Site and land use effects on some physical properties and the distribution of total carbon, aluminium, and iron within aggregates of some humic soils in KwaZulu-Natal, South Africa.

Abstract

Humic soils occur mainly on old land surfaces, with a warm, misty climate having native forests and grasslands as the predominant natural vegetation, in KwaZulu-Natal and along the coast of Pondoland and the eastern escarpment of Mpumalanga. The effects of site characteristics and response to replacement of native vegetation with sugarcane cultivation on these soils, remain unclear. This study investigated the effects of different site conditions, including native forest, grassland, and sugarcane production, on (i) general soil characteristics such as pH, clay mineralogy, and total Al, Fe, and C in bulk soils, (ii) bulk density (BD), total porosity (TP), saturated hydraulic conductivity (Ks), and moisture content at field capacity (FC) and permanent wilting point (PWP), (iii) AS and size distribution, and (iv) the distribution of total Al, Fe, and C within different aggregates in humic soils. The study area encompasses different soil types developed on dolerite and sandstone, under various vegetation covers, and subjected to different land uses. Soil samples were collected at different depths to compare forest vs. grassland sites and forest vs. sugarcane sites. Results revealed differences in pH, organic carbon content (TOC), Al, Fe, clay, and silt content among sites, with sugarcane cultivation notably affecting BD and Ks. Interestingly, while TOC influences water retention characteristics to some extent, factors like texture, especially silt, play a more significant role. Soils with higher TOC exhibited better aggregation, resulting in lower BD and higher TP, thereby enhancing Ks, FC, and PWP. Exchangeable acidity and silt were identified as critical factors in aggregation, with Al and Fe concentrations increasing with sugarcane cultivation across all aggregates. The study emphasizes the importance of soil management practices to ensure sustainable agricultural production on these soils. Recommendations include lime application to reduce soil acidity and improve exchangeable base availability. Practices such as adding organic matter, minimizing tillage, and crop rotation are suggested to maintain or enhance TOC content, thereby promoting stable aggregates and preventing soil degradation. Generally, the findings highlight the complex interplay between land use, soil properties, and management practices in shaping the sustainability of agricultural systems on humic soils in South Africa.

Iqoqa.

Inhlabathi enomquba wamahlamvu omileyo etholakala ikakhulukazi ezindaweni ezindala, ezinesimo sezulu esishisayo, esinenkungu enamahlathi emvelo kanye nezithako ezinotshani, njengezitshalo zemvelo ezihamba phambili, KwaZulu-Natal nasogwini lwaseMampondweni kanye nendawo esempumalanga yeMpumalanga. Imiphumela yezimpawu zesizinda kanye nokusabela ekushintsheni kwezimila zomdabu kutshalwa umoba kule nhlabathi, ayikacaci. Lolu cwaningo luphenye imiphumela yezimo ezahlukene zezindawo, okuhlanganisa ihlathi lendabuko, imfunda yotshani, nokukhiqizwa komoba, (i) izimpawubunjalo ezijwayelekile zomhlabathi njenge-pH, ezamamineral asemhlabathini, kanye nengqikithi ye-Al, Fe, no-C emhlabathini omningi, (ii) kanye nesisindo esikhulu, ibulk density (BD), enobuzikamanzi obuphelele, itotal porosity (TP), izindlela zokuhambisa amanzi emhlabathini (Ks), nokuqukathwa komswakamo emasimini (FC) kanye nenani lamanzi elidingakalyo emhlabathini, ipermanent wilting point (PWP), (iii) i-AS nobungako bamaphesenti adingakalayo, kanye (iv) nokusabalalisa ingqikithi ye-Al, Fe, kanye no-C phakathi kwenhlanganisela ehlukene enhlabathini evundile. Indawo yocwaningo ihlanganisa izinhlobo zenhlabathi ezehlukene ezakhiwe ohlotsheni lwetshe nechoba, ngaphansi kwezitshalo ezahlukene ezimbozekile, ezisetshenziswa ngezindlela ezahlukene ezweni.. Amasampula omhlabathi aqoqwa ekujuleni okuhlukene ukuze kuqhathaniswe izizinda zehlathi kanye nezindawo ezitshalwe umoba. Imiphumela iveze umehluko ku-pH, okuqukethwe kwe-organic carbon (TOC), i-Al, i-Fe, ubumba, nokuqukethwe kodaka phakathi kwezindawo, nokutshalwa komoba okuthinta kakhulu i-BD ne-Ks. Kuyajabulisa ukuthi i-TOC iyakwazi ukulekelela ekugcinweni kwamanzi ngokwezinga elithile, izinto ezifana nobunjalo bento nomhlabathi ocoyisakele, kubaluleke kakhulu. Umhlabathi one-TOC ephakeme ubonise ukuhlanganisa okungcono, okubangele i-BD ephansi kanye ne-TP ephakeme, ngaleyo ndlela kuthuthukiswe i-Ks, FC, ne-PWP. Isimuncwane esishintshaniswayo kanye nenhlabathi ecoyisakele kuhlonzwe njengezinto ezibalulekile ekuhlanganisweni, lapho ukugxila kwe-Al ne-Fe kukhuphuka ngokutshalwa komoba kuzo zonke izilinganiso. Ucwaningo lugcizelela ukubaluleka kwezinqubo zokuphatha umhlabathi ukuze kuqinisekiswe ukukhiqizwa kwezolimo okusimeme kule nhlabathi. Iziphakamiso zifaka ukufaka umcako ukunciphisa ubumuncu bomhlaba kanye nokwenza ngcono ukutholakala kwesisekelo esishintshayo. Izenzo ezifana nokwengeza izinto eziphilayo, ukunciphisa ukulinywa komhlabathi, kanye nokushintshaniswa kwezitshalo kuphakanyiswa ukuthi kugcinwe noma kuthuthukiswe okuqukethwe kwe-TOC, ngaleyo ndlela kukhuthazwe ukuhlanganisa okuzinzile futhi kuvinjwe ukuwohloka kwenhlabathi. Ngokujwayelekile, imiphumela yocwaningo igqamisa ukusebenzisana okukhulu phakathi kokusetshenziswa komhlaba, izakhiwo zenhlabathi, kanye nezinqubo zokuphatha ekulolongeni ukusimama kwezinhlelo zezolimo enhlabathini enomswakama eNingizimu-Afrika.