Effects of nitrogen fertilizer application rate and time to first harvest on leaf area index; leaf nitrate content and yield of irrigated leaf rape (Brassica napus L. var. Giant)

In Zimbabwe, smallholder cultivation of leaf rape is of considerable importance due to the increasing demand for the leaf vegetable from the rapidly increasing urban populations. A two-season field trial was conducted in the Agricultural Practice Experimental Plots of the Midlands State University in central Zimbabwe. The objective of the study was to establish selected biometric responses of leaf rape to N fertilizer rates and time to first harvesting. Increasing the rate of N fertilizer application considerably improves the yield of fresh rape leaf; LAI and concentration of leaf nitrate. Delaying rape leaf harvest after N fertilizer side dressing can be used as a strategy to boost rape leaf yield for vegetable markets with high single delivery demand. When harvesting is deliberately delayed after N fertilizer application rape LAI are significantly increased. Delaying the first leaf harvests by 7; 14 and 21 days after N fertilizer side dressing amendments increases the content of nitrate in fresh rape leaves. Fresh rape yield can be more accurately predicted by values of rape LAI. Nitrate concentrations in fresh rape leaf is a poor predictor of rape yield under field conditions.

KANDUNGAN NITRAT DAUN, PERTUMBUHAN, DAN HASIL BIOMASSA SAWI DAN PAKCOY PADA PEMBERIAN PUPUK NITROGEN ANORGANIK DAN KOMPOS AZOLLA SECARA BERIMBANG

[LEAF NITRATE CONTENT, GROWTH, AND BIOMASS YIELD OF GREEN MUSTARD AND CHINESE CABBAGE FOLLOWING BALANCED APPLICATION OF INORGANIC NITROGEN FERTILIZER AND AZOLLA COMPOST]. The aim of this study was to determine the application rate of Azolla compost, either alone or combined with inorganic N fertilizers, to produce high biomass of mustard greens and Chinese cabbage with low leaf nitrate content. The pot experiments were carried out at the Research Plot of the Faculty of Agriculture located in Bengkulu University Campus from December 2019 to January 2020 with five treatments arranged in a completely randomized design with five replications. The treatments were 100% IF or IF100 (42.0 mg N/kg soil), 100% AC or AC100 (4000 mg/kg soil), IF75 (31.0 mg N/kg soil) + AC25 (1000 mg/kg soil), IF50 (21.0 mg/kg soil) + AC50 (2000 mg/kg soil), and IF25 (10.5 mg/kg soil) +AC75 (3000 mg/kg soil). The results showed that partial replacement of IF with AC (IF75 +AC25) produced plant growth and biomass yield similar to IF100 or higher than IF100 and AC100. The treatment produced plant biomass of 9.35 g plant-1 for green mustard and 167.10 g plant-1 for pakcoy, 32% and 35% higher than AC100 treatment respectively. The leaf nitrate content was 1080 - 2760 mg kg-1 for green mustard and 2310 - 2820 mg kg-1for Chinese cabbage, lower than the maximum limit of safe nitrate for consumption which was set at 3100 mg kg-1. Overall, compared with their sole applications, the partial substitution of inorganic N fertilizer with Azolla compost represents the most effective practice to promote the biomass yield of low-nitrate green mustard and Chinese cabbage.

Constitutive activation of nitrate reductase in tobacco alters flowering time and plant biomass

Pyridine alkaloids produced in tobacco can react with nitrosating agents such as nitrite to form tobacco-specific nitrosamines (TSNA), which are among the most notable toxicants present in tobacco smoke. The market type known as burley tobacco is particularly susceptible to TSNA formation because its corresponding cultivars exhibit a nitrogen-use-deficiency phenotype which results in high accumulation of nitrate, which, in turn, is converted to nitrite by leaf surface microbes. We have previously shown that expression of a constitutively activated nitrate reductase (NR) enzyme dramatically decreases leaf nitrate levels in burley tobacco, resulting in substantial TSNA reductions without altering the alkaloid profile. Here, we show that plants expressing a constitutively active NR construct, designated 35S:S523D-NR, display an early-flowering phenotype that is also associated with a substantial reduction in plant biomass. We hypothesized that crossing 35S:S523D-NR tobaccos with burley cultivars that flower later than normal would help mitigate the undesirable early-flowering/reduced-biomass traits while maintaining the desirable low-nitrate/TSNA phenotype. To test this, 35S:S523D-NR plants were crossed with two late-flowering cultivars, NC 775 and NC 645WZ. In both cases, the plant biomass at harvest was restored to levels similar to those in the original cultivar used for transformation while the low-nitrate/TSNA trait was maintained. Interestingly, the mechanism by which yield was restored differed markedly between the two crosses. Biomass restoration in F1 hybrids using NC 645WZ as a parent was associated with delayed flowering, as originally hypothesized. Unexpectedly, however, crosses with NC 775 displayed enhanced biomass despite maintaining the early-flowering trait of the 35S:S523D-NR parent.

Shading Affects Yield, Elemental Composition and Antioxidants of Perennial Wall Rocket Crops Grown from Spring to Summer in Southern Italy

Shading nets have been increasingly drawing research interest, as they allow us to improve the environmental conditions for greenhouse-grown crops. The effects of two shading nets (50% and 79% shading degree), plus an unshaded control, on yield, mineral composition and antioxidants of perennial wall rocket (Diplotaxis tenuifolia L.-D.C.) grown under tunnels in southern Italy were determined. The shading application resulted in a yield decrease, compared to the unshaded control, except for the highest production under 50% shading in July. The highest yield was recorded in the April–May and May–June and the lowest in July. Similar trends were recorded for plant dry weight, leaf number per rosette and mean weight, but the latter showed the highest value under 79% light extinction in July. The rocket leaves were brighter in the summer cycles than in the spring ones. Leaf nitrate was highest in spring and under 79% shading. Potassium, phosphorus, calcium and magnesium showed the highest values in spring and in the unshaded control. The lipophilic antioxidant activity showed the highest values under the 79% shading net in the spring cropping seasons, whereas in July it did not significantly differ from 50% light extinction. The hydrophilic antioxidant activity always attained the highest values in the unshaded control. The unshaded leaves had the highest total phenol accumulation when grown in April–May and the lowest in July. The total ascorbic acid content was always highest in the unshaded control leaves compared to the shading treatments. Fifty percent crop shading is, therefore, an effective sustainable tool for increasing the yield of perennial wall rocket leaves in July, when the light intensity under the plastic tunnel exceeds the plant requirements, also resulting in a mineral composition that is not significantly different from that of the unshaded crops.

Development of Lettuce Plant in Spring and Autumn Period, Effects of Led Lightening on the Quantity of Mineral Substrates and Leaf Nitrate

Aims: This study was performed during early spring and winter period of 2015-2016 by utilizing soilles technique in a non-heated glasshouse that belongs to Gaziosmanpaşa University Faculty of Agriculture. Study Design: Whereas Funly F1 lettuce species was used as vegetal materials, 2:1 ratio cocopeat and perlite mixture was used as cultivation environment. According to the experiment design, experiment coincidence parcels were performed as 3-recurrences. In the experiment, the effects of different colored LED lights (blue, yellow, red, blue + yellow, blue + red, yellow + red, blue + yellow + red) additional to sunlight were examined. Results: SMD strip LEDs with different colors were used as light source. The light practice does not affect on the plant diameter, plant lenght, SÇKM, pH, titered acid, vitamin C and plant nutrient concentrations. Statistically significant difference occured in the yield of spring and winter curly leaf head salad. There was also an increase at 1% importance level in the light practices compared to the control. In the experiment, red and red blue light combinations had an increase of 1% in the curly leaf head salads in the yield rate when it was compared to the control. Whereas the highest total plant head weight was 840 gr/piece in spring practice, and it was 732 gr/piece for the red light practices in winter practice. Compared to the control, the amount of plant leaf nitrate for the light practices resulted in a decrease at 1% importance level in the curly leaf head salad. When the results were compared with the control conditions, the lowest nitrate contents were obtained as 1764.5 mg NO3-kg- in spring practices, 1898.6 NO3-kg- in winter practices. Coclusion: More amount of nitrate was observed on the leaves of curly leaf head salad in winter practice compared to the one in spring. The amount of leaf nitrate decreased in the light practices compared to the control. As a result, the red and blue light practices and their combinations improved the amount of yield and plant growth by reducing nitrate content.

Sulfur effects on sugar content, enzyme activity and seed yield of rapeseed (Brassica napus L.)

A field experiment was conducted in a randomized complete block design with four sulfur levels, S0, S1, S2 and S3, including 0, 12, 24 and 36 kg ha-1 (respectively) along with 115 kg N ha-1, to evaluate the economic yield of the rapeseed variety (Hyola401) in Abandankash in the Central District of Sari County in Northern Iran. Parameters such as leaf nitrate reductase, root nitrate, leaf and root sugars, root peroxidase, leaf catalase, as well as seed yield were recorded. The results of the analysis of variance revealed that there were highly significant differences between characters for the majority of the traits such as leaf and root nitrate, leaf and root sugars, root peroxidase, leaf catalase, and seed yield. Due to significant positive correlations between root nitrate reductase and seed yield, increasing this enzyme in roots by sulfur application would have an accelerating effect on rapeseed seed yield. A highly significant positive correlation determined between leaf sugar content and seed yield (0.75**) indicated that increasing levels of sulfur had a direct effect on leaf sugar content, which had an accelerating effect on the weight of kernel yield. Sulfur application significantly increased seed yield compared to the control (S0 level), and it ranged from 2744 to 3215 kg ha-1 in S0 and S3.

The Impact of Ammonium to Nitrate Ratio on the Growth and Nutritional Status of Kale

The effect of four NH4:NO3 ratios in the nutrient solution (0:100; 25:75; 50:50 and 75:25) on growth and nutrient concentrations of four kale (Brassica oleraceae L. var. acephala) hybrids: ‘CN KAL 1029’, ‘Redbor’, ‘Winnetou’, ‘Reflex’ and one indigenous cultivar: ‘Ntopia Mytilinis’ was investigated. In the first four weeks of cultivation none of the NH4/NO3 ratios applied induced adverse effects on most growth characteristics determined whereas plants grown with 75% NH4-N accumulated higher leaf N, P, K, Fe, Mn, Zn and Cu concentrations. After an eight week period, plants under 75% NH4-N showed significant reductions in many growth parameters suggesting a probable preference of kale plants grown for a prolonged period towards either a complete exclusion of NH4 from the nutrient solution or a 25:75 or a 50:50 NH4/NO3 ratio. Among the genotypes tested, ‘Ntopia Mytilinis’ produced the greatest yield with the lowest leaf nitrate accumulation. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********