Alternative substrates for cultivating oyster mushrooms (Pleurotus ostreatus)

Wheat straw has generally been used as the main substrate for cultivating oyster mushrooms (Pleurotus ostreatus); however, in South Africa it is becoming expensive for small-scale farmers to utilise. Therefore, the main objective of the study was to investigate the use of alternative, but suitable substrates for planting oyster mushrooms. Wheat straw (control), wood chips and thatch grass, selected on account of their year-round availability and low cost, were tested with two drainage treatments (drained or not drained) and replicated four times. Wheat straw showed no contamination, whereas there was contamination in thatch grass and wood chips from weeks 1 to 4. At harvest, a significantly higher cumulative number of flushes, caps and fresh mass of oyster mushrooms was observed in wheat straw and thatch grass compared with wood chips. The results demonstrated that thatch grass could be used as a viable alternative to the commonly used wheat straw.ARC–ITSC and AgriSETA.http://www.tandfonline.com/loi/tjps202016-12-30hb201

Flooding and Phytophthora cinnamomi : effects on photosynthesis and chlorophyll fluorescence in shoots of non-grafted Persea americana (Mill.) rootstocks differing in tolerance to Phytophthora root rot

Please read abstract in the article.The Hans-Merensky Foundation and the National Research Fund (NRF) through the THRIP programme (Department of Science and Technology, South Africa).http://www.elsevier.com/locate/sajbhj201

Deriving crop coefficients for evergreen and deciduous fruit orchards in South Africa using the fraction of vegetation cover and tree height data

DATA AVAILABILITY: The authors do not have permission to share data.Please read abstract in the article.The Hydrosciences Research Group in the Smart Places cluster at the Council for Scientific and Industrial Research (CSIR) of South Africa and the Water Research Commission of South Africa.https://www.elsevier.com/locate/agwatPlant Production and Soil Scienc

Changes in phosphorus status of 'Cripps' Pink' apple trees after application of mulches

The effect of four different mulches on fruit quality was quantified, either directly via mineral nutrient contributions or indirectly, by increasing nutrient uptake efficiency in the soil. We hypothesised that fruit nutrient levels would increase more when an organic mulch, containing nutrients, was applied to the soil, with smaller/no increases when an inorganic mulch was applied to the tree row. In this paper, we concentrate on changes in fruit phosphorus (P) concentrations after application of five treatments: a clean cultivated control, an inorganic woven geotextile fabric, and organic mulches – compost, wood chips and a vermi-castings/ wood chips combination. The trial was conducted on a commercial farm, Lourensford Estate, South Africa, from October 2008 to April 2012 – on an adjacent light, sandy and heavier, sandy-silt soil. Mineral nutrient analyses of the soil, leaves, mulches and fruit were performed. Yield and fruit size were determined. Soil temperatures and soil water status were recorded hourly during the last two seasons. P concentrations did increase chronologically from the soil, then into leaves and then into the fruit after application of mulches that provided additional P to the soil. Sporadic increases in both leaves and fruit occurred, but could not always be related to treatment effects. The significant consistent increase of P levels of the vermi-castings treatment in the heavy soil is likely to be a combination of reduced irrigation volumes, as well as a treatment effect. All mulches resulted in the well-established buffering of soil temperatures, soil water content and percentage soil carbon. Based on results from this study, it is not feasible to apply mulches for the sole purpose to increase P levels in the soil, leaves or fruit of established trees – although increases were noticed from time to time. In addition to water and temperature modifying effects of mulches that would differ between soil textures and depend on the mulch source, increases in P concentrations may result. As yield efficiency is still the primary factor determining income per hectare for the producer, the decrease in yield that resulted from mulching under these conditions, will still outweigh any positive contributions of mulches. It is therefore of utmost importance to first adjust irrigation volumes to a mulch treatment before the advantageous properties of mulching will be of value.Stellenbosch University and HortgroScience.http://www.actahort.orgam201

Are simple empirical crop coefficient approaches for determining pecan water use readily transferrable across a wide range of conditions?

The accurate estimation of evapotranspiration (ET) of orchard crops is critical for judicious irrigation water management and planning. However, it is impossible to measure ET under all possible combinations of climate and management practices, which necessitates the use of ET models. Although empirical models are more likely to be adopted by consultants and growers, due to easier parameterization and the requirements for fewer, more easily measured input parameters, they may not always be transferable across a wide range of conditions. As a result these models may not always give acceptably accurate ET values outside of the area in which they were calibrated. This study therefore aimed to evaluate empirical crop coefficient models for pecans in two different orchards which differ in climate and/or fractional canopy cover from where the models were developed. When testing the FAO-56 approach it was found that pecans should not be grouped under stone fruit and that a six stage crop growth should be considered, instead of the traditional four stage curve. Improved accuracy in estimating ET of pecans could, however, be achieved by using a pecan specific reference crop coefficients for a mature orchard and scaling this with fractional canopy cover for different orchards, provided that an adjustment was made for the influence of climate on canopy development. This was achieved by using a published growing degree (GDD) day crop coefficient relationship, provided seasonal accumulated thermal time is below 1600 GDD and that crop coefficients do not exceed 1.1.The Water Research Commission (Project K5/1770) with co-funding from the National Department of Agriculture, Forestry and Fisheries of South Africa.http://www.actahort.orgam2017Plant Production and Soil Scienc

Crop coefficient approaches based on fixed estimates of leaf resistance are not appropriate for estimating water use of citrus

The estimation of crop water use is critical for accurate irrigation scheduling and water licenses. However, the direct measurement of crop water use is too expensive and time consuming to be performed under all possible conditions, which necessitates the use of water use models. The FAO-56 procedure is a simple, convenient and reproducible method, but as canopy cover and height vary greatly among different orchards, crop coefficients may not be readily transferrable from one orchard to another. Allen and Pereira (2009) therefore incorporated a procedure into the FAO-56 approach which estimates crop coefficients based on a physical description of the vegetation and an adjustment for relative crop stomatal control over transpiration. Transpiration crop coefficients derived using this procedure and fixed values for citrus, did not provide good estimates of water use in three citrus orchards. However, when mean monthly leaf resistance was taken into account, good agreement was found with measured values. A relationship between monthly reference evapotranspiration and mean leaf resistance provided a means of estimating mean leaf resistance which estimated transpiration crop coefficients with a reasonable degree of accuracy. The use of a dynamic estimate of mean leaf resistance therefore provided reasonable estimates of transpiration in citrus.South Africa‟s Water Research Commission (Project K5/1770, Water use of fruit tree orchards), with cofounding from the South African National Department of Agriculture, Forestry and Fisheries.http://link.springer.com/journal/2712016-12-30hb201

Modelling water use of subtropical fruit crops : the challenges

Subtropical fruit crops form an important part of the fruit industry in many countries. Many of these crops are grown in semi-arid regions or subtropical regions where rainfall is seasonal and as a result the vast majority of these perennial, evergreen orchards are under irrigation. This represents a significant irrigation requirement and with more emphasis being placed on the conservation of water and orchard profitability, it is becoming increasingly important to accurately estimate water use of these crops and schedule irrigation accordingly. The FAO-56 procedure is a simple, convenient and reproducible method for estimating water use. However, the transferability of crop coefficients between different orchards and growing regions is not always readily achieved, due largely to differences in canopy size and management practices. In addition, as subtropical crops tend to exhibit a higher degree of stomatal control over transpiration than most other agricultural crops, some measure of canopy or leaf resistance must be taken into account when using models based on atmospheric demand. The challenge is therefore to provide reliable and dynamic estimates of canopy resistance from relatively simple parameters which can be of use to irrigation consultants and farmers for determining the water requirements of these crops. The challenge remains to ensure that these dynamic estimates are realistic and readily applicable to a number of growing regions. The derivation of transpiration crop coefficients, based on canopy cover and height and a dynamic estimate of leaf resistance, provided reasonable estimates of transpiration in three orchards in contrasting climates, suggesting that this approach could prove useful in future for subtropical crops.http://www.actahort.org2018-05-10hj2017Plant Production and Soil Scienc

The seasonal regulation of gas exchange and water relations of field grown macadamia

Please read abstract in the article.South Africa’s Water Research Commission and Macadamias South Africa NPC.http://www.elsevier.com/locate/scihorti2021-06-01hj2021Plant Production and Soil Scienc

Measurement and modelling of water use by high yielding apple orchards and orchards of different age groups in the winter rainfall areas of South Africa

Apple production for the export market is in South Africa entirely dependent on irrigation. In recent years, high performing orchards yielding up to 120 t of fruit ha-1 are becoming common in a country where the average yield is between 60 and 80 t ha-1. This raises important questions regarding the sustainability of the exceptionally high yields given the limited availability of water for irrigation. Moreover, there is also no accurate quantitative information published on water use by apple orchards of different age groups and this compromises efficient irrigation scheduling. The aim of this study was to quantify water use by high yielding apple orchards and orchards of different age groups. Data were collected in four commercial orchards, two planted to non-bearing ‘Cripps’ Pink’ and ‘Golden Delicious’ apples and another two highyielding full-bearing orchards of these cultivars. Transpiration in the full-bearing orchards was measured using the heat pulse velocity sap flow method. Granier probes were used on the young non-bearing trees. Orchard evapotranspiration (ET) was measured using eddy covariance systems during selected periods. Ancillary data which included the orchard microclimate, stomatal resistance, soil water content and soil evaporation were also collected. The full-bearing ‘Golden Delicious’ orchard (22- year-old) had the highest seasonal transpiration of 785 mm, followed by the fullbearing ‘Cripps’ Pink’ (9-year-old) which transpired 587 mm. The non-bearing ‘Cripps’ Pink’ (3-year-old) transpired 272 mm compared to 198 mm for the nonbearing ‘Golden Delicious’ (2-year-old). The data were used to validate a dual source ET model based on the Shuttleworth-Wallace method. Transpiration of full-bearing orchards was accurately predicted by the model with the RMSE of 0.55 mm d-1 for ‘Cripps’ Pink’ and 0.70 mm d-1 for the ‘Golden Delicious’ orchards. Improvements to the substrate evaporation sub-model are required to account for various orchard floor management practices.The research reported here formed part of a bigger project entitled “Quantifying water use by high performing apple orchards in the winter rainfall areas of South Africa” project no WRC K5/2398.The Water Research Commission (WRC), with additional funding from Hortgro Science, through the South African Apple and Pear Producers Association (SAAPPA) in South Africa.http://www.actahort.orgam2017Plant Production and Soil Scienc

Estimating the water requirements of high yielding and young apple orchards in the winter rainfall areas of South Africa using a dual source evapotranspiration model

Exceptionally high yielding (>100 t ha−1) apple orchards (Malus domestica Borkh.) are becoming common in South Africa and elsewhere in the world. However, no accurate quantitative information currently exists on the water requirements of these orchards. Information is also sparse on the water use of young apple orchards. This paucity of data may cause inaccurate irrigation scheduling and water allocation decisions, leading to inefficient use of often limited water resources. The aim of this study was therefore to investigate the dynamics of water use in eight apple orchards in South Africa planted to Golden Delicious and the red cultivars i.e. Cripps’ Pink, Cripps’ Red and Rosy Glow in order to understand how canopy cover and crop load influence orchard water use. Four of the orchards were young (3–4 years after planting) and non-bearing, while the other four were mature high yielding orchards. Transpiration was monitored using sap flow sensors while orchard evapotranspiration (ET) was measured during selected periods using eddy covariance systems. Scaling up of ET to seasonal water use was done using a modified Shuttleworth and Wallace model that incorporated variable canopy and soil surface resistances. This model provided reasonable estimates in both mature and young orchards. The average yield in the two mature ‘Cripps’ Pink’ was ∼110 t ha−1 compared to ∼88 t ha−1 in the ‘Golden Delicious’ orchards. However, average transpiration (Oct-Jun) was ∼638 mm for the ‘Cripps’ Pink’ and ∼778 mm in the ‘Golden Delicious’ orchards. The peak leaf area index was ∼2.6 and ∼ 3.3 for the mature ‘Cripps’ Pink and ‘Golden Delicious’ orchards. So, canopy cover rather than crop load was the main driver of orchard water use. Transpiration by the young orchards ranged from 130 to 270 mm. The predicted seasonal total ET varied from ∼900 to 1100 mm in the mature orchards and it was ∼500 mm in the young orchards. Orchard floor evaporation accounted for ∼18 to 36% of ET in mature orchards depending on canopy cover and this increased to more than 60% in young orchards.The Water Research Commission of South Africa (Project no WRC K5 2398//4), the South African Apples and Pears Producers Association and the South African Parliamentary Grant to the CSIR on Water Security (Project number ECHS043).http://www.elsevier.com/locate/agwat2019-09-30hj2018Plant Production and Soil Scienc