Afr. 9: 135-140.Rethman, N. F. G. 1987.   The effect of form and level of nitrogenfertilization on the yield of Digitaria eriantha Steud. J. Grassl. Soc.South Afr. 4, (3): 105-108.SAS, 1985.  Statistical Analysis Systems Users Guide (5th edn.).Institute Inc. Raleigh, North Carolina.Wolfson, Maureen, M. & Cresswell, C.F.   1984.  The effect ofnitrogen on the development and photosynthetic activity of Digitariaeriantha  Steud. subsp. eriantha.  J. Grassl. Soc. Sth. Afr.,1: 33-36.Table 1Amino acid concentration (µg 100 mg-1, dryweight), obtained undernatural conditions and fertilised with 0 and 90 kg N ha-1 of the sourceLAN and urea, after completion of trial (1993-1996) atPotchefstroom.0 kg  N/ha 90 kg N/ha 90 kg N/haUrea LANCrude protein 11.5 14 14Threonine 38.6 6.427 44.22Valine 20.9Methionine 4.882 12.53 5.23Isoleucine 13.33Leucine 28.67 75.67Phenyl-alanine 17.71 - 16.46Glycine 6.332 3.118Glutamic 43.35 88.25 48.49Aspartic 12.95 54.94 20.42Alanine 7.43 39.8 21.14Proline 57.48 140.48 69.52Figure 1The influence of LAN and urea fertilisation as well as defoliation on residual soil calcium levels at Potchefstroom, over a three year period(1993-1996), on a sandy clay Westleigh soil.

Evaluation of Different Nitrogen Sources on the Production and Chemical Properties of C4-Sub-Tropic Pastures

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Evaluation of Different Nitrogen Sources on the Production and Chemical Properties of C4-Sub-Tropic Pastures

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