A. T.P. Bennie

An assessment of the core-break method for estimating rooting density of different crops in the field

Abstract Most of the methods available for plant rooting studies in field soil are very tedious and time-consuming. Several investigations have shown that the core-break technique, in which roots are counted that appear at the faces of a broken core of soil, provides acceptable estimates of root length density in some situations. We investigated the usefulness of the core-break technique for evaluating rooting density of four plant species in two soil types. We encountered several problems, but recommend the core-break method to researchers who wish to quantify root development rapidly under various soil tillage practices.

Factors affecting runoff and soil loss under simulated rainfall on a sandy Bainsvlei Amalia soil

This study was conducted on a long-term tillage experiment that was designed to evaluate appropriate tillage practices for sustainable dryland crop production. Measurements of runoff and soil loss were conducted on a sandy Bainsvlei Amalia soil (88.0% sand, 3.6% silt, and 8.4% clay) with a rainfall simulator on three tillage practices, namely no-tillage (NT), stubble mulch (ST) and conventional tillage (CT), each combined with four levels of wheat residue cover. The measurements were replicated twice for each of the three tillage practices on 1 m2 area plots. The simulator used for the study produced raindrops at a constant intensity of 60 mm h-1 with a veejet type nozzle, which had kinetic energy comparable to natural rainfall. A sharp decline in runoff and soil loss occurred with an increase in residue ground cover from bare to about 70%, above which the effect was less dramatic. Generally, runoff and soil loss was higher on NT plots compared with ST and CT plots. It is recommended that a crop residue covering at least 70% should be maintained on the soil surface when conservation tillage is practiced to ensure higher infiltration and lower runoff on this type of soil. Tilling the soil to a depth of at least 150 to 250 mm below the mulch gave the lowest runoff and soil loss.

Concentration, accumulation and uptake rate of macro-nutrients by winter wheat under irrigation

The objective of this study was to obtain information on the nutrient uptake patterns of winter wheat (Triticum aestivum L.) grown under normal irrigation farming conditions. Except for irrigation scheduling, 13 farmers were allowed to follow their normal farming practices. At each site biomass production, nutrient content of the top growth and root length were measured regularly throughout the growing season, starting 35–45 days after planting. The nutrient content of the soils was determined on samples collected 35–45 days after planting at 300-mm depth intervals to a depth of 1.8 m. As early as 40 days after planting the concentration of N, P and Ca in wheat plants started to decrease, while the concentration of K, Mg and S started to decrease 10–20 days later. Accumulation of the nutrients in plants increased until 120 days after planting and then stabilized at an average of about 214, 40, 326, 33, 21 and 18 kg ha−1 for N, P, K, Ca, Mg and S, respectively. Nutrient uptake rates reached a maximum betwe...

Advances in soil physics and soil water management research in South Africa, 1979–2003

(2004). Advances in soil physics and soil water management research in South Africa, 1979–2003. South African Journal of Plant and Soil: Vol. 21, No. 5, pp. 268-277.

Transport of bromide in the Bainsvlei soil: Field experiment and deterministic/stochastic model simulation. I. Continuous water application

A field-scale tracer study was carried out in a sandy loam Bainsvlei soil of South Africa. The objectives were to study the leaching of solutes in this soil and analyse the result using deterministic and stochastic solute transport models. A rainfall simulator was used to apply water and solution on an area 100 by 100 cm at a flux rate of 5.41 mm/h. A neutron probe access tube was drilled at the centre of the plot to a depth of 200 cm. Four tensiometers were installed at 30, 45, 90, and 120 cm depths. After steady-state condition was attained, a conservative tracer Br– was then applied as KBr at a rate of 13.5 g Br/m2. Soil samples were taken 10 times at 20-cm depth intervals to a depth of 160 cm and Br– concentration was analysed using ion chromatography. Transport parameters were determined using a convection–dispersion equation (CDE) and the stream tube model (STM). The average Br– mass recovery was almost 100%. The average pore-water velocity determined from soil water balance was 2.08 cm/h. Pore-water velocities determined with CDE and STM were 2.24 cm/h and 2.20 cm/h, respectively. Bromide velocities of peak concentration and solute centre of mass were 2.05 cm/h and 2.02 cm/h, respectively. Generally, these results indicate that the Br– moved almost as a piston flow in this soil. The deterministic CDE and the stochastic STM performed almost equally well in estimating the transport parameters.

Tillage-crop residue management and rainfall-runoff relationships for the Alemaya catchment in Eastern Ethiopia

A field study was conducted in the Alemaya catchment, Eastern Ethiopia, with the objective of determining the effect of tillage practices, crop reside cover and rainfall characteristics on runoff during two rainfall seasons on a clayey Regosol with 5% slope. Relationships between runoff and rainfall characteristics, such as the amount, intensity and erosivity were established from a two-year data set. The results on fields without crop showed that a minimum of 21 ha−1 of fresh wheat residue is required to reduce runoff from low intensity storms and 4 t ha−1 of residue for high intensity storms with peak intensities of more than 55 mm h−1. These norms can be used for estimating runoff under comparable soil and climatic conditions. A technique was also developed to estimate runoff from the rainfall intensity-duration curve and the mean soil infiltration rate.

Concentration, accumulation and uptake rate of Cu, Fe, Mn and Zn by wheat under irrigation

The objective of this study was to obtain information on the Cu, Fe, Mn and Zn uptake patterns of wheat (Triticum aestivum L.) grown under normal irrigation farming conditions. Except for irrigation scheduling, the 13 farmers on whose farms the study was conducted were allowed to follow their normal farming practices. At each site biomass production and nutrient content of the top growth were measured regularly throughout the growing season, starting 35–45 days after planting. The concentration of Cu and Zn started to decrease from 40 days after planting, while the concentration of Fe and Mn increased until 50 days after planting and then started to decrease. Accumulation of Cu, Fe, Mn and Zn in the whole plant reached a maximum during caryopsis at about 150 days after planting. The maximum accumulation for Cu, Fe, Mn and Zn was 145, 3 984, 934 and 124 g ha−1, respectively. Uptake rates for Cu, Fe and Mn reached a maximum just before anthesis at about 115 days after planting. The maximum uptake rate for Z...

Bromide movement and uptake under bare and cropped soil conditions at Dire Dawa, Ethiopia

The worst-case scenario of NO3-N leaching is often determined using conservative tracers since it undergoes complex and interdependent transformations in the soil. However, few tracer studies have hitherto been done under cropped soil conditions. In this study, a field experiment was conducted to compare Br- transport under bare and maize planted soil conditions at the experimental site of the Alemaya University, Dire Dawa (East Ethiopia). At the beginning of the experiment, KBr was applied in a solution form. Soil and plant samples were taken several times during the growing season and the concentration of Br- determined. At the end of the experimental period, Br- peak was transported to depths of 900 mm and 1300 mm on bare and maize plots respectively. The percentage of Br- recovery from bare and maize plots was 99.8% and 86.8% respectively. Bromide velocity was slightly higher than the pore-water velocity. The maize plants took up about 8.1% of the applied bromide. The concentration of Br- in the plant tissue decreased as the crop grew while the total uptake was increasing.

Nutrient inflow to the roots of irrigated wheat throughout the growing season under semi-arid climatic conditions

The objective of this study was to obtain information on the inflow of N, P, K, Ca, Mg, S, Cu, Fe, Mn and Zn to the roots of wheat (Triticum aestivum L.) grown under normal irrigation farming conditions. Except for irrigation scheduling, the eight farmers on whose farms the study was conducted were allowed to follow their normal farming practices. At each site biomass production, nutrient content of the top growth and root length were measured regularly throughout the growing season, starting 35–45 days after planting. The inflow of all ten nutrients increased with the age of the crop, reaching a maximum somewhere between four fully unfolded leaves and anthesis, whereafter it decreased. The maximum inflow values for N, P, K, Ca, Mg and S were respectively, 113.0, 17.7, 187.0, 17.1, 8.9 and 8.3 μg m−1day−1. In the case of Cu, Fe, Mn and Zn the maximum inflow values were 46.4, 1 493.4, 249.8 and 68.3 ng m−1day−1 respectively. In the period when maximum inflow occurs, namely, 70–110 days after planting, the ...