On-line NIR-measurement of soil moisture content

Oikein ajoitetulla kylvöllä on merkittävä vaikutus viljasatoon. Kylvöajan määräävinä tekijöinä ovat lämpö ja kosteus. Viljan siemenen optimaaliseen kosteuteen saattamisen todennäköisyyttä, olisi ainakin teoriassa mahdollista parantaa maan kosteuteen perustuvalla kylvösyvyyden säätelyllä. Kylvön aikainen, eli liikkeessä tapahtuva kosteusmittaus, vaatii jatkuvaan mittaukseen soveltuvan mittalaitteiston. Lupaavalta teknologialta maan kosteuden jatkuvaan mittaamiseen vaikuttaa NIR- eli lähi-infrapunaheijastukseen perustuva mittausteknologia, joka ei vaadi kosketusta mitattavaan materiaaliin. Materiaalin kosteuden NIR-mittaukset perustuvat heijastuneen ja absorboituneen säteilyn suhteen mittaukseen, josta kalibroinnin avulla saadaan selville materiaalin kosteus. Tämän työn tavoitteena onkin selvittää soveltuuko Visilab IRMA 7 D NIR-mittalaite ominaisuuksiensa puolesta maan kosteuden jatkuvaan mittaamiseen pelto-olosuhteissa sekä lisäksi pohtia mittalaitteen hyödyntämismahdollisuutta maan jatkuvaan kosteuden mittaukseen perustuvassa automaattisessa kylvösyvyyden säädössä. Tutkimuksen tavoitteen saavuttamiseksi laite kalibroitiin kolmelle eri maalajille. Lisäksi testattiin laitteen soveltuvuutta jatkuviin mittauksiin sisätiloissa stabiileissa olosuhteissa selvittämällä mittalaitteen aiheuttama hajonta, askelvaste sekä mitattavan pinnan kulman vaikutus. Jatkuvien mittausten suorittamiseksi rakennettiin työkone, jonka avulla mittalaitetta kyettiin vetämään traktorin perässä. Lisäksi perustettiin koekenttä, jolla jatkuvia mittauksia suoritettiin. Tulosten perusteella mittalaite on kyllin nopea ja mittalaitteen aiheuttama hajonta on riittävän pieni jatkuviin pelto-olosuhteissa tapahtuviin mittauksiin. Suuri mittausetäisyys mitattavaan materiaaliin ja tästä johtuva mittausalueen suuri valokeila, vaativat laajan ja tuoreen pinnan, jolle ei saisi valua maata mittauksen aikana. Pienempi valokeila ja lyhempi mittausetäisyys antaisivat laitteistolle paremmat hyödyntämismahdollisuudet maan jatkuvassa kosteusmittaussovelluksissa, vähentämällä laitteiston häiriöherkkyyttä. Tutkimuksen tavoitteena oli suorittaa enemmän jatkuvia mittauksia pelto-olosuhteissa, joilla selvitettäisiin laitteen soveltuvuutta maan kosteuden jatkuviin mittaussovelluksiin. Mittauksia ei päästy suorittamaan haluttua määrä johtuen syksyn sateista ja koekentän pellon vettymisestä. Tehdyt mittaukset olivat pääosin laitteiston testaukseen ja kehittämiseen tähtääviä mittauksia.Timing has a significant influence on grain yield. Determining factors for sowing time are moisture and temperature. Automatic sowing depth control would at least theoretically increase the chance for the seed to get sown in optimal moisture. Depth control during sowing requires technology suitable for on-line measurement of soil moisture content. Acquisition of soil moisture by Near Infrared reflectance (NIR) - seems promising for on-line measurements. NIR moisture measurements of a material do not require contact between the NIR-sensor and the measured material. NIR-measurements of material moisture content are based on the relationship between the absorbed and reflected radiation, sent to the material from a light source and measured by the NIR-sensor. The main goals of the study were to determine the suitability of Visilab IRMA 7D-moisuremeter for in field on-line soil moisture measurements and to consider the applicability of the moisture meter for automatic sowing depth control. To achieve the goals of the study the moisture meter was calibrated for three different soil types. Moisture measurements were carried out indoors in stable conditions to determine the dispersion and step response of the moisture meter. Also the impact of the angle between the measured surface on the moisture meter was examined. To achieve the main goal of the study a tractor operated implement was built to carry out the infield on-line moisture measurements of soil moisture content. In addition a test field was established in order to complete the measurements. According to the results of this study the Visilab IRMA 7D-moisture meter is fast enough and the dispersion is small enough for infield on-line soil moisture measurements. Long measuring distance and large beam of light requires a large and fresh area on the measured surface. Any soil should not run over on the area of the light beam during moisture measurements to achieve accurate results. A smaller area beam and shorter measuring distance would provide better potential for usage in infield on-line soil moisture measurements, by reducing sensitivity to external disturbance. The goal of the study was to perform more infield measurements to more specifically determine the suitability of the moisture meter. The measurements were not however performed due to the heavy rainfall during the autumn. The measurements which were carried out aimed more for the development of the implement

Plant residue mulch increases measured and modelled soil moisture content in the effective root zone of maize in semi-arid Kenya

Difficulties in efficient utilization of seasonal precipitation cause limitations in yields and even total crop failure on rainfed farms in semi-arid East Africa. The objective of the present study was to find out if covering the soil with plant residue mulch at a semi-arid site could retain water in the soil between precipitation events and build dry spell resilience by reducing soil water evaporation and increasing infiltration to deeper soil. Covering soil with plant residue mulch was studied at a smallholder farm in semi-arid Kenya by continuously measuring volumetric soil moisture content with soil sensors at multiple depths in bare soil and in maize (Zea mays L.) plant residue mulched soil. A physically based one-dimensional soil moisture model was calibrated and used to estimate the effect of plant residue mulch on soil moisture over a two-year period (multiple growing seasons). The modelled multiyear time series provides an estimate of the effect residue mulches of different thicknesses have on soil moisture over time. The simple soil moisture model was able to estimate soil moisture in the effective root zone of maize. By comparing measured data from mulched and uncovered soil and by model prediction, it was demonstrated that maize residue mulch conserved soil moisture over time in the effective root zone of maize compared to bare soil. During the two-year period mulching increased the total amount of days when measured relative soil moisture (s) exceeded water stress limit of maize (s*) by 24%-46%. Moisture accumulated in the mulched profile, especially in the deeper layers of the effective root zone. Calculations indicated that further increasing mulch thickness (delta(m)) from 1 to 3 cm would have increased the total days when s > s* 59%. Furthermore, increasing delta(m) from 3 to 5 cm would have resulted in 25% increase in total days when s > s*. According to our calculations mulching (delta(m) > 1 cm) could have maintained s > s* throughout a 19 days dry spell that occurred during the measurement period. The demonstrated moisture conserving effect of mulch increases with delta(m), but availability of plant residue may set limits on mulch application rates. The results suggest that maize residue mulching is as an accessible and feasible method for conserving soil moisture in the effective root zone in dryland smallholder systems in East Africa.Peer reviewe

Pulp mill sludges as a solution for reducing the risk of mineral nitrogen leaching from agriculture

Nitrogen (N) from agricultural systems contributes to the eutrophication of waterbodies through leaching. Incorporating organic material with a high carbon-to-nitrogen (C/N) ratio, such as mixed pulp mill sludges (PMSs), into the soil in autumn could reduce the amount of leachable N. This study tested the potential of composted and lime-stabilised mixed PMSs (CPMS and LPMS) in reducing the concentration of mineral N in the soil, and thus the risk of N leaching from arable land in the boreal region using a two-year field experiment. To better understand the mechanisms of the PMSs for influencing mineral N concentration in soil, the impact of PMSs with different quality on the reactions of N in the soil was investigated in a laboratory incubation study. In the field experiment, nitrate-N (NO3--N) concentration was lower with PMSs compared to mineral fertilisation and the control during the first autumn and the following spring after PMS application. The undersowing of Italian ryegrass reduced the NO3--N concentration in the soil during the first autumn. In the incubation experiment, PMSs reduced the soil ammonium-N (NH4+-N) concentration at the beginning of the experiment and the soil NO3--N concentration throughout the experiment compared to a mineral fertiliser treatment and an organic fertiliser. Increased soil respiration in PMS-treated soils indicated increase in microbial activity, and thus immobilisation of soil NO3--N and NH4+-N due to PMSs addition. These results suggest that PMSs have the potential to reduce N leaching from agricultural soils. However, the immobilisation of N must be considered when planning the nutrient requirements of the following crops

Comparing plastic foils for dew collection : Preparatory laboratory-scale method and field experiment in Kenya

Passive dew collection could be a viable option as a source of irrigation water in arid areas. The plastic foil acting as a condensing surface plays a key role in the passive dew collection regime. A laboratory method for comparing various plastic foils for dew collection was prepared and tested. The focus was on creating a method for measuring the attributes affecting dew condensation and the flow of dew droplets on the measured surface. A low-density polyethylene foil designed for dew collection, white polyethylene plastic, black polyethylene plastic, and white polyvinyl chloride plastic were used as the test plastics. The laboratory dew yields were compared with model calculations. In addition, field trials were conducted in arid conditions in Maktau, Kenya, to compare with the laboratory measurement. Results from the hardware model tests were not reflected in the results obtained from the field conditions. The laboratory tests showed that the dew-harvesting quality of plastic foils is difficult to evaluate using the laboratory test rig. A more comprehensive evaluation regime requires tests performed in field conditions or further development of the test rig used here. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.Peer reviewe

An Attempt to Utilize a Regional Dew Formation Model in Kenya

Model evaluation against experimental data is an important step towards accurate model predictions and simulations. Here, we evaluated an energy-balance model to predict dew formation occurrence and estimate its amount for East-African arid-climate conditions against 13 months of experimental dew harvesting data in Maktau, Kenya. The model was capable of predicting the dew formation occurrence effectively. However, it overestimated the harvestable dew amount by about a ratio of 1.7. As such, a factor of 0.6 was applied for a long-term period (1979–2018) to investigate the spatial and temporal variation of the dew formation in Kenya. The annual average of dew occurrence in Kenya was ~130 days with dew yield > 0.1 L/m2/day. The dew formation showed a seasonal cycle with the maximum yield in winter and minimum in summer. Three major dew formation zones were identified after cluster analysis: arid and semi-arid regions; mountain regions; and coastal regions. The average daily and yearly maximum dew yield were 0.05 and 18; 0.9 and 25; and 0.15 and 40 L/m2/day; respectively. A precise prediction of dew occurrence and dew yield is very challenging due to inherent limitations in numerical models and meteorological input parameters

An Attempt to Utilize a Regional Dew Formation Model in Kenya

Model evaluation against experimental data is an important step towards accurate model predictions and simulations. Here, we evaluated an energy-balance model to predict dew formation occurrence and estimate its amount for East-African arid-climate conditions against 13 months of experimental dew harvesting data in Maktau, Kenya. The model was capable of predicting the dew formation occurrence effectively. However, it overestimated the harvestable dew amount by about a ratio of 1.7. As such, a factor of 0.6 was applied for a long-term period (1979–2018) to investigate the spatial and temporal variation of the dew formation in Kenya. The annual average of dew occurrence in Kenya was ~130 days with dew yield > 0.1 L/m2/day. The dew formation showed a seasonal cycle with the maximum yield in winter and minimum in summer. Three major dew formation zones were identified after cluster analysis: arid and semi-arid regions; mountain regions; and coastal regions. The average daily and yearly maximum dew yield were 0.05 and 18; 0.9 and 25; and 0.15 and 40 L/m2/day; respectively. A precise prediction of dew occurrence and dew yield is very challenging due to inherent limitations in numerical models and meteorological input parameters

Dew Collection and Mulching as Measures to Improve Water Balance in Dryland Agriculture

Water scarcity is globally a key reason for crop yield losses. Difficulties in efficient utilization of the total available precipitation cause yield limitations and even total crop failure at rainfed dryland farms. This study assessed two potentially available measures to improve the water balance of dryland agriculture; water recovery through passive dew collection and soil mulching with plant residue. Dew collection field experiments were conducted to evaluate the effectiveness of various plastic materials in dew collection in dryland conditions. The planar dew collectors were of the standard type: a 1 m2 surface tilted at 30◦ in respect to the horizontal. Dew yields were measured daily over a one-year period. The condensing surface temperatures and the meteorological conditions were monitored continuously, to calculate potential dew output. A laboratory method was prepared and tested for evaluating the attributes affecting dew condensation and droplet flow. The condensing surfaces were cooled below dewpoint by utilizing Peltier elements in controlled conditions. Dew yields measured in laboratory conditions were compared with calculated dew outputs, and with dew yields measured in field conditions. Dew occurred throughout the year, even through the dry seasons, and may be considered a small but reliable source of water. Annual dew yields were < 8% of the annual precipitation (322 mm). No significant differences were found between the tested materials. Clear skies, calm winds (0.5–2.5 m s-1), and conditions with dew point close to air temperature (Tdew ≈ Tair) favor dew condensation. Placement in the field affects the airflow characteristics at the condensing surfaces and ultimately the collected dew quantities, thus attention should be paid to the placement of the dew collectors in the field. Based on our results, a more comprehensive laboratory evaluation regime, with specific design and measurements of the airflow characteristics is needed to draw valid conclusions on the differences between the plastic foils. Mulching with plant residue was studied by measuring soil volumetric water content in vertical profiles in bare and plant residue-covered soil during a 100-day period. A one-dimensional model based on Richard’s equation was used to predict the effect of mulch over a two-year period. Compared with bare soil, mulching prolonged the time when continuously measured soil moisture content exceeded the water stress limit of maize. The predicted water-conserving effect increased with mulch thickness. However, plant residue mulch degrades naturally and the availability and competitive uses of plant residues may limit the thickness of the mulch layer. A mulch layer with a thickness of > 1 cm brought clear improvements to the soil moisture conditions and resilience against dry spells compared with bare soil. The presented models were capable of estimating the cumulative dew condensation and soil moisture behavior satisfactorily over time. For further development of the dew condensation model, more specific airflow measurements are needed for calculating the mass transfer for more accurate predictions of nightly dew quantities. This study touched upon the combined effect of irrigation with dew water and mulching on by using modeling to predict the effects on soil moisture. The results indicated that mulching improves the usability of irrigational water recovered from dew by reducing evaporation. The effect increases with layer thickness. Future research steps could include the quantification of the presented water-conserving measures on actual crop yields, especially the combined effect.Vedenpuute on maailmanlaajuisesti yksi merkittävimmistä satoa rajoittavista tekijöistä. Useilla kuivilla viljelyalueilla esiintyy haasteita vähäisen ja epäsäännöllisen sadannan hyödyntämisessä, josta seuraa jopa täysimittaisia sadonmenetyksiä. Tässä tutkimuksessa arvioitiin kahta keinoa kuivien alueiden maatalouden vesitalouden parantamiseksi; passiivista aamukasteen keräämistä kasteluvedeksi sekä maan kattamista kasvijätteellä, haihdunnan hillitsemiseksi. Kenttäkokeet suoritettiin kuivalla alueella Keniassa. Muovimateriaalien soveltuvuutta kasteen keräämiseen arvioitiin kenttäkokein. Kenttäkokeissa käytettiin standardityyppisiä 30° kulmaan kallistettuja tasomaisia 1 m2 kasteenkerääjiä. Kertyneitä kastemääriä mitattiin päivittäin vuoden ajan. Lisäksi kasteentiivistymispinnan lämpötilaa sekä sääparametreja mitattiin jatkuvatoimisesti. Mittaustuloksia hyödynnettiin potentiaalisten kastemäärien mallituksessa. Muovien kasteenkeräysominaisuuksien tutkimiseksi rakennettiin laboratoriomenetelmä, jonka soveltuvuutta ominaisuuksien arvioimiseen selvitettiin. Kastetta tiivistävät pinnat jäähdytettiin Peltier-elementeillä kontrolloiduissa olosuhteissa alle kastepisteen. Laboratorio-olosuhteissa mitattuja kastemääriä verrattiin mallitettuihin kastemääriin, sekä kenttäkokeissa mitattuihin kastemääriin. Kenttäkokeissa kastetta tiivistyi ympäri vuoden, myös kuivien kausien aikana. Aamukaste todettiin pieneksi, mutta luotettavaksi vedenlähteeksi. Vuoden yhteenlasketut kastemäärät olivat < 8% kokonaissadannasta (322 mm). Kaikki tutkitut materiaalit soveltuivat kasteen keräämisen. Materiaalien välillä ei esiintynyt merkittäviä eroja. Kastetta tiivistyi parhaiten kun taivas oli pilvetön, tuuli 0.5–2.5 m s-1 ja ilman lämpötila lähellä kastepistettä. Kenttäkokeissa kasteenkerjääjän sijainnin havaittiin vaikuttavan merkittävästi ilmavirtauksiin ja siten kastekertymään. Esitetty laboratoriomenetelmä vaatii edelleen kehittämistä. Tarkempia mittaustuloksia vaaditaan luotettavien johtopäätösten vetämiseksi. Etenkin ilmavirtaa kasteentiivistymispintojen läheisyydessä tulisi kontrolloida ja mitata tarkemmin. Maan kattamista veden säästämiseksi tutkittiin 100 päivän ajan mittaamalla sääparametreja sekä maan kosteutta eri syvyyksissä kasvijätteellä katetussa ja paljaassa maassa. Katteen vaikutusta arvioitiin edelleen kahden vuoden tarkasteluajanjakson ajan, yksiulotteisella Richardin yhtälöön perustuvalla maankosteusmallilla. Mitattujen ja mallitettujen tulosten mukaan, maan kattaminen hidasti maan kuivumista. Paksumpi katekerros hidastaa kuivumista tehokkaammin, mutta kasvijätteen saatavuutta saattavat rajoittaa muut käyttötarkoitukset, esim. polttoaineena keittiössä tai eläinten rehuna. Tulosten mukaan jo > 1 cm paksuisen katekerroksen havaittiin selvästi parantavan maan kosteusolosuhteita ja resilienssiä sadekausien lyhyitä kuivia jaksoja vastaan. Tutkimuksessa käytetyt teoreettiset mallit ennustivat tyydyttävällä tarkkuudella kasteen kertymistä sekä maan kosteuden käyttäytymistä. Kasteenkertymistä ennustavan mallin lyhyen aikavälin tarkkuuden parantamiseksi tulisi kasteen tiivistymiseen vaikuttavia ilmavirtoja mitata tarkemmin. Tutkimuksessa sivuttiin kasteesta kerätyllä vedellä kastelun ja maan kattamisen yhteisvaikutusta maan kosteuspitoisuuteen mallittamalla. Tulosten perusteella maan kattaminen vähentää haihduntaa, siten parantaen kasteveden hyötysuhdetta. Katekerroksen paksuuden kasvattaminen parantaa hyötysuhdetta. Tulevissa tutkimuksissa olisi hyvä kartoittaa näiden toimien vaikutusta kasvien kasvuun, etenkin niiden yhteisvaikutusta