Soil indicator data from a Conservation Agriculture trial in Eastern Cape, South Africa
The data was generated from the analysis of the soil samples that were collected from the conservation agriculture (CA) trial in Phandulwazi, Eastern Cape, South Africa. The experimental design for the treatments used was a split-split plot design. Standard soil extraction and analytical methods were used to generate the data. The tillage treatments were the conventional tillage (CT) and no-till (NT) and the residue management treatments were designated as follows: R+ as crop residue retention and R- as crop residue removal. The crop rotation treatments were maize-fallow-maize (MFM), maize-fallow-soybean (MFS), maize-wheat-maize (MWM) and maize-wheat-soybean (MWS).
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Soil indicators were quantified using standard field and laboratory procedures and techniques in soil science. Bulk density (pb) was determined using a core sampler with a known volume and mass. Three samples were collected from each plot. Excess soil was trimmed and soil samples were dried at 105 ◦C for 24 h and the dry mass were weighed to calculate bulk density. This was done in all plots at 0 – 5 cm and 5 – 10 cm depths. For the determination of all other soil indicators, soil samples were collected using a graduated 1.9 cm diameter core sampler. Six soil cores were collected randomly from each plot per depth interval to make a composite sample. Soil samples were air dried, ground to pass through a 2 mm sieve, bagged and stored at 4 ◦C before analysis. These samples were used for the determination of other soil indicators. Macro-aggregate stability was determined using a modified fast wetting method. Particle size fractions (sand, silt, clay) were measured by using the hydrometer procedure. Soil pH was determined with a pH meter in a 1:2.5 (ν/ν) soil: water suspension. Electrical conductivity (EC) was measured with a conductivity meter in the same suspension used for pH reading after a 1 h settling period. Exchangeable Na, K, Ca, and Mg were extracted using ammonium acetate and analyzed using an Inductively Coupled Plasma Emission Spectrograph (ICP–OES) (Varian 710-ES). Inorganic N was determined by extracting nitrate and ammonium in 5 g of soil using potassium sulphate. The extracts were analyzed for nitrate and ammonium on a UV spectrophotometer. Soil P was determined by extracting P in soils with the Olsen method and P concentrations were measured on a UV spectrophotometer. Total soil carbon (C) was determined in the air-dried soil samples by dry combustion using the LECO (Truspec CNS analyzer). Total C was assumed to be only soil organic C (SOC) because of samples having no carbonate-rich minerals. Microbial biomass carbon (MBC) was determined using standard soil fumigation and chemical extractions procedures. β‑Glucosidase activity was measured by colorimetric determination of p‑nitrophenyl that is released when 1 g air-dried soil was incubated with 1 mL of p‑Nitrophenyl‑β‑D‑glucoside (PNG) and 4 mL of buffer solution (pH 6.0) at 37 ◦C for 1 h.