Parallel B: Planted Pastures

Importance of the southern African members of tribe Phaseoleae (Leguminosae) in pasture development Phaseoleae is the largest tribe in the Leguminosae family, indigenous to southern Africa. It contains 22 genera, namely Alistilus, Bolusafra, Canavalia, Decorsea, Dipogon, Dolichos, Dumasia, Eriosema, Erythrina, Flemingia, Galactia, Lablab, Macrotyloma, Mucuna, Neonotonia, Neorautanenia, Ophrestia, Otoptera, Rhynchosia, Sphenostylis, Teramnus and Vigna. Many species within these genera are known for their high forage value. These species include, but are not limited to Lablab purpureus, Neonotonia wightii and Vigna unguiculata. Therefore, the Phaseoleae tribe may hold potential in developingmore new forage species. To describe the 180 species within this tribe in terms of their adaptation or range of tolerance to rainfall, mean annual rainfall and mean annual minimum and maximum temperature, soil pH and phosphorus levels, a discriminant analysis was performed to determine which predictor contributed mostly to species distribution as recorded by PRECIS (2008). Eriosema and Rhynchosia contains large species numbers (46 and 59 respectively) and were analysed separately from the other 75 remaining species. The section of the data for Eriosema, Rhynchosia and Vigna spp. Mean annual rainfall, mean annual minimum temperatures and soil phosphorus (P) content were the main drivers for the distribution of Eriosema into three groups. Most species were grouped in Group 1, i.e. high annual rainfall, intermediate minimum temperature and soil P, indicating a limited distribution range. The main drivers for the separation of Rhynchosia species into four groups are mean annual rainfall, soil pH and mean annual minimum temperature. Many of the Rhynchosia spp. were recorded in all four groups, suggesting a high tolerance to these given independent variables. The remaining species, with Vigna the largest group (20 spp.), were driven by mean annual rainfall and soil pH. The majority of Vigna spp. were grouped in Group 3, recorded in high annual rainfall and intermediate soil pH regions. Results show that discriminant analyses can be used to group species in the tribe Phaseoleae in terms of measured variables to determine firstly, their range of tolerance and secondly, to use this as a selection tool for further screenings to select indigenous legume species with desirable attributes.

Endophytes are all micro-organisms that live inside host plants partly or wholly throughout their life cycle without causing any apparent harm or disease but may form beneficial associations with the host. A study was conducted to understand endophytic fungal communities inhabiting the aerial and root tissues of local Brachiaria grass ecotypes grown in natural habitat after a four-month dry spell in early 2018 from a grazing field of the International Livestock Research Institute’s Headquarters in Nairobi, Kenya. A total of 20 whole plant samples of Brachiaria grass were collected. Fungal endophytes were isolated from surface disinfected, asymptomatic leaf, leaf sheath, and root tissues of Brachiaria grass on Potato Dextrose Agar amended with an antibiotics cocktail. Fungal DNA was extracted using MagAttract 96 DNA plant core kit and fungi were identified to the lowest possible taxonomic unit using ITS rDNA sequence analysis. Our previous study on the fungal endophytes of local Brachiaria grass in the year with normal weather conditions isolated 354 fungi representing 84 different fungal taxa. The current study characterizes the fungal community of Brachiaria grass during the dry weather condition, estimates species diversity and elucidates potential role of these microbes in growth and development of Brachiaria grass, including the adaptation to drought and low fertility soils. Moreover, we will compare the results obtained from current and previous study that differ in weather condition.

Forage chicory (Cichorium intybus) and Plantain (Plantago lanceolata) collectively known as forage herbs, have recently become regular components of mainly dairy pastures. On most farms the forage herbs are planted in a mixture with grasses and often clover species are added as a minor component. Trials were conducted at Outeniqua Research Farm on mixtures of forage herbs with grass, compared with pure stands planted in spring (5/10/2016) and autumn (15/3/2017) using a 4x4 balanced lattice design. Dry matter (DM) yield and botanical composition on a biomass basis, were determined. The spring-planted trial had a substantial weed component of 37% to 65% at the first harvest treatment dependent. By January 2017 the weeds decreased to a mean of 28% for the herb treatments and 84% for the grass only treatments. The autumn-planted trial had a mean of 13% weeds at the first harvest, decreasing from there onwards. During the first summer the grass component was outcompeted by the forage herbs while the forage herb pure stands had the highest yields (p< 0.05) with chicory yielding best with 8.0 tDM ha-1. From autumn 2017 onwards, all treatments with plantain, pure and mixed, out yielded (p< 0.05) the chicory treatments and pure grass treatments, including the second summer. The chicory treatments were higher yielding (p< 0.05) than the grass treatments. For the grass/herb mixtures the herb component dominated with 71% to 97% depending on the mixture. At 38.7 tDM ha-1 plantain had the highest DM yield over the 17-month period. The highest chicory yield was 32.1 tDM ha-1 and was lower (p< 0.05) than the plantain. The pure grass treatments were lower (p< 0.05) than all other treatments with a mean of with 20.6 tDM ha-1. In the autumn-planted trial the perennial ryegrass component dominated and out-yielded in both the pure stands and in a mixture with forage herbs until the end of winter. During spring the forage herb treatments were higher yielding (p< 0.05) than perennial ryegrass while during summer the pure plantain treatments yielded a mean of 8.4 tDM ha-1, which was higher than all other treatments. The same was true for the total DM yield, with plantain sown at 10kg ha-1 producing 22.0 tDM ha-1 during a 12-month period and perennial ryegrass at 15.3 tDM ha-1. In the autumn-planted mixtures the grass-component was smallest at the end of January with 5%. The pure stands of forage herbs yielded significantly better than the mixtures. In terms of pasture systems and how forage herbs can best be used, these results indicate that there could be merit in rather planting a pure forage herb sward and a grass pasture separately where both are grazed alternatively during the same day to ensure sufficient fibre from the grass pasture to counter the low DM content and high carbohydrate content of the forage herbs.

The sustainability of current nitrogen (N) fertilisation regimes for minimum-tillage kikuyu-ryegrass (Pennisetum clandestinum, Lolium multiflorum) pastures in the southern Cape are under scrutiny. The reason is that these guidelines were developed for conventional tillage and non-grazing systems. Thus, the aim was to determine effects of N fertilisation rates on soil and pasture characteristics. Nitrogen treatments were applied to a kikuyu-annual ryegrass trial site (four replicates, 225 m2 plots) at Outeniqua Research Farm for two years. Nitrogen fertiliser was applied after each grazing cycle (28 to 35 days) at five fixed rates namely 0, 20, 40, 60 and 80 kg N ha-1 (N0, N20, N40, N60 and N80). Prior to each grazing cycle by dairy cows, soil and pasture production characteristics were determined while botanical composition was determined seasonally. Response of total mineral N in soil to N treatments varied (P<0.05) between grazing cycles. Total mineral N in the 0–100 mm soil depth increased (P<0.05) over time in high N treatments (N60 and N80) compared to N0, for which it remained relatively constant throughout the trial period. This was also evident for the 100–200 mm and 200–300 mm depths. These findings indicate a build-up of N in soil to a point beyond what can be utilised by pasture and an increased risk of leaching when N is applied at ≥60 kg ha-1 grazing cycle-1. Pasture production response to N fertilisation was similar (P≥0.05) for all grazing cycles. Treatment N60 and N80 had, on average, a greater (P<0.05) pasture production compared to N0 treatment; however, this was not the case during all seasons. Pasture production was most negatively affected (P<0.05) during winter and autumn season. The ryegrass component was greatest (P<0.05) during winter and spring. All N-containing treatments had a greater (P<0.05) ryegrass component than the N0 treatment. Season and treatment affected (P<0.05) the pasture crude protein (CP) content, where high N treatments was greater (P<0.05) relative to low N treatments. Results suggest that N fertilisation rates should be adjusted according to season. Furthermore, in order to prevent N losses through leaching, while maintaining a high pasture production and quality, it is advisable to apply no more than N40 after each grazing during winter and spring. Interestingly, applying N20 after each grazing during summer and autumn will result in a similar pasture production as when applying N80. In addition N20 will ensure more acceptable pasture CP content for grazing dairy cows and induce a mineral N content in the soil that is less likely to result in N leaching. Lower N rates during summer might be due to the kikuyu component, which was greater (P<0.05) during summer and autumn, regardless of the N application. This may indicate sufficient soil N for pasture growth and is supported by a volunteer legumes component that was present in low N treatments, particularly in spring and summer. This, together with a potential to mineralise N (15-70 kg ha-1 grazing cycle-1) could have contributed to adequate N amounts for pasture growth during summer.  

A limitation to the uptake of kikuyu-temperate grass/legume pastures in the southern Cape is the reported 60% decline in total annual pasture dry matter (DM) yield compared with kikuyu-ryegrass pastures. Strategic nitrogen (N) fertilisation, based on applying nitrogen at lower rates or during specific times, could address this shortcoming. The aim of this study was to determine the effect of N application rates on the pasture production potential of irrigated kikuyu when over-sown with different grass/legume mixtures over a 3-year period. The four mixtures consisted of red clover (Trifolium pratense), white clover (T. repens) and one of four temperate grasses viz. Italian ryegrass (IC; Lolium multiflorum), perennial ryegrass (PC; L. perenne), Tall Fescue (FC; Festuca arundinacea) or cocksfoot (CC; Dactylis glomerata). The experiment was a randomised complete block design, with treatments randomly allocated within each block. Pastures were over-sown on an annual basis using a mulcher and Aitcheson seeder. Nitrogen was applied at 0, 20 and 40 kg of N ha-1 (N0, N20, N40, respectively) after each grazing. Pasture yield (kg DM ha-1) was determined every 28 to 35 days by cutting four 0.25 m2 quadrats to a height of 50 mm per plot before grazing. The mixture over-sown did not affect total annual DM production at the respective fertilisation rates during the three years. The IC mixture was the only mixture where fertilisation rate had an impact on total annual DM production, with the yield of the N0 treatment lower than N20 and N40 for year 1only. Mean annual N efficiency (kg of DM kg-1 of N applied) was greater (P< 0.05) for N20 than N40 for all mixtures over the 3-year period. Agronomic nitrogen efficiency (kg of DM relative to N0 kg-1 N applied) however, did not differ. With the exception the N0 treatments and the N20 treatment of FC during Spring of year 2, clover content was below 30% (recommended to obtain a benefit from legume content) for all seasons during the study. The only notable effect on sown grass content (%) was the greater (p< 0.05) ryegrass content of the N20 and N40 treatments than that of N0 in the IC mixture during winter and spring. The sown grass content in FC was lower (p< 0.05) than for other mixtures, irrespective of N rate and season. This mixture also had a higher (p>0.05) “weedy” volunteer grass content (Bromus spp. during winter and Paspalum notatum during summer and autumn) than other treatments, particularly during winter and spring. This component increased for all treatments from winter to autumn, being particularly high during summer and autumn (40-83%). With the exception of year 1, the kikuyu content in pastures remained below 15% from winter to summer for all treatments, and below 20% during autumn. These results indicate that previously kikuyu based pastures have been replaced by pastures dominated by volunteer or weedy grasses. This is likely to have confounded N treatment and mixture effects. To obtain the full benefit from temperate grasses and clover, these systems will have to undergo complete renovation/re-establishment to remove competition from volunteer and weedy grasses. Where over-sowing is the only option, IC is recommended.