Quantification of long-term precipitation use efficiencies of different maize production practices on a semi-arid ecotope in the Free State Province

Precipitation use efficiency (PUE) was estimated for four production practices, i.e. conventional tillage with November planting (CTN), conventional tillage with January planting (CTJ), in-field rainwater harvesting with November planting (WHBN), and in-field rainwater harvesting with January planting (WHBJ), over 80 maize seasons for a semi-arid ecotope in the central Free State Province of South Africa. An empirical yield prediction model was used to obtain maize grain yields. PUE was expressed as the ratio of transpiration: rainfall for each growing season (PUET), while transpiration was calculated from total biomass yield, vapour pressure deficit and a transpiration efficiency coefficient for maize. The following equation, based on 10 years of measured data, was developed to estimate daily vapour deficit pressure for the 80 seasons from daily maximum temperature: Vd = 0.163 x Tmax – 2.88 (R2 = 0. 73). Mean PUET values over the 80 seasons were: 0.260 for CTN, 0.320 for WHBN, 0.334 for CTJ, and 0.400 for WHBJ. These results confirmed and quantified the advantage of in-field rainwater harvesting over conventional tillage, and the advantage of January planting over November planting. PUET results were also expressed as cumulative probability functions. Significance tests showed that PUET for in-field rainwater harvesting was significantly better than PUET for conventional tillage, and that January planting was significantly better than November planting. It was concluded that the advantage of in-field rainwater harvesting over conventional tillage was mainly due to the absence of runoff and reduced evaporation in the former practice. The use of a short-growing cultivar, which flowers during the month with the most favourable climate, i.e. March, probably resulted in the advantage of January planting over November planting

Is tibial tuberosity-trochlear groove distance an appropriate measure for the identification of knees with patellar instability?

PURPOSE - Tibial tuberosity-trochlear groove distance (TT-TG) has been regarded as a useful tool for establishing therapeutic choices for patellar instability. Recently, it has been shown that TT-TG negatively correlated with the quadriceps angle, suggesting that if used individually, neither provide a valid measure of instability. This study aimed to compare TT-TG distance between both knees in patients with unilateral instability to assess whether this measurement is a decisive element in the management decisions for patellar instability. METHODS - Sixty-two patients (18 male and 44 female), reporting to a specialist patella clinic for recurrent unilateral patellar instability, were included in the study. Patients underwent bilateral long leg computed tomography scan to determine TT-TG distance in both knees. Tibial TT-TG in symptomatic and asymptomatic knees in the same individual was compared statistically. RESULTS - Mean TT-TG distance in the symptomatic knee was 16.9 (±4.9) mm, compared to 15.6 (±5.6) mm in the asymptomatic knee. Tibial TT-TG was not significantly different between stable and unstable knees (n.s.). CONCLUSIONS - The lack of difference in TT-TG distance between stable and unstable knees suggests that TT-TG distance alone may not be a decisive element in establishing therapeutic choices for patellar instability. It should, therefore, be interpreted with caution during clinical evaluations. LEVEL OF EVIDENCE: II

Is tibial tuberosity-trochlear groove distance an appropriate measure for the identification of knees with patellar instability?

PURPOSE - Tibial tuberosity-trochlear groove distance (TT-TG) has been regarded as a useful tool for establishing therapeutic choices for patellar instability. Recently, it has been shown that TT-TG negatively correlated with the quadriceps angle, suggesting that if used individually, neither provide a valid measure of instability. This study aimed to compare TT-TG distance between both knees in patients with unilateral instability to assess whether this measurement is a decisive element in the management decisions for patellar instability. METHODS - Sixty-two patients (18 male and 44 female), reporting to a specialist patella clinic for recurrent unilateral patellar instability, were included in the study. Patients underwent bilateral long leg computed tomography scan to determine TT-TG distance in both knees. Tibial TT-TG in symptomatic and asymptomatic knees in the same individual was compared statistically. RESULTS - Mean TT-TG distance in the symptomatic knee was 16.9 (±4.9) mm, compared to 15.6 (±5.6) mm in the asymptomatic knee. Tibial TT-TG was not significantly different between stable and unstable knees (n.s.). CONCLUSIONS - The lack of difference in TT-TG distance between stable and unstable knees suggests that TT-TG distance alone may not be a decisive element in establishing therapeutic choices for patellar instability. It should, therefore, be interpreted with caution during clinical evaluations. LEVEL OF EVIDENCE: II

Evaluating the use of iron-coated tubes for wetland delineation in South Africa: A pilot study in the Kruger National Park

The identification of hydric soils is important for wetland delineation and protection.  South Africa currently uses the Department of Water Affairs and Forestry (DWAF) wetland delineation guidelines which can be subjective in certain contexts.  A robust technical standard that can be legally conclusive is therefore required and should be developed for South African conditions.  The National Technical Committee of Hydric Soils (NTCHS, 2007) in the United States of America has accepted the Indicator of Reduction in Soils (IRIS) tube methodology as a technical standard, but this had not yet been tested in South Africa.  It is proposed that the NTCHS (2007) be adapted for use in South Africa. These Fe-coated tubes are installed into the soil and if reducing conditions are present, the Fe coating is removed.  The aim of this study was to evaluate the use of IRIS tubes as a technical standard for wetland delineation in South Africa. The study took place in three different wetland systems (Malahlapanga, Nshawu and the Tshuthsi spruit) in the Kruger National Park.  Piezometers were installed in triplicate in each zone, and the water table, pH and Eh were recorded monthly. Soils were classified, soil wetness indicators identified, and vegetation described.  The study took place from September 2012 to August 2013.  The areal percentage of paint removed from the top 300 mm of the IRIS tubes was quantified by scanning the tubes and then compared to the DWAF wetland indicators. It was found that the DWAF indicators and the IRIS tube method were mostly in agreement; however, the conditions at the Tshutshi spruit were not favourable for Fe reduction, and hence the use of IRIS tubes, due to the high pH values recorded.  The IRIS tubes were therefore a useful tool for wetland delineation in the majority of conditions, but are not recommended in high pH, sodic environments.  Further research is recommended over a wider geographical area as well as testing the MIRIS methodology (Manganese Indicators of Reduction in Soils) in wetlands that would inhibit Fe reduction

Estimation of runoff at Glen in the Free State Province of South Africai

Reliable runoff estimation is important for simulating long-term crop yields in semi-arid areas. It requires reliable data including soil and rainfall characteristics. This paper aims to simulate runoff for each rainfall event on the Glen/Tukulu ecotope, in central South Africa, using annual runoff data measured over 18 years (1937 to 1955) on a conventional tilled soil, annually planted to maize, and a bare untilled soil. Runoff calculated for these two treatments provides information needed to simulate long-term crop yields using conventional tillage and in-field water harvesting. The PutuRun model was used to stochastically disaggregate daily rainfall data into shorter duration rainfall intensities and to simulate runoff for each rainfall event during a particular season. The simulated runoff data were summed for each season and compared with the observed annual runoff values during the respective years to evaluate the performance of the model. The model was calibrated using half of the data and validated using the rest. Calibration was carried out by running the model a number of times with a different set of input parameter values, until acceptable results were obtained. The following statistical results were obtained for the validation tests: for the maize plots index of agreement (d) = 0.85, root mean square error (RMSE) = 24 mm, mean absolute error (MAE) = 18 mm, systematic RMSE (RMSEs) = 16 mm, unsystematic RMSE (RMSEu) = 17 mm, and coefficient of determination (r2) = 0.58; and for the bare plots d = 0.90, RMSE = 51 mm, MAE = 48 mm, RMSEs = 13 mm, RMSEu = 49 mm, and r2 = 0.74. It is concluded that the PutuRun Model can be used with reasonable confidence after calibration to simulate long-term runoff on conventionally tilled, and bare untilled plots on the Glen/Tukulu ecotope using daily rainfall data. This procedure is expected to yield satisfactory results on other ecotopes with similar soil, slope, and rainfall characteristics. Key words: Glen, modelling, PutuRun, runoff Water SA Vol.31(1) 2005: 17-2

Relationships between agronomic and environmental phosphorus analyses of selected soils

Phosphorus (P) is an essential nutrient in crop production and is therefore typically applied as phosphatic fertilisers.  This can induce soil P concentrations that may contribute to freshwater eutrophication.  Soil P tests developed from a water pollution protection perspective are unlike those developed for agronomic purposes and are also not easily adapted to routine analyses.  The aim with this study was therefore to establish whether the values of P extracted from a range of soils by various agronomic and environmental P determination methods are related or not.  Topsoil samples were collected from virgin soils in central South Africa and treated with KH2PO4 to induce different P concentrations and then incubated for 3 months, while subjected to various wetting and drying cycles.  The samples were then analysed for P using the extractants of Bray 1, citric acid, ISFEI, Olsen, and Truog, commonly employed to establish the agronomic P status of soils.  Environmental P status was determined with calcium chloride (CaCl2) and ammonium oxalate (DPSox) extractants.  Generally good relationships were found between CaCl2 and ISFEI (R2 = 0.72), between DPSox and Truog (R2 = 0.79), and between DPSox and citric acid (R2 = 0.82).  Agronomic P soil tests therefore have the potential to be used in regulating application of phosphatic fertilisers to ensure optimum crop yields, while simultaneously limiting freshwater pollution.  Further field studies are, however, recommended to determine threshold values from an environmental point of view

Association of trochlear dysplasia with degenerative abnormalities in the knee: data from the Osteoarthritis Initiative

OBJECTIVE: To evaluate trochlear morphology as a potential risk factor for patellofemoral osteoarthritis, determined by morphological and quantitative measurements of cartilage degeneration using 3T magnetic resonance imaging (MRI) of the knee. MATERIALS AND METHODS: MR images of right knees of 304 randomly selected subjects, aged 45–60 years, from the Osteoarthritis Initiative (OAI) progression cohort were screened for trochlear dysplasia, defined by an abnormal trochlear depth. Out of 304 subjects, n=85 demonstrated a shallow trochlea (depth ≤3mm; 28%). In these, and also in a random sample of controls with normal trochlear depth (n=50), the facetal ratio and the sulcus angle were calculated and knee structural abnormalities were assessed by using a modified Whole-Organ-MR-Imaging Score (WORMS). Cartilage segmentation was performed and T(2) relaxation times and patellar cartilage volume were determined. ANOVA and multivariate regression models were used for statistical analysis of the association of MRI structural measures and trochlear morphology. RESULTS: Knees with a shallow trochlea showed higher patellofemoral degeneration (WORMS mean ±standard deviation, 11.2±0.5 versus 5.7±0.6; Multivariate regression, P<0.001) and lower patellar cartilage volume than controls (900±664mm(3) versus 1671±671mm(3); P<0.001). Knees with an abnormal medial-to-lateral facetal ratio (<0.4) showed increased patellofemoral WORMS scores (12.3±0.9 versus 8.3±0.5; P<0.001). Knees with an abnormal sulcus angle (>170°) also showed increased WORMS scores (12.2±1.1 versus 8.6±0.6; P=0.003). T(2) values at the patella were significantly lower in the dysplasia group with a shallow trochlea. However, significance was lost after adjustment for cartilage volume (P=0.673). CONCLUSION: Trochlear dysplasia, defined by a shallow trochlea, was associated with higher WORMS scores and lower cartilage volume, indicating more advanced osteoarthritis at the patellofemoral joint