Effects of site preparation for afforestation on soil properties and greenhouse gas emission

Forest plantations in the UK are often established on seasonally waterlogged peaty gley soils which often require site preparation (drainage and mounding) to lower the water table and prepare planting positions. Substantial changes in the physical environment of peaty gley soils can accompany site preparation including fluctuations in soil temperature and soil moisture. These and other changes can all affect soil properties and decomposition processes and well as the dynamics of CO2, CH4 and N2O. A field experiment was established at Harwood Forest (NE England) to investigate the effects of three site management practices (drainage, mounding and fertilisation) frequently used for afforestation and replanting on peaty gley soils in the UK on soil properties and various of C and N, environmental variables (soil temperature, water content and water table height) and emissions of CO2, CH4 and N2O. The relationship between GHG emissions and environmental variables was also examined. The experiment was laid out in a factorial split-plot design. Drainage decreased C and N concentration in the 10 cm soil layer. The soil bulk density in the 0 to 20 cm soil layer was increased by mounding. Drainage and fertilisation increased soil CO2 efflux, whereas mounding did not affect soil CO2 efflux. All three practices affected soil CH4 fluxes with drainage reducing the fluxes and mounding and fertilisation increasing the fluxes. Nitrous oxide emissions were significantly affected by mounding and fertilisation, with mounding decreasing emissions and fertilisation increasing emissions. Soil temperature was the main environmental factor controlling soil respiration in this site. Over the two years study drainage and fertilisation increased the total greenhouse budget by 13.1% and 97.9%, while mounding caused a reduction of−17.6%. Drainage plus mounding reduced the total greenhouse budget by 6.9%, while drainage plus mounding plus fertilisation increased the total greenhouse budget by 101.8%. There is a potential for up-scaling GHG emissions from newly drained peaty gley for inclusion in the UK Land Use Land-Use Change and Forestry (LULUCF) Greenhouse Gas Inventory. However up-scaling and evaluation of the net emissions requires high quality data from different sites newly drained for afforestation. More studies are needed if net fluxes from newly drained sites are to the included in the LULUCF Greenhouse Gas Inventory

Seed characteristics and the influence of scarification treatments on the germination of Pterocarpus angolensis in Botswana

Pterocarpus angolensis, a vital timber tree species of the Miombo and other woodlands, is native to eastern and southern Africa. Gemination studies were carried out at the Botswana University of Agriculture and Natural Resources to ascertain the seeds’ features and find the most effective scarification treatments that yield the fastest, highest, and most consistent germination of P. angolensis. Ten seed pretreatments were included in the completely randomized design of the experiments. These treatments included nicking, immersion in boiling water for one, three, and five minutes, concentrated sulphuric acid for fifteen, thirty, forty-five, and sixty minutes, and hot water left to cool overnight. Treated seeds were allowed to germinate at room temperature (25 °C) for 30 days. An analysis of variance (ANOVA) was performed on the raw data. The findings demonstrated that nicking and sulfuric acid treatments significantly increased seed germination (p=0.0001) compared to untreated seeds. The germination rate of the seeds emersed in boiling water for one, three, and five minutes was noticeably lower than that of untreated seeds. Because of their tough seed coat, P. angolensis seeds must be pretreated before sown. This study found that nicking and sulphuric acid treatment were the best techniques for seed germination of P. Angolensis

Application and Use of Presowing Treatment Methods to Improve Germination of Vachellia karroo (Hayne) Banfi & Galasso

A germination experiment of Vachellia karroo seeds was conducted at the Botswana University of Agriculture and Natural Resources, Department of Crop and Soil Sciences laboratory, from September to October 2018. Seeds were collected along the Segoditshane River in Gaborone to investigate the effect of different pre-sowing treatment methods on their germination. The experiment was laid out in a completely randomized design (CRD) with five treatments (control, mechanical scarification, boiling water, hot water and concentrated sulphuric acid (98.8%). Boiling water (30, 60, 180 and 300 seconds) and concentrated sulphuric acid (15, 30, 45 and 60 minutes) had four levels of exposure time. The highest significant (p < 0.01) cumulative germination percentages were recorded in seeds subjected to sulphuric acid for 45 and 60 minutes, mechanical scarification (shortest germination mean time of 2.0-2.3) and boiling water at 30 and 60 seconds (moderate germination mean time of 5-5.9) whereas, the control treatment had the least cumulative germination percentage of 2%. As expected, the same trend was revealed for germination index. The seeds possess seed coat imposed dormancy, which requires sowing treatments. The best treatments for releasing dormancy in V. karroo were sulphuric acid and mechanical scarification and because of the risks associated with the use of sulphuric acid, the researchers recommend mechanical scarification as the suitable treatment method in tree nurseries.Keywords: Seed dormancy, Germination mean time, Germination index, Pre-sowing treatment, Germination percentage, Germination rate, Tree nursery

Dimensional Relations and Physical Properties of Wood of Acacia saligna, an Invasive Tree species growing in Botswana

Abstrac

Evaluating the growth response of Cassia abbreviata oliv

Abstrac

Effect of Seed Pre-sowing Treatment on Germination of Three Acacia Species Indigenous to Botswana

Effectiveness of selected immersion-based seed pre-sowing treatments (cold water, hot water and concentrated sulphuric acid) on the germination of three Acacia species (A. tortilis, A. erioloba, and A. nigrescens) was studied between December 2012 and January 2013. For each species, four treatments (including the control) were replicated four times in a Completely Randomized Design. Percentage germination, germination mean time (GMT) and germination index (GRI) were calculated and the data were subjected to analysis of variance (ANOVA). Significant differences in germination were observed across the treatments. Concentrated sulphuric acid significantly (P < 0.01) increased the germination percentages of A. erioloba (87%) and A. nigrescens (30%) while the control, cold water and hot water treatments significantly (P < 0.01) reduced their germination percentages (5%). However, treating A. tortilis with hot water for 9 min significantly (P < 0.01) enhanced its germination percentage (30%) compared to the other treatments. As expected the control had the highest GMT, although this was not significant for A. tortilis. The GRI revealed similar trend as germination percentages across the treatments for the three Acacia species. Based on these results, we recommend concentrated sulphuric acid and hot water as suitable seed pre-treatments for enhancing the germination of the three Acacia species

Effects of site preparation for afforestation on soil properties and greenhouse gas emission

Forest plantations in the UK are often established on seasonally waterlogged peaty gley soils which often require site preparation (drainage and mounding) to lower the water table and prepare planting positions. Substantial changes in the physical environment of peaty gley soils can accompany site preparation including fluctuations in soil temperature and soil moisture. These and other changes can all affect soil properties and decomposition processes and well as the dynamics of CO2, CH4 and N2O. A field experiment was established at Harwood Forest (NE England) to investigate the effects of three site management practices (drainage, mounding and fertilisation) frequently used for afforestation and replanting on peaty gley soils in the UK on soil properties and various of C and N, environmental variables (soil temperature, water content and water table height) and emissions of CO2, CH4 and N2O. The relationship between GHG emissions and environmental variables was also examined. The experiment was laid out in a factorial split-plot design. Drainage decreased C and N concentration in the 10 cm soil layer. The soil bulk density in the 0 to 20 cm soil layer was increased by mounding. Drainage and fertilisation increased soil CO2 efflux, whereas mounding did not affect soil CO2 efflux. All three practices affected soil CH4 fluxes with drainage reducing the fluxes and mounding and fertilisation increasing the fluxes. Nitrous oxide emissions were significantly affected by mounding and fertilisation, with mounding decreasing emissions and fertilisation increasing emissions. Soil temperature was the main environmental factor controlling soil respiration in this site. Over the two years study drainage and fertilisation increased the total greenhouse budget by 13.1% and 97.9%, while mounding caused a reduction of−17.6%. Drainage plus mounding reduced the total greenhouse budget by 6.9%, while drainage plus mounding plus fertilisation increased the total greenhouse budget by 101.8%. There is a potential for up-scaling GHG emissions from newly drained peaty gley for inclusion in the UK Land Use Land-Use Change and Forestry (LULUCF) Greenhouse Gas Inventory. However up-scaling and evaluation of the net emissions requires high quality data from different sites newly drained for afforestation. More studies are needed if net fluxes from newly drained sites are to the included in the LULUCF Greenhouse Gas Inventory.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The impact of livestock grazing management systems on soil and vegetation characteristics across savanna ecosystems in Botswana

The objective of this study was to determine the impact of livestock grazing management systems on soil and vegetation dynamics under different environmental conditions of Botswana. Soil and vegetation were randomly sampled along transects located in three ranches and adjacent communal grazing land in 2009 and 2010. Our results showed that grazing management systems did not consistently affect soil texture, organic carbon, pH and bulk density. The soil characteristics such as soil carbon and clay content were strongly associated with variation in rainfall, and contributed to improved rangeland condition characterised by high herbaceous biomass and low bush encroachment. Livestock grazing management systems do not impact soil and vegetation properties differently as indicators of degradation are observed in both grazing systems. Thus, there is a need to develop a sustainable land management model that will improve soil carbon, increase herbaceous biomass and generally improve the condition of rangelands in Botswana.Keywords: cattle, grassland, grazing, land degradation, rangeland conditio

Pastoralists' Perception and Ecological Knowledge on Savanna Ecosystem Dynamics in Semi-arid Botswana

We investigated vegetation dynamics in relation to livestock grazing as perceived by pastoral farmers in different regions of Botswana. A structured questionnaire was used to collect farmers' understanding of vegetation changes and causes within three different grazing lands. The pastoral farmers' description of dominant vegetation differed significantly both at the local and district level, which suggests that rangelands consist of patches dominated by different grasses and woody vegetation. Most pastoralists indicated that grass composition has undergone changes, and unpalatable grasses such as Aristida congesta and Megaloprotachne albescens are increasing. The different factors perceived by pastoral farmers to cause changes in vegetation composition included rainfall, overgrazing, and fire. Bush encroachment is considered to be more common in communal grazing land than in ranches. According to pastoral farmers, the ranching system is less degrading to the environment and more sustainable for livestock production than is communal grazing

Agronomic Performance of Sorghum after Panicle Removal

A field study was conducted at Botswana College of Agriculture (BCA) farm to investigate the effect of panicle removal and no panicle removal on growth, yield and yield components of grain sorghum within and across landraces. The experiment was arranged in a complete randomized block design (CRBD), three landraces, two management practices and four replications. The sorghum landraces; segaolane, korwane and mmamokotane designated (T1-T3) represent management practice 1 (panicle removed) whereas controls designated (C1-C3) represent management practice 2 (panicle not removed) were planted in an area of 63 m2. Within landraces, treated (panicle removed) plants revealed significantly (P<.05) lower plant height, number of tillers and grains per head across the landraces. Overall, a non-significant (P<.05) treatment effect was observed for total grain weight and shoot biomass. Untreated plants (panicle not removed) significantly (P<.01) increased the harvest index in segaolane whereas a non-significant treatment effect was observed for korwane and mmamokotane. Across landraces, panicle removal significantly (P<.05) enhanced mmamokotane plant height and shoot biomass whereas it significantly (P<.01) increased the number of grains per head in segaolane. Panicle removal significantly (P<.01) increased total grain, 1000 seed weight and harvest index in korwane whereas a non-significant treatment effect was observed for number of tillers across the landraces. It is concluded that panicle removal is ineffective management practice for enhancing growth, yield and yield components in sorghum landraces. &nbsp