|dc.description.abstract||ENGLISH ABSTRACT: The study was done (2014 = year 1 and 2015 = year 2) at the Langgewens Research Farm of the Western Cape Department of Agriculture near Moorreesburg (33o17’00” S, 18o42’00” E; 191 m). The aim of this study was to evaluate the effect of a once-off strategic tillage operation with a mouldboard plough or tine implement within different crop rotation systems on mineral-N levels of soils, soil moisture content, biomass production, chlorophyll content of leaves, stomatal conductance, light interception, initial and final root mass, reproductive components, seedling survival, weed seed bank, grain yield and grain quality of spring wheat (Triticum aestivum L) and canola (Brassica napus). Medic (Medicago) biomass and root mass was recorded during year 2.
The experimental design was a split-plot employed as a randomised complete block design. Three cropping sequences namely: medic/clover-wheat-medic/clover-wheat (McWMcW), wheat-lupin-wheat-canola (WLWC) and lupin-wheat-canola-wheat (LWCW) were allocated to main plots and replicated four times in year 1. The same plots were used during year 2 but due to crop rotation the cropping sequences were WMcWMc, WCWC and LWCW. The last letter in the sequence represents the crop on the field at the time of data collection. Tillage treatments were allocated to subplots namely: (a) continuous no-till (NT), soil left undisturbed until planting, (b) non-inversion tillage, with a tine (DT) to a depth of 400 mm and (c) inversion tillage with a mouldboard plough (MP) to a depth of 250 mm. The seed were planted with a tined no-till planter with knife openers. Plant and soil samples were collected every 30 days from a day before planting until harvesting and the relevant parameters determined. The study area was managed as a no-till system under the cropping systems mentioned above since 2000 and no stubble were removed from the research area since 2007.
Soil water content (SWC) and soil mineral nitrogen content (NH4+-N + NO3- -N) were determined one day before planting and every 30 days thereafter until harvesting. Soil water content in McWMcW was not influenced by tillage at all sampling dates during year 1. Significant differences were however recorded in LWCW with MP and DT that resulted in an increase in SWC during June and July of year 1. During year 2, NT resulted in higher (P=0.05) SWC 90 days after planting in LWCW compared to MP and DT. Soil water content was not influenced by tillage in either WMcWMc or WLWC for both years 1 and 2, 90 days after planting.
Soil mineral nitrogen was not influenced by tillage in McWMcW and LWCW during year 1. There were however significant differences recorded during year 2 with MP and DT increasing mineral nitrogen content 60 and 120 days after planting in LWCW. Tillage did not influence mineral nitrogen content during year 1 in WLWC, however, in year 2 mineral nitrogen content was significantly increased. Tillage treatments did not resulted in significant differences in mineral nitrogen content during year 2 in WMcWMc. Tillage treatments resulted in a higher amount of mineral nitrogen in McWMcW compared to the other sequences during year 1.
Glomalin content is an indicator of mycorrhizal growth. During year 1 DT significantly increased the glomalin content. It is concluded that a disruptive effect of DT and MP did not have a negative effect on SWC, mineral nitrogen or glomalin content.
During year 1 no significant differences (P=0.05) were recorded for the effect of tillage on light interception (LI), chlorophyll content (CC), stomatal conductance (SC) and initial root mass (IRM) in LWCW and McWMcW. Final root mass (FRM) in LWCW was significantly higher in NT in the 200 – 300 mm depth compared to MP. Tillage did not influence LI, SC or FRD in WLWC during year 1. There were however significant differences in CC between tillage practices in WLWC rotation. Deep tine resulted in significantly lower flag leaf CC compared to MP. Biomass production (BMP) was significantly higher in MP compared to NT for WLWC. IRM was significantly higher in DT compared to MP and NT for WLWC. During year 2 no significant differences were recorded for the effect of tillage on LI, CC, BMP and FRM in LWCW. DT however resulted in a significantly higher IRM compared to MP in LWCW. Tillage did not influence FRM in WLWC during year 2. MP and NT however resulted in significantly higher LI compared to DT in the beginning of the season. Leaf CC was significantly higher in MP, 60 and 120 days after planting compared to NT and DT in WLWC. MP also significantly increased BMP in WLWC compared to NT. The IRM for WLWC increased significantly with DT compared to NT. During year 2 no significant differences were recorded for the effect of tillage on BMP in McWMcW. NT had a significantly higher IRM compared to MP for WMcWMc. The final root mass also showed significant differences in the 100 - 200 mm range. DT significantly increased FRM in this range compared to MP.
During year 1 no significant differences between tillage practices were recorded for seedling emergence and survival rates, ear-bearing tillers per square metre (ear-bearing tillers per m2), spikelets per ear, kernels per ear, thousand kernel mass (TKM), grain yield, grain protein and hectolitre mass (hl). Significant differences were recorded between crop rotations as grain protein content of wheat was higher in McWMcW compared to LWCW. Canola seedling emergence and survival, number of pods, seeds per pod, seed yield and TKM was not influenced by tillage in year 1. No-till (NT) however resulted in significantly higher seed oil content than MP. During year 2 wheat spikelets per ear and kernels per ear were not influenced by tillage. No-till however, resulted in significantly higher wheat seedling emergence and survival rates, ear-bearing tillers per m2, grain yield, grain mass, TKM and Hl compared to MP. In comparison with DT, NT significantly increased the amount of ear-bearing tillers per m2 and grain yield. Mouldboard plough and DT however showed a significant increase in protein content compared to NT. There were no significant differences for the effect of tillage on canola seedling emergence and survival, seeds per pod, seed yield, TKM and percentage oil for year 2. DT and MP however had a significantly higher number of pods per plant compared to NT. Medic biomass production was not influenced by tillage during year 2. Strategic tillage resulted in positive and negative effects regarding reproductive components.
Soil samples taken before tillage treatments were applied showed that there were no significant differences in the number of weeds (Lolium multiflorum, Polygonum aviculare and Vicia spp) that germinated between subplots. Data recorded in the field during year 1 showed a significant reduction in the number of Lolium multiflorum with a strategic MP tillage compared to NT. During year 2 the number of seeds that germinated under shade net showed that MP tillage the previous year significantly reduced the number of Lolium multiflorum seedlings. These results were also recorded in the field study which showed a reduction in the number of seeds that germinated the second year after tillage. During year 2, shade net trials showed that MP significantly reduced the number of Polygonum aviculare compared to DT and NT. Tillage had no significant effect on the number of Vicia spp and on the number of broadleaf weed species recorded during year 1 and year 2. MP however, reduced the number of unidentifiable weed species during year 1 and year 2. Crop rotation with canola and medic reduced the number of weed plants recorded throughout this study.
The conclusion is that a strategic tillage operation can have positive effects on crop production, but the tillage operation has to be economically viable and improve yield without damaging the environment.||en_ZA