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Labels: endangered species, Javan rhino, Vietnamese wild life Retention and release of applied phosphorus by the benchmark soils of Lesotho
Molete, Sebolelo Francina
English: A lack of information on the behaviour of applied phosphorus (P) in and on the P requirements of the benchmark soils of Lesotho precludes the establishment of proper application recommendations of P fertilizer for crop production. Therefore, the objectives of this thesis were to determine the P retention capacities and P requirement factors of these soils and identify soil properties implicated therein. Eleven benchmark soil senes, each replicated at least five times were sampled in the lowlands and foothills for P retention studies. These soil samples were prepared as usual for laboratory analyses and characterized especially for the soil properties implicated in P retention. The soil series varied with regard to those properties, providing a good indication of their variability in Pretention. A pilot experiment was conducted on some of the soils to investigate an optimum incubation period for P retention and release studies. The soils were incubated with P levels equivalent to 0, 50, 100, 200 and 400 kg P ha-1, respectively at 85% water filled porosity, which was checked fortnightly. The experiment was laid out in a randomized complete block design at room temperature. Phosphorus retention was then determined 7, 14, 21, 28, 42 and 63 days after P application using the Olsen extraction procedure. The results of this experiment indicated an incubation period of 42 days as practically suitable for Pretention and release studies on the benchmark soils. Thereafter a P retention experiment with Il soil series, five P levels and five soil phases, all replicated three times, was conducted. The soils were incubated with the same levels of P as in the pilot experiment, for 42 days at 85% water filled porosity that was again checked fortnightly. The experiment was set-up in a split-split plot design, at room temperature. After 42 days P was extracted with Bray and Olsen extractants, respectively and retained P was calculated as the difference between applied and extracted P. Percentage of applied P retained against the Bray and Olsen extract ants varied from 6 to 97 and 21 to 91, respectively. The slopes of retained P against applied P, viz. P retention indices (PRI's) varied from -0.04 to 0.28 for Bray and 0.07 and 0.27 for Olsen while the respective slopes of retained P against extracted P, viz. P buffering indices (PBI's) varied from 2 to 55 and 12 to 103. The PRI's and PBI's were closely correlated, r = 0.94 and 0.81 (P < 0.0001) for Bray and Olsen, respectively. The series Fusi, Thabana, Machache and Sefikeng had higher PRI's and similarly higher PBI's than the rest of the series, viz. Khabos, Leribe, Rama, Sephula, Tumo, Matela and Berea, particularly according to the Bray method. In the case of the Olsen method however, the series Khabos and Tumo had comparable PBI's with the series Fusi, Thabana, Machache and Sefikeng though their PRI's were significantly lower. The series Fusi, Thabana, Machache and Sefikeng also had the highest P retention capacity at an application of 400 kg P ha-1 (PRC at P400) of about 69 to 83% for Bray and 75 to 81% for Olsen. The respective PRC at P400 for the rest of the series were 0 to 39 and 47 to 66%. For all the soils the slopes of applied P against extracted P, viz. P requirement factors (PRF's) ranged from 0.85 to 1,1.40 (Bray) and 1.45 to 9.07 (Olsen). The high Pretaining series (Fusi, Thabana, Machache and Sefikeng) had high mean PRF's of 3.36 to 7.13 for Bray and 3.85 to 5.47 for Olsen. For both the Bray and Olsen procedures the parameters PRI, PRC at P400, PBI and PRF were with a few exceptions highly correlated (r2> 0.60) with sample density, sand, clay, organic carbon, cation exchange capacity, acid ammonium oxalate and citrate bicarbonate dithionite extractable iron and aluminium. Multiple linear regression models were also obtained for each of the parameters with some of the soil properties. Recommendations were made with regard to reducing P retention and increasing P availability in the high P sorbing soils and hence to improve crop production.
Afrikaans: 'n Gebrek aan inligting oor die gedrag van toegediende fosfor (P) in en oor die P behoeftes van die verwysingsgronde van Lesotho kortwiek die instelling van behoorlike toedieningsaanbevelings van P kunsmis vir gewasproduksie. Daarom was die oogmerke van hierdie proefskrif om die P retensiekapasiteite en P behoeftefaktore van die gronde vas te stel en grondeienskappe betrokke daarby te identifiseer. Elf verwysingsgrondseries wat elk ten minste vyf keer herhaal is, is in die laaglande en voetheuwels vir P retensie studies gemonster. Hierdie grondmonsters is soos gebruiklik vir laboratoriumontledings voorberei en gekarakteriseer veral vir daardie eienskappe wat 'n rol speel by P retensie. Die grondseries het gevarieer met betrekking tot daardie eienskappe wat 'n goeie aanduiding is van hulle varieerbaarheid in Pretensie. 'n Loodseksperiment is op sommige van die gronde gedoen om 'n optimum inkubasieperiode vir P retensie en vrystelling te ondersoek. Die gronde is geïnkubeer met P vlakke ekwivalent aan onderskeidelik 0, 50, 100, 200 en 400 kg P ha-1 by 'n 85% watergevulde porositeit wat tweeweekliks gekontroleer is. Fosforretensie is 7, 14, 21, 28, 42 en 63 dae na P toediening bepaal deur die Olsen ekstraheringsprosedure te gebruik. Die resultate van hierdie eksperiment het daarop gedui dat 'n inkubasieperiode van 42 dae prakties geskik is vir studies van P retensie en vrystelling op die verwysingsgronde. Daarna is 'n P retensie eksperiment gedoen met 11 grondseries, vyf P vlakke en vyf grondfases wat alles drie keer herhaal is. Die gronde is geïnkubeer met dieselfde P vlakke soos in die loodseksperiment vir 42 dae by 85% watergevulde porositeit wat weereens tweeweekliks gekontroleer is. Die eksperiment is as 'n verdeelde-verdeelde perseelontwerp by kamertemperatuur uitgevoer. Na 42 dae is P geëkstraheer met onderskeidelik Bray en Olsen ekstraheermiddels en vasgelegde P is bereken as die verskil tussen toegediende en geëkstraheerde P. Persentasie van toegediende P wat nie geëkstraheer is met Bray en Olsen ekstraheermiddels nie varieer van 6 tot 97 en 21 tot 91, respektiewelik. Die hellings van vasgelegde P teen toegediende P, te wete Pretensie-indekse (PRI'e) het gevarieer van -0.04 tot 0.28 vir Bray en van 0.07 tot 0.28 vir Olsen, terwyl die onderskeie hellings van vasgelegde P teen geëkstraheerde P, te wete P bufferindekse (PBI'e) gevariëer het van 2 tot 55 en 12 tot 103. Die PRI'e en PBI'e het goed gekorreleer, r = 0.94 en 0.81 (P < 0.0001) vir Bray en Olsen respektiewelik. Die series Fusi, Thabana, Machache en Sefikeng het hoër PRI' e en dienooreenkomstig hoër PBI' e as die res van die series, te wete Khabos, Leribe, Rama, Sephula, Tumo, Matela en Berea, veral volgens die Bray metode. In die geval van die Olsen metode het die series Khabos en Tumo egter soortgelyke PBI'e as die series Fusi, Thabana, Machache en Sefikeng hoewel hulle PBI'e betekenisvollaer is. Die series Fusi, Thabana, Machache en Sefikeng het ook die hoogste P retensiekapasiteit by 'n toediening van 400 kg P ha-l (PRK by P400) van 69 tot 83% vir Bray en 75 tot 81% vir Olsen. Die onderskeie PRK by P400 vir die res van die series was 0 tot 39 en 47 tot 66%. Vir al die gronde het die hellings van toegediende P teen geëkstraheerde P, te wete die P behoeftefaktore (PBF'e) gevariëer van 0.85 tot 11.40 (Bray) en 1.45 tot 9.07 (Olsen). Die hoë P retensie series (Fusi,Thabana, Machache en Sefikeng) het hoë gemiddelde PBF'e van 3.36 tot 7.13 vir Bray en 3.85 tot 5.47 vir Olsen. Vir beide die Bray en Olsen ekstraksie prosedures het PRI, PRK by P400, PBI en PBF met enkele uitsonderings hoogs gekorreleer (r > 0.60) met monsterdigtheid, sand, klei, organiese koolstof, katioonuitruilkapasiteit en suur ammonium oksalaat en sitraat bikarbonaat ditioniet ekstraheerbare yster en alumunium. Meervoudige lineêre regressiemodelle is ook verkry vir elk van die parameters met sekere van die grondeienskappe wat 'n rol speel by Pretensie. Aanbevelings word gemaak met betrekking tot die vermindering van P retensie en vermeerdering van P toeganklikheid in die hoë P sorberende gronde ten einde gewasproduksie te verbeter.