Physical and chemical optimisation of the seedball technology addressing pearl millet under Sahelian conditions

This study deals with the development of the seedball technology in particular for dry sowing under Sahelian conditions and pearl millet as crop. At first, our participatory evaluation in Senegal showed that (i) local materials needed for seedball production are locally available, (ii) the technology conforms to the existing management systems in the Sahel, and (iii) socio-economic conditions do not hinder seedball adoption. Afterwards, seedball was mechanically and chemically optimised. Pearl millet seedlings derived from the seedball variants were grown and compared to the control under greenhouse conditions. Our results showed that the combination of 80 g sand + 50 g loam + 25 ml water is the standard seedball dough, which produces about ten 2 cm diameter-sized seedballs. Either 1 g NPK fertiliser or 3 g wood ash can be added as nutrient additive to enhance early biomass of pearl millet seedlings. Ammonium fertiliser, urea and gum arabic as seedball components hampered seedlings emergence. Seedball + 3 g wood ash and seedball + 1 g NPK-treatments enhanced shoot biomass by 60 % and 75 %, root biomass by 36 % and 94 %, and root length density by 14 % and 28 %, respectively, relative to the control. Shoot nutrient content was not greatly influenced by treatment. However, multiplying biomass yield with nutrient content indicates that nutrient extraction was higher in nutrient-amended seedballs. On-station field tests in Senegal showed over 95 % emergence under real Sahelian conditions. Since early seedlings enhancement is decisive for pearl millet panicle yield under the Sahelian conditions, on-farm trials in the Sahel are recommended

Saatkugeln als Managementoption zur Verbesserung des Auflaufverhaltens von Perlhirse (Pennisetum glaucum) auf sandigen Böden im Sahel

Für den Perlhirseanbau im Sahel sind die frühen Vegetationsstadien von entscheidender Bedeutung. Die Saatkugeltechnologie kann das Auflaufverhalten und die Biomasseentwicklung in dieser Zeitspanne durch Nährstoffadditive (Holzasche, Mineraldünger) verbessern

Modelling Soluble Solids Content Accumulation in ‘Braeburn’ Apples

Optical sensor data can be used to determine changes in anthocyanins, chlorophyll and soluble solids content (SSC) in apple production. In this study, visible and near-infrared spectra (729 to 975 nm) were transformed to SSC values by advanced multivariate calibration models i.e., partial least square regression (PLSR) in order to test the substitution of destructive chemical analyses through non-destructive optical measurements. Spectral field scans were carried out from 2016 to 2018 on marked ‘Braeburn’ apples in Southwest Germany. The study combines an in-depth statistical analyses of longitudinal SSC values with horticultural knowledge to set guidelines for further applied use of SSC predictions in the orchard to gain insights into apple carbohydrate physiology. The PLSR models were investigated with respect to sample size, seasonal variation, laboratory errors and the explanatory power of PLSR models when applied to independent samples. As a result of Monte Carlo simulations, PLSR modelled SSC only depended to a minor extent on the absolute number and accuracy of the wet chemistry laboratory calibration measurements. The comparison between non-destructive SSC determinations in the orchard with standard destructive lab testing at harvest on an independent sample showed mean differences of 0.5% SSC over all study years. SSC modelling with longitudinal linear mixed-effect models linked high crop loads to lower SSC values at harvest and higher SSC values for fruit from the top part of a tree

Modelling Soluble Solids Content Accumulation in ‘Braeburn’ Apples

Optical sensor data can be used to determine changes in anthocyanins, chlorophyll and soluble solids content (SSC) in apple production. In this study, visible and near-infrared spectra (729 to 975 nm) were transformed to SSC values by advanced multivariate calibration models i.e., partial least square regression (PLSR) in order to test the substitution of destructive chemical analyses through non-destructive optical measurements. Spectral field scans were carried out from 2016 to 2018 on marked ‘Braeburn’ apples in Southwest Germany. The study combines an in-depth statistical analyses of longitudinal SSC values with horticultural knowledge to set guidelines for further applied use of SSC predictions in the orchard to gain insights into apple carbohydrate physiology. The PLSR models were investigated with respect to sample size, seasonal variation, laboratory errors and the explanatory power of PLSR models when applied to independent samples. As a result of Monte Carlo simulations, PLSR modelled SSC only depended to a minor extent on the absolute number and accuracy of the wet chemistry laboratory calibration measurements. The comparison between non-destructive SSC determinations in the orchard with standard destructive lab testing at harvest on an independent sample showed mean differences of 0.5% SSC over all study years. SSC modelling with longitudinal linear mixed-effect models linked high crop loads to lower SSC values at harvest and higher SSC values for fruit from the top part of a tree

Determining the optical properties of apple tissue and their dependence on physiological and morphological characteristics during maturation. Part 1: Spatial frequency domain imaging

Relying on the optical properties of apple tissue for nondestructive quality or maturity prediction requires a detailed understanding of the dependence on its structure and ongoing physiological processes. In this study, a multispectral spatial frequency domain imaging (SFDI) setup was used to investigate local changes in the effective scattering coefficient µ's and absorption coefficient µa related to vascular bundles or heterogeneous starch distribution. Weekly measurements during the maturation period for the cultivars `Elstar', `Gala', `Jonagold', and `Braeburn' allowed further study of how different ripening processes affect the scattering and absorption properties. The results show both a characteristic location-dependent decrease of µ's between the cortex and core region of up to 30 % and an additional temporal decrease of up to 35 % during maturation. The absolute changes depended strongly on the respective cultivar. In general, transport structures such as vascular bundles led to a local decrease of µ's in combination with an increased absorption in the spectral regions that can be attributed to water and chlorophyll b. To our knowledge, it was demonstrated for the first time that the presence of starch granules in the cortex of immature apples had a significant effect on µ's, associated with an increase of up to 60 %. Based on the temporal development of µa, the buildup and degradation of important plant pigments in the cortex during the maturation period could be traced. At a wavelength of 656 nm, a decrease in chlorophyll content and at 447 nm, an increase in carotenoid content was observed upon reaching ripeness. Thus, SFDI proved capable of providing deeper insight into the heterogeneous optical properties of apple tissue and linking these properties to physiological variables. Part 2 of this study investigates the observed effects from a theoretical point of view based on a Mie model considering microstructural properties