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English: The quantitative evaluation of crop production potential is important for sustainable and wise land use as well as for food security where subsistence farmers are involved. It is of particular importance in arid and semi-arid areas where rainfall is marginal and variable. This study aims at making a quantitative evaluation of the maize production potential of the Glen/Hutton and Glen/Oakleaf ecotopes which are located at the Glen Agricultural Research Station in the semi-arid Free State Province of South Africa. The objective was to characterize the ecotopes, and to make long-term yield predictions with a yield prediction model using long-term climate data. A detailed profile description, soil analyses and an in situ drainage curve were made for the Glen/Oakleaf ecotope. Similar data for the Glen/Hutton ecotope was obtained from previous research work (Hensley et al., 1993; Hattingh, 1993; Hensley, personal communication, 2002). A neutron water meter (NWM) was calibrated for each horizon of the Oakleaf soil on the Glen/Oakleaf ecootpe. The plant available water (PAW), defined as the differences between the drained upper limit (DUL) and the lower limit (LL), for maize grown on the Glen/Hutton and Glen/Oakleaf ecotopes was 133 mm and 120 mm respectively. Considering a mature maize crop growing in summer on these two ecotopes, PAW can be defined as the difference between the crop modified upper limit (CMUL) and LL. Results for this parameter were 183 mm and 192 mm for the Glen/Hutton and Glen/Oakleaf ecotopes respectively. The reason for the relatively high value of the latter is its slower drainage rate, which enables the crop to extract more water while drainage proceeds between field saturation and DUL than in the rapidly draining Hutton soil. Yields measured on experiments on the two ecotopes for 12 seasons on the Glen/Hutton and 10 seasons on the Glen/Oakleaf ecotope indicate that these two ecotopes have similar production potentials. For the development, Afrikaans: Kwantitiewe evaluering van gewasproduksie potensiaal is belangrik vir volhoubare grondgebruik en voedselsekuriteit waar kleinboere betrokke is. Dit is veral belangrik in ariede en semi-ariede gebiede waar reënval marginaal en wisselvallig is. Die doel van hierdie studie was om so 'n evaluering te maak vir mielies op die Glen/Hutton en Glen/OakleaJ ekotope geleë op die Glen Landbounavorsingstasie in 'n semi-anede gebied in die Vrystaat Provinsie van Suid-Afrika. Die doel was om die ekotope te karakteriseer, en om lengtermyn oesopbrengs voorspellings te maak met behulp van 'n opbrengsmodel saam met langtermyn klimaatdata. 'n Gedetaileerde profielbeskrywing, grondontledings en veldbepaalde dreineringskurwe is gemaak vir die Glen/OakleaJ ekotoop. Vergelykbare inligting vir die Glen/Hutton ekotoop is verkry van vroeër navorsingswerk (Hensley et al,. 1993; Hattingh, 1993; Hensley, personal communication, 2002). 'n Neutron watermeter (NWM) is gekalibreer vir elke horison van die wortelsone van die Oakleaf grond. Die veldbepaalde plantbeskikbare water (pA JJ? vir mielies, gedefineer as die verskil tussen die gedreineerde boonste grens (DUL) en die onderste grense (IL), was 133 mm op die Glen/Hutton ekotoop en 120 mm op die Glen/OakleaJ ekotoop. Met 'n volwasse gewas op hierdie ekotope in die somer kan PAW gedefineer word as die verskil tussen 'n gewasaangepaste boonste grens (CMUL) en LL. Resultate vir hierdie parameter vir mielies op die Glen/Hutton ekotoop is 183 mm, en vir die Glen/OakleaJ ekotoop 192 mm. Die rede vir die relatiewe hoë waarde van laasgenoemde is die baie stadiger tempo van dreinering wat dan toelaat dat die mielies meer water bokant DUL kan ekstraheer terwyl dreinering nog plaasvind. Opbrengste gekry met veldproewe op die twee ekotope vir 12 seisoene op die GlenlHutton en 10 seisoene op die Glen/OakleaJ ekotoop dui daarop dat die produksiepotentiaal vir mielies op die twee ekotope min of meer dieselfde is. Vir die ontwikkeling van 'n opbrengsm, World Bank, EHRD

English: The Weatherley catchment is situated close to Maclear in the northern Eastern Cape Province. Soil water contents have been measured regularly, as part of a long-term project, at 28 sites in the catchment for six years to quantify the soil water regime. For this study tEm of these sites were selected, described and analysed in detail to characterize the soil properties. This data was used to determine the relationship between soil water regime and soil profile morphology. A correlation was found to exist between mean annual duration of water saturation above 0.7 of porosity (ADs>o.7, days year") and other soil properties. CECsoil increases from 3.5 to 11.5 crnol, kg-1 , base saturation increases from 25 to 44 %, and the underlying unspecified material with signs of wetness or G horizons occur closer to the soil's surface as mean ADs>o.7 increases. Orthic A horizons that occur in seeps are wetter, with mean ADs>o.7 212 - 365 days year", than orthic A horizons that occur on ridges with mean ADs>o.7 of < 25 days year". The former have common and many Fe oxide mottles, whereas the latter lack clear mottling. ADs>o.7 data.shows that orthic A horizons overlying red apedal B, yellow-brown apedal B or neocutanic B horizons are well drained, while those overlying E, soft plinthic Band G horizons are wetter. It is proposed that orthic A horizons can be subdivided into wetness classes using the occurrence of mottles, as well as the nature of the underlying horizon. The Longlands (P201 and P207) and Westleigh (P204) soils, characterized by the occurrence of a soft plinthic B horizon, have intermediate mean ADs>o.7. They increase from 84 to 157 days year" in orthic A horizons, to 231 days year" in soft plinthic B horizons and 360 days year" in the underlying unspecified material with signs of wetness. The chromatic soils, including Pinedene (P202), Tukulu (P203) and Bloemdal (P210) soil forms, defined as having yellow-brown apedal B, neocutanic B or red apedal B horizons, Afrikaans: Die Weatherley opvanggebied is naby Maclear in die Noordelike Oos-Kaapprovinsie geleë. As deel van 'n langtermyn projek is grondwaterinhoud gereeld vir ses jaar by 28 lokaliteite in die opvangebied gemeet om die grondwaterregime te kwantifiseer. Vir hierdie studie is tien van hierdie lokaliteite is geselekteer, in detail beskryf en geanaliseer om die grondeienskappe te karakteriseer. Hierdie data is gebruik om die verwantskap tussen grondwaterregime en grondmorfologie te bepaal. 'n Korrelasie is tussen jaarlikse duur van waterversadiging bo 0.7 van porositeit (ADs>o.7, dae [aar") en ander grondeienskappe gevind. KUKgrondneem toe van 3.4 na 11.5 crnol, kg-1 , basis versadiging neem toe van 25 % na 44 %, en die onderliggende ongespesifiseerde materiaal met tekens van natheid of G horisonte kom nader aan die grondoppervlak voor, soos ADs>o.7 toeneem. Ortiese A horisonte wat in vleie voorkom is natter (gemiddelde ADs>o.7 212 - 365 dae [aar'") as ortiese A horisonte wat op kruine (gemiddelde ADs>o.7 < 25 dae [aar'") voorkom. Eersgenoemde het volop en baie Fe oksied vlekke, terwyl laasgenoemde geen duidelike vlekke het nie. ADs>o.7 data dui daarop dat ortiese A horisonte watbo rooi apedale B, geelbruin apedale B of neokutaniese B horisonte voorkom goed gedreineer is, terwyl ortiese A horisonte wat op E, sagte plintiese B en G horisonte voorkom relatief nat is. Daar word voorgestel dat ortiese A horisonte in natheidsklasse onderverdeel kan word deur die voorkoms van vlekke en die aard van die onderliggende materiaal te gebruik. Die Longlands (P201 en P204) en Westleigh (P207) gronde, gekarakteriseer deur die voorkoms van sagte plintiese B horisonte, het intermediêre gemiddelde ADs>o.7. Dit neem toe van 84 tot 157 dae [aar" in ortiese A horisonte, na 231 dae [aar" in sagte plintiese B horisonte en 360 dae [aar" in die onderliggende ongespesifiseerde materiaal met tekens van natheid. Chromatiese gronde, wat die Pindene (P202), Tukulu (P203) en Bloemdal (P210) insl

English: Understanding the process of organic matter degradation and restoration is important with regard to sustainable agricultural production on any agro-ecosystem, and of particular importance where degradation is relatively rapid, such as in the coarse textured savannah soils of the South African highveld. Organic matter degradation studies on such soils in three agro-ecosystems, Harrismith, Tweespruit and Kroonstad, have been undertaken by Du Toit et al. (1994), and Lobe et al. (2001). This study is concerned with organic matter restoration on the same agro-ecosystems, and is therefore complementary to the two earlier studies. The objective was to investigate organic matter restoration at three depths, 0-50, 50-100 and 100- 200 mm, on perennial pastures of different ages that had been established on lands which had been cultivated continuously for more than 20 years. Representative C and N values for degraded lands and virgin grasslands for the three agro-ecosystems were obtained from the studies of Du Toit et al. (1994) and Lobe et al. (2001), and used as reference values. To reduce within-site error samples were collected at six places, separated from each other by a few meters, at each site. At each of these places six subsamples of each layer were taken to make up the final sample. There were therefore 18 soil samples per site. A total of 28 sites, ranging in ages from 4 to 25 years, were identified and sampled on the three agro-ecosystems, All the samples were analyzed for C and N, and selected samples were analyzed to characterize the soil fertility levels and particle size distribution at each site. Results showed a wide variation in the rate of organic matter restoration between sites in each of the agro-eco systems , due mainly to differences in natural resource factors and management techniques. Most important of the latter was the application of N fertilizer. Where this was inadequate or absent, very low organic matter restoration rates were general, Afrikaans: Met betrekking tot volhoubare landbouproduksie is dit belangrik om die degradasie en restorasie prosesse van organiese materiaal op enige landbou-ekosisteem te verstaan. Waar degradasie relatief vinnig is, soos op die grof getekstuurde gronde van die Suid-Afrikaanse hoëveld, is dit van spesiale belang. Du Toit et al. (1994) en Lobe et al. (2001) het organiese materiaal degradasie op sulke gronde ondersoek in die drie landbou-ekosisteme Harrismith, Tweespruit en Kroonstad. Die studie wat hier beskryf word fokus op die restorasie van organiese materiaalop dieselfde landbou-ekosisteme, en dien dus as ondersteuning vir die twee vorige studies. Die doel was om organiese materiaal restorasie op drie dieptes, 0-50, 50-100 en 100-200 mm, te ondersoek op meerjarige weidings van verskillende ouderdomme wat gevestig is op lande wat voorheen vir meer as 20 jaar onder bewerking was. Verwysingswaardes van C en N vir gedegradeerde lande en onversteurde grasveld op die drie landbou-ekosisteme is verkry uit die data van Du Toit et al. (1994) en Lobe et al. (2001). Ses monsterplekke is gebruik om die ruimtelike variasie by elke meetpunt te minirniseer. Die monsterplekke was 'n paar meter van mekaar geleë. Ses submonsters is by elke monsterplek geneem volgens 'n standaard prosedure, en dan gemeng om die finale monster op te maak. Daar was dus 18 finale grondmonsters per meetpunt. Die totale getal meetpunte op die drie landbou-ekosisteme was 28, met weidings tussen 4 en 25 jaar oud. Al die monsters is ontleed vir C en N, en geselekteerde monsters is ontleed om die grondvrugbaarheid en deeltjiegrootteverspreiding by elke meetpunt te karakteriseer. Resultate wys 'n groot variasie in die tempo van organiese materiaal restorasie op die drie landbou-ekosisteme, hoofsaaklik weens verskille in natuurlike hulpbron faktore en bestuurspraktyke. Vanlaasgenoemde is die toediening van stikstofkunsmis die belangrikste. Waar dit te min was het metings 'n baie lae tempo van organiese materi