Pub Date : 2021-03-15DOI: 10.1080/02571862.2021.1879287
Vhuthu Ndou, Frederick Eksteen, E. Phiri, P. Pieterse
Resistance to glyphosate in plantago (Plantago lanceolata L.), a serious weed in South Africa, was confirmed in 2003. More recently, a plantago biotype that is putatively resistant to both glyphosate and paraquat was reported. Seeds from a putatively susceptible (S) plantago population and from two putatively resistant populations (R1 and R2) were subjected to glyphosate and paraquat. To investigate possible multiple resistance, sequential application of glyphosate and paraquat was explored. The results showed an LD50 of 891.89 g a.e. ha−1 and 387.75 g a.i. ha−1 for glyphosate and paraquat respectively for the S biotype. For glyphosate, the LD50 value for R1 was 3842.61 g a.e. ha−1. The LD50 for the R2 biotype to glyphosate was 2020.39 g a.e. ha−1. The paraquat LD50 values for the R1 and R2 biotypes were 785.14 and 1246.43 g a.i. ha−1 respectively, resulting in resistance indices of 2 and 3 respectively. Sequential application of glyphosate and paraquat was not effective in plantago management. The R biotypes showed resistance to both glyphosate and paraquat indicating possible multiple resistance.
车前草(plantago lanceolata L.)是南非的一种严重杂草，2003年证实其对草甘膦具有抗性。最近，一种车前草生物型被认为对草甘膦和百草枯都具有抗性。对一个推定易感的车前草种群和两个推定抗性的车前草种群(R1和R2)的种子施用草甘膦和百草枯。为了调查可能的多重抗性，对草甘膦和百草枯的顺序施用进行了探索。结果表明，S型草甘膦和百草枯的LD50分别为891.89 g a.e. ha−1和387.75 g a.i. ha−1。对于草甘膦，R1的LD50值为3842.61 g a.e. ha−1。R2型对草甘膦的LD50为2020.39 g a.e. ha−1。R1和R2生物型的百草枯LD50分别为785.14和1246.43 g a.i. ha−1，抗性指数分别为2和3。连续施用草甘膦和百草枯对车前草的治理效果不明显。R型对草甘膦和百草枯均有抗性，表明可能存在多重抗性。
{"title":"First report of glyphosate and paraquat resistance in two Plantago biotypes","authors":"Vhuthu Ndou, Frederick Eksteen, E. Phiri, P. Pieterse","doi":"10.1080/02571862.2021.1879287","DOIUrl":"https://doi.org/10.1080/02571862.2021.1879287","url":null,"abstract":"Resistance to glyphosate in plantago (Plantago lanceolata L.), a serious weed in South Africa, was confirmed in 2003. More recently, a plantago biotype that is putatively resistant to both glyphosate and paraquat was reported. Seeds from a putatively susceptible (S) plantago population and from two putatively resistant populations (R1 and R2) were subjected to glyphosate and paraquat. To investigate possible multiple resistance, sequential application of glyphosate and paraquat was explored. The results showed an LD50 of 891.89 g a.e. ha−1 and 387.75 g a.i. ha−1 for glyphosate and paraquat respectively for the S biotype. For glyphosate, the LD50 value for R1 was 3842.61 g a.e. ha−1. The LD50 for the R2 biotype to glyphosate was 2020.39 g a.e. ha−1. The paraquat LD50 values for the R1 and R2 biotypes were 785.14 and 1246.43 g a.i. ha−1 respectively, resulting in resistance indices of 2 and 3 respectively. Sequential application of glyphosate and paraquat was not effective in plantago management. The R biotypes showed resistance to both glyphosate and paraquat indicating possible multiple resistance.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"134 - 139"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2021.1879287","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47245238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-15DOI: 10.1080/02571862.2020.1858512
P. F. Loke, Johannes Jacobus Schimper, E. Kotzé, C. D. du Preez
This study evaluated temporal effects of wheat production management practices on soil fertility under semi-arid conditions. Treatments applied for 37 years included straw management (unburned and burned), tillage practices (no-tillage, stubble mulch, and mouldboard ploughing) and weed control methods (chemical and mechanical). Soil samples were collected from 0–50, 50–150 and 150–250 mm layers, in 1990, 1999, 2010 and 2016, and analysed for organic carbon (OC), total nitrogen, pH, phosphorus (P) and potassium (K). Supplied grain yield data were used to estimate straw yield. Uptake of N, P and K by grain (removal) and straw (recycle) were estimated across sampling periods. Results revealed that OC, C:N ratio and P generally increased from 1990 to 1999 or 2010, and that conservation tillage increased soil fertility as compared with mouldboard ploughing. The only year × treatment interaction effects were on pH and K in the soil layers 0–50 and 50–150 mm in some treatments. However, all soil fertility indicators increased from 1990 to 1999 or 2010, then declined or stabilised across all treatments. The results suggest that adoption of conservation tillage with associated straw and nutrient recycling and additions cannot enable farmers to maintain or improve soil fertility and yields over time.
{"title":"Long-term wheat production management effects on soil fertility indicators in the semi-arid eastern Free State, South Africa","authors":"P. F. Loke, Johannes Jacobus Schimper, E. Kotzé, C. D. du Preez","doi":"10.1080/02571862.2020.1858512","DOIUrl":"https://doi.org/10.1080/02571862.2020.1858512","url":null,"abstract":"This study evaluated temporal effects of wheat production management practices on soil fertility under semi-arid conditions. Treatments applied for 37 years included straw management (unburned and burned), tillage practices (no-tillage, stubble mulch, and mouldboard ploughing) and weed control methods (chemical and mechanical). Soil samples were collected from 0–50, 50–150 and 150–250 mm layers, in 1990, 1999, 2010 and 2016, and analysed for organic carbon (OC), total nitrogen, pH, phosphorus (P) and potassium (K). Supplied grain yield data were used to estimate straw yield. Uptake of N, P and K by grain (removal) and straw (recycle) were estimated across sampling periods. Results revealed that OC, C:N ratio and P generally increased from 1990 to 1999 or 2010, and that conservation tillage increased soil fertility as compared with mouldboard ploughing. The only year × treatment interaction effects were on pH and K in the soil layers 0–50 and 50–150 mm in some treatments. However, all soil fertility indicators increased from 1990 to 1999 or 2010, then declined or stabilised across all treatments. The results suggest that adoption of conservation tillage with associated straw and nutrient recycling and additions cannot enable farmers to maintain or improve soil fertility and yields over time.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"93 - 106"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2020.1858512","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42367704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-15DOI: 10.1080/02571862.2021.1891473
CF Wessels, L. van Straaten, C. du Preez, G. Ceronio
Maize is the most important crop produced for human and animal nourishment in South Africa. The crop is susceptible to zinc (Zn) deficiencies, which result in lower grain yields with poorer nutritional value. Knowledge of the nature and behaviour of Zn fertilisers is therefore important for sustainable maize production, especially in sandy soils. The aim of this incubation study was to test the effect of inorganic (ZnO, ZnCl2, ZnCO3 and ZnSO4) and chelated (ZnEDTA, ZnDTPA, ZnEDDHA and ZnHEDTA) sources of Zn applied at different rates on Zn extracted by diluted HCl, DTPA, Mehlich-1, Ambic-2 and Na2EDTA methods. Analyses showed that ZnO was the least effective source, and ZnSO4 was the most effective source at increasing the extractable Zn of sandy soils. The extractable Zn content of the soils increased almost linearly with increasing application rates of all the zinc sources. Generally, the Na2EDTA method was most efficient in extracting the applied Zn. These results must be validated with crop growth response in glasshouse and especially field studies.
{"title":"A comparison of zinc sources and extraction methods on sandy soils suitable for maize cropping","authors":"CF Wessels, L. van Straaten, C. du Preez, G. Ceronio","doi":"10.1080/02571862.2021.1891473","DOIUrl":"https://doi.org/10.1080/02571862.2021.1891473","url":null,"abstract":"Maize is the most important crop produced for human and animal nourishment in South Africa. The crop is susceptible to zinc (Zn) deficiencies, which result in lower grain yields with poorer nutritional value. Knowledge of the nature and behaviour of Zn fertilisers is therefore important for sustainable maize production, especially in sandy soils. The aim of this incubation study was to test the effect of inorganic (ZnO, ZnCl2, ZnCO3 and ZnSO4) and chelated (ZnEDTA, ZnDTPA, ZnEDDHA and ZnHEDTA) sources of Zn applied at different rates on Zn extracted by diluted HCl, DTPA, Mehlich-1, Ambic-2 and Na2EDTA methods. Analyses showed that ZnO was the least effective source, and ZnSO4 was the most effective source at increasing the extractable Zn of sandy soils. The extractable Zn content of the soils increased almost linearly with increasing application rates of all the zinc sources. Generally, the Na2EDTA method was most efficient in extracting the applied Zn. These results must be validated with crop growth response in glasshouse and especially field studies.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"152 - 158"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2021.1891473","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48811397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-15DOI: 10.1080/02571862.2020.1863485
E. Asare, O. Domfeh, S. Avicor, P. Pobee, Y. Bukari, I. Amoako-Attah
Outbreak of anthracnose of cacao (Theobroma cacao L.), covering an estimated total growing area of 248.47 hectares, occurred in parts of Ghana from July to October 2019. Disease samples were collected from the outbreak areas to isolate and identify the pathogen and establish its pathogenicity. Disease symptoms appeared on leaves as dark brown patches with yellow halo margins. Colletotrichum gloeosporioides s.l. was isolated from infected plant tissues and pathogenicity tests confirmed it as the causative agent. The disease was widespread in the Prestea-Huni Valley district of the Western Region, particularly in the Yareyeya community, where a 14.8-hectare farm was seriously affected. Anthracnose has long been known as a sporadic but minor disease of cacao in Ghana. The current shift in status and rapid spread of the disease from infected farms to new farms, though it may or may not be contiguous, cannot be readily explained. Application of copper fungicides, namely Nordox 75 WG (86% cuprous oxide), Champion (77% cupric hydroxide) and Royal Cop 50 WP (77% copper hydroxide) at 75 g, 100 g and 100 g, respectively, each in 15 litres of water, at 2-week intervals for four months, effectively managed the disease.
{"title":"Colletotrichum gloeosporioides s.l. causes an outbreak of anthracnose of cacao in Ghana","authors":"E. Asare, O. Domfeh, S. Avicor, P. Pobee, Y. Bukari, I. Amoako-Attah","doi":"10.1080/02571862.2020.1863485","DOIUrl":"https://doi.org/10.1080/02571862.2020.1863485","url":null,"abstract":"Outbreak of anthracnose of cacao (Theobroma cacao L.), covering an estimated total growing area of 248.47 hectares, occurred in parts of Ghana from July to October 2019. Disease samples were collected from the outbreak areas to isolate and identify the pathogen and establish its pathogenicity. Disease symptoms appeared on leaves as dark brown patches with yellow halo margins. Colletotrichum gloeosporioides s.l. was isolated from infected plant tissues and pathogenicity tests confirmed it as the causative agent. The disease was widespread in the Prestea-Huni Valley district of the Western Region, particularly in the Yareyeya community, where a 14.8-hectare farm was seriously affected. Anthracnose has long been known as a sporadic but minor disease of cacao in Ghana. The current shift in status and rapid spread of the disease from infected farms to new farms, though it may or may not be contiguous, cannot be readily explained. Application of copper fungicides, namely Nordox 75 WG (86% cuprous oxide), Champion (77% cupric hydroxide) and Royal Cop 50 WP (77% copper hydroxide) at 75 g, 100 g and 100 g, respectively, each in 15 litres of water, at 2-week intervals for four months, effectively managed the disease.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"107 - 115"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2020.1863485","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47313236","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-15DOI: 10.1080/02571862.2021.1881634
R. M. Moloto, F. Dakora, P. Soundy, S. Maseko
Although the application of biostimulants to soils and plants affects their phosphatase activity, this has not been shown in chickpea (Cicer arietinum L.) grown under South African conditions. In this study, chickpea genotypes were grown in silty-loam and silty-clay-loam soils and supplied with Kelpak and Bontera. The leaves, roots and rhizospheric soil were collected, processed and acid phosphatase (APase) activity assayed following the p-nitrophenol method. The ICCV92944 cultivar exhibited the highest levels of intracellular activity in both soils and extracellular APase in the silty-loam soil. Leaves of the selected genotypes revealed increased APase activity than roots. The application of Kelpak increased intracellular APase activity while Bontera enhanced extracellular APase activity. The APase activity was markedly higher in chickpea grown in the silty-clay-loam soil compared to those grown in the silty-loam soil.
{"title":"Effects of biostimulants on tissue and rhizospheric acid phosphatase activity of chickpea genotypes","authors":"R. M. Moloto, F. Dakora, P. Soundy, S. Maseko","doi":"10.1080/02571862.2021.1881634","DOIUrl":"https://doi.org/10.1080/02571862.2021.1881634","url":null,"abstract":"Although the application of biostimulants to soils and plants affects their phosphatase activity, this has not been shown in chickpea (Cicer arietinum L.) grown under South African conditions. In this study, chickpea genotypes were grown in silty-loam and silty-clay-loam soils and supplied with Kelpak and Bontera. The leaves, roots and rhizospheric soil were collected, processed and acid phosphatase (APase) activity assayed following the p-nitrophenol method. The ICCV92944 cultivar exhibited the highest levels of intracellular activity in both soils and extracellular APase in the silty-loam soil. Leaves of the selected genotypes revealed increased APase activity than roots. The application of Kelpak increased intracellular APase activity while Bontera enhanced extracellular APase activity. The APase activity was markedly higher in chickpea grown in the silty-clay-loam soil compared to those grown in the silty-loam soil.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"180 - 183"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2021.1881634","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43487077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-03-15DOI: 10.1080/02571862.2021.1879286
A. Wood, A. D. Breeyen
The pathogen Colletotrichum acutatum J.H.Simmonds was developed in South Africa during the 1980s as a mycoherbicide to control invasive silky hakea (Hakea sericea Schrad. & J.C.Wendl.) and was subsequently widely used by a variety of land managers to induce gummosis disease. To determine persistence under natural conditions, disease incidence and severity were monitored annually at five sites in the Western Cape and Eastern Cape provinces, from 2008 until 2017. Disease incidence ranged between 12% and 95% of trees with gummosis in the first year. At four of the sites, high levels of mortality were recorded during the first four years of monitoring. In the year with the highest mortality, between 38 and 64% of trees were dead. No mortality was recorded at the fifth site. Disease incidence and mortality were reduced in the latter years, coinciding with drier conditions. At three of the sites, fires occurred once during the course of monitoring and the disease reappeared one to three years post-fire. It was concluded that although the disease will persist under natural conditions, for maximum benefit the fungus should be actively applied to maintain high levels of incidence and mortality. Depending on site characteristics and weather trends, this should be on an annual, bi- or triennial basis, or following fires or dry years.
{"title":"Incidence of gummosis disease in silky hakea under natural conditions in South Africa","authors":"A. Wood, A. D. Breeyen","doi":"10.1080/02571862.2021.1879286","DOIUrl":"https://doi.org/10.1080/02571862.2021.1879286","url":null,"abstract":"The pathogen Colletotrichum acutatum J.H.Simmonds was developed in South Africa during the 1980s as a mycoherbicide to control invasive silky hakea (Hakea sericea Schrad. & J.C.Wendl.) and was subsequently widely used by a variety of land managers to induce gummosis disease. To determine persistence under natural conditions, disease incidence and severity were monitored annually at five sites in the Western Cape and Eastern Cape provinces, from 2008 until 2017. Disease incidence ranged between 12% and 95% of trees with gummosis in the first year. At four of the sites, high levels of mortality were recorded during the first four years of monitoring. In the year with the highest mortality, between 38 and 64% of trees were dead. No mortality was recorded at the fifth site. Disease incidence and mortality were reduced in the latter years, coinciding with drier conditions. At three of the sites, fires occurred once during the course of monitoring and the disease reappeared one to three years post-fire. It was concluded that although the disease will persist under natural conditions, for maximum benefit the fungus should be actively applied to maintain high levels of incidence and mortality. Depending on site characteristics and weather trends, this should be on an annual, bi- or triennial basis, or following fires or dry years.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"126 - 133"},"PeriodicalIF":0.9,"publicationDate":"2021-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2021.1879286","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49292248","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/02571862.2020.1845829
AE Venter, C. du Preez
Large areas of alkaline and calcareous soils are irrigated in South Africa. For these soils, proper fertilisation programs based on soil phoshorus (P) analyses are required. Little is known about P analyses of alkaline and calcareous soils. The study aimed to compare P analyses by three laboratories, each using Bray 1, Mehlich 3 and Olsen extraction methods. Six soils with a pH of 7.1 to 8.2 that contain 0.6 to 12.4% of CaCO3 were incubated for two months after application of mono-ammonium phosphate (MAP) at levels equivalent to 0, 16.8, 33.6, 50.4, 67.2, 84.0 and 100.8 kg P ha−1, subjected to several wetting and drying cycles. The P contents that were reported differed in many instances between the laboratories. The differences were sometimes of such an extent that it will influence P fertiliser programs significantly. This should be a concern for farmers and their advisors. This is probably inter alia due to the chemical composition of the extractants. An in-depth investigation into a larger number of laboratories’ P analyses of alkaline and calcareous soils is warranted to confirm the results.
南非大面积的碱性和钙质土壤被灌溉。对于这些土壤，需要根据土壤磷(P)分析制定适当的施肥方案。人们对碱性和钙质土壤的磷分析知之甚少。该研究旨在比较三个实验室的P分析，每个实验室都使用Bray 1, Mehlich 3和Olsen提取方法。6种pH值为7.1至8.2、CaCO3含量为0.6至12.4%的土壤在施用磷酸一铵(MAP)后，分别以0、16.8、33.6、50.4、67.2、84.0和100.8 kg P ha - 1的水平孵育2个月，经历数次湿润和干燥循环。报告的磷含量在许多情况下不同的实验室。这种差异有时如此之大，以至于会显著影响磷肥的施用。这应该引起农民和他们的顾问的关注。这可能是由于萃取剂的化学成分造成的。有必要对大量实验室对碱性和钙质土壤的磷分析进行深入调查，以证实这一结果。
{"title":"A comparison of the results of phosphorus analyses of alkaline and calcareous soils amongst South African laboratories","authors":"AE Venter, C. du Preez","doi":"10.1080/02571862.2020.1845829","DOIUrl":"https://doi.org/10.1080/02571862.2020.1845829","url":null,"abstract":"Large areas of alkaline and calcareous soils are irrigated in South Africa. For these soils, proper fertilisation programs based on soil phoshorus (P) analyses are required. Little is known about P analyses of alkaline and calcareous soils. The study aimed to compare P analyses by three laboratories, each using Bray 1, Mehlich 3 and Olsen extraction methods. Six soils with a pH of 7.1 to 8.2 that contain 0.6 to 12.4% of CaCO3 were incubated for two months after application of mono-ammonium phosphate (MAP) at levels equivalent to 0, 16.8, 33.6, 50.4, 67.2, 84.0 and 100.8 kg P ha−1, subjected to several wetting and drying cycles. The P contents that were reported differed in many instances between the laboratories. The differences were sometimes of such an extent that it will influence P fertiliser programs significantly. This should be a concern for farmers and their advisors. This is probably inter alia due to the chemical composition of the extractants. An in-depth investigation into a larger number of laboratories’ P analyses of alkaline and calcareous soils is warranted to confirm the results.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"70 - 76"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2020.1845829","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43953403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-01-01DOI: 10.1080/02571862.2020.1845828
AE Venter, C. du Preez
Little research has been done on extractable phosphorus (P) in alkaline and calcareous irrigated soils of South Africa. This study aimed to quantify extractable P by selected methods in these soils after application of mono-ammonium phosphate (MAP) at different rates. Six soils with a pH of 7.1 to 8.2 that contained 0.6–12.4% CaCO3 were incubated for two months after application of MAP at levels equivalent to 0, 16.8, 33.6, 50.4, 67.2, 84.0 or 100.8 kg P ha−1. After incubation, soil P was extracted with the Olsen, Bray 1, Mehlich 3 and Ambic 1 methods. The most soil P was extracted with the Mehlich 3 method, and the least soil P was extracted with either the Bray 1 or Olsen methods, regardless of the MAP application rate. The differences in P extracted by the methods were attributed to the chemical composition of the extractants and the soil properties. Olsen and to a lesser extent Ambic 1 were the most reliable methods for establishing the amount of P required to raise the P status of the alkaline and calcareous soils. Future research should focus on establishing specific threshold values for soil and crop combinations with the Olsen method.
对南非碱性和钙质灌溉土壤中可提取磷的研究很少。本研究旨在以不同速率施用磷酸一铵(MAP)后，通过选定的方法定量测定这些土壤中可提取的磷。6种pH值为7.1至8.2、CaCO3含量为0.6-12.4%的土壤在施用MAP后分别以0、16.8、33.6、50.4、67.2、84.0或100.8 kg P ha - 1培养2个月。孵育后，采用Olsen、Bray 1、Mehlich 3和Ambic 1法提取土壤P。无论MAP施用量如何，Mehlich 3法提取的土壤磷最多，Bray 1法和Olsen法提取的土壤磷最少。不同方法提取磷的差异主要与提取剂的化学成分和土壤性质有关。Olsen和Ambic 1在较小程度上是确定提高碱性和钙质土壤磷状态所需磷量的最可靠方法。未来的研究应侧重于用Olsen方法建立土壤和作物组合的具体阈值。
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Pub Date : 2021-01-01DOI: 10.1080/02571862.2020.1829117
P. Malan, M. Tiawoun, Khumoetsile S Molatlhegi, S. Materechera
Woody plant encroachment is recognised as one of the major threats to biodiversity in ecosystems. In many arid and semiarid areas of South Africa, indigenous encroacher species are proliferating, but the factors that favor their abundance are poorly understood. This study investigated the effect of encroaching woody species on soil properties. The effects of two encroaching species, Senegalia mellifera and Dichrostachys cinerea, on soil nutrients and chemical properties were investigated in 8 communally managed grazing sites and compared to the effects of the non-encroacher, Vachellia karroo, in two non-encroached benchmark sites. Three belt transects were laid out to determine woody plant density. Three soil samples (0-20 cm deep) per belt were sampled to determine soil properties. Senegalia mellifera was the most abundant with a mean density of 5907 TE ha−1. Soil properties in the benchmark sites had no significant differences (p > 0.05) than soil under encroaching D. cinerea regarding organic C, total N, C:N, exchangeable Na, CEC, EC, ESP, SAR and soil texture. Plant influence on soil differed among encroaching species and between encroaching and non-encroaching species. Plant diversity explain the variation of soil properties and prove the important specific role of each species in the ecosystem.
木本植物的入侵是对生态系统生物多样性的主要威胁之一。在南非的许多干旱和半干旱地区，本土入侵物种正在激增，但人们对促进它们丰富的因素知之甚少。研究了木本植物入侵对土壤性质的影响。在8个共同管理的放牧区中，研究了两种入侵物种(Senegalia mellifera和Dichrostachys cinerea)对土壤养分和化学性质的影响，并与非入侵物种(Vachellia karroo)在2个非入侵基准放牧区的影响进行了比较。布设3个带样，测定木本植物密度。每个带采样3个土壤样品(0-20 cm深)以确定土壤性质。Senegalia mellifera最丰富，平均密度为5907 TE ha−1。在有机碳、全氮、C:N、交换性钠、CEC、EC、ESP、SAR和土壤质地等方面，基准样地土壤性质与灰羊草侵蚀样地差异不显著(p < 0.05)。植物对土壤的影响在入侵种和非入侵种之间存在差异。植物多样性解释了土壤性质的变化，并证明了每种物种在生态系统中的重要具体作用。
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Pub Date : 2021-01-01DOI: 10.1080/02571862.2020.1844325
A. Franke
This paper provides a systematic review of studies assessing the impact of climate change on crop yields in southern Africa. Moreover, it synthesises the current knowledge of the impact of elevated ambient CO2 levels (eCO2) and temperatures on physiological processes, and the application of this knowledge in mechanistic crop models. While eCO2 evidently has a strong impact on photosynthesis and crop water use, it is uncertain how this will work out for the climatic and crop management conditions prevailing in southern Africa. The impact of heat stress on crop reproductive processes and the process of transpiration cooling mitigating heat stress are poorly represented in models, while both process are relevant given the climatic conditions prevailing in southern Africa. Twenty studies assessing the impact of climate change on future yields of crops, mostly maize, have been retrieved. The results suggest that potato, Bambara groundnut and sugarcane yields may improve. No consistent trends for maize and sorghum could be identified. While yield predictions are obviously context-specific, large uncertainties related to climate predictions and crop models imply results should be treated with caution. Suggestions are made for field experimentation and the improved application of crop models for climate change research in the region.
{"title":"Assessing the impact of climate change on crop production in southern Africa: a review","authors":"A. Franke","doi":"10.1080/02571862.2020.1844325","DOIUrl":"https://doi.org/10.1080/02571862.2020.1844325","url":null,"abstract":"This paper provides a systematic review of studies assessing the impact of climate change on crop yields in southern Africa. Moreover, it synthesises the current knowledge of the impact of elevated ambient CO2 levels (eCO2) and temperatures on physiological processes, and the application of this knowledge in mechanistic crop models. While eCO2 evidently has a strong impact on photosynthesis and crop water use, it is uncertain how this will work out for the climatic and crop management conditions prevailing in southern Africa. The impact of heat stress on crop reproductive processes and the process of transpiration cooling mitigating heat stress are poorly represented in models, while both process are relevant given the climatic conditions prevailing in southern Africa. Twenty studies assessing the impact of climate change on future yields of crops, mostly maize, have been retrieved. The results suggest that potato, Bambara groundnut and sugarcane yields may improve. No consistent trends for maize and sorghum could be identified. While yield predictions are obviously context-specific, large uncertainties related to climate predictions and crop models imply results should be treated with caution. Suggestions are made for field experimentation and the improved application of crop models for climate change research in the region.","PeriodicalId":21920,"journal":{"name":"South African Journal of Plant and Soil","volume":"38 1","pages":"1 - 12"},"PeriodicalIF":0.9,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/02571862.2020.1844325","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44730299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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