Mineralogy and Fertility Status of Selected Soils of the Eastern Cape Province, South Africa

Abstract

Thorough knowledge of cultivated soils is necessary for their informed and sustainable management. This study was carried out to gain a better understanding of cropped soils in the Eastern Cape Province of South Africa. The mineralogical and chemical composition and nutrient status of topsoils collected from homestead gardens and fields of smallholdings in 5 of the 36 magisterial districts where smallholder farming prevails in the Province were determined. These data were supplemented with results of soil analyses conducted by an Analytical Services Laboratory that obtains its samples from the 31 magisterial districts where largescale farms are dominant. The soils studied were similar mineralogically, and all had 2431 a clay fraction that was dominated by quartz, mica, and/or kaolinite, which is fairly typical for many tropical and subtropical soils. Elemental analysis showed that the soils were generally low to very low in their total content of nutrients, except for sulfur (S), manganese (Mn), zinc (Zn), copper (Cu), and boron (B), reflecting the marine and sedimentary nature of their parent materials. The available nutrient status of the cultivated soils was generally low to very low, especially those found in smallholder fields. This was attributed to low soil organic matter levels and low geological reserves of some nutrients notably phosphorus (P), potassium (K), and calcium (Ca), coupled with continuous cultivation of the lands without adequate nutrient replenishment. Depending on location, 75 -100% of the fields tested low in pH, 62 -100% were low in organic carbon, 83 -100% were low in extractable K, 62 -93% were low in extractable Ca, and 79 -100% were deficient in available phosphorus. The nutrient status of soils receiving moderate to high amounts of nutrients was generally satisfactory, as revealed by the nutrient content of garden soils found on smallholdings and the fields on large-scale farms. In all cases, soil pH was low to critically low. The findings are used to propose a soil fertility management strategy for the communal areas of the Province.

Status of Underutilised Crops in South Africa: Opportunities for Developing Research Capacity

“…In contrast, the smallholder sector comprised more than 1.4 million small family farms that occupied less than 14 million ha. Communal agriculture is largely within the former homelands, which are characterised by degraded soils due to poor soil and water management practices [17]. Consequently, agricultural productivity has been declining over time [18].…”

Biomass production, weed suppression, nitrogen and phosphorus uptake in white oat (Avena sativaL.) and grazing vetch (Vicia dasycarpaL.) cover crop bicultures under an irrigated no-till system

“…The soil at the initiation of the experiment had a pH (H 2 O) of 5.9, a saturated paste electrical conductivity of 0.14 d Sm −1 , total C and N was 1.1% and 0.087%, respectively, and inorganic P (Bray 1) was 2.01 mg kg −1 . The soil type is sandy loam with 64.2% sand, 16.0% silt and 19.8% clay (Mandiringana et al 2005). …”

“…Although both grazing vetch and white oat (Avena sativa L.) can symbiotically interact with arbuscular mycorrhizal fungi, increasing phosphorus (P) uptake, legumes decompose Introduction faster, because of lower C:N ratios than grasses leading to improved availability of P for the follow-on crop (Xin et al 2005). Hence, legume cover crops have the potential to improve yields of follow-on crops in the EC where low levels of N and P are a major constraint to improved crop productivity, particularly maize, the staple crop (Mandiringana et al 2005, Fanadzo et al 2009). …”

Persistence of the pesticidalBacillus thuringiensisprotein expressed in Bt maize plant materials in two soils of the Central Eastern Cape, South Africa

“…The soil at the University of Fort Hare farm was the allu-vial type (Oakleaf form in S.A. classification), with high mica (2: 1 mineral) and low kaolinite, hematite and quartz (Mandiringana et al, 2005). The land had rotations of fallow periods with irrigated lucerne during the previous five years.…”