Doktorandid

Mulla seisundit hinnatakse nii keemiliste, füüsikaliste kui ka bioloogiliste omaduste kaudu. Minu doktoritöö keskendub mullaelustiku meso- ja makrofauna hulka kuuluvatele hooghännalistele ja vihmaussidele kui mullas toimuvate häiringute suhtes tundlikele indikaatorliikidele, kelle arvukuse ja liigilise mitmekesisuse abil on võimalik hinnata mullakvaliteeti.

Vihmaussid mõjutavad mullas toimuvaid protsesse nii vee reguleerimist kui ka toitainete ringlust, mistõttu võib nende arvukust ja liigilist mitmekesisust seostada mulla kvaliteediga. Hooghännalised, kes on head orgaanilise aine lagundajad, osalevad seeläbi samuti toitainete ringluses. Sügavas mullas elavasse ökoloogilisse gruppi kuuluvad hooghännalised on näiteks tundlikud kuivamise suhtes. Bioloogilised indikaatorid võivad olla sobilikud hindamaks põldude majandamisest ja keskkonna- ning kliimamuutustest tingitud mõjusid. Antud doktoritöös keskendutakse Euroopa boreaalsele regioonile ja kliimale.

Doktoritöö eesmärgid on järgmised:

1. Leida ja hinnata mulla funktsioonide ja mullaelustiku (meso- ja makrofauna) vahelisi seoseid, võttes aluseks mullaelustikku sisaldavate projektide alusel koostatud elustikupõhise andmebaasi.

2. Leida põllumajandusmaade mullafunktsioonide põhilised faktorid, mis mõjutavad mulla meso- ja makrofaunat.

3. Leida kaasaegsete põllumajanduspraktikate mõju mullaelustiku funktsioonidele.

4. Modelleerida erinevate mulla bioloogilise mitmekesisuse indikaatorite ja mullaomaduste vahelised seosed, mis on mõjutatud maakasutusest ja ilmastikutingimustest.

5. Modelleerida erinevate kliimamuutuste stsenaariumite mõju mullaselgrootutele (vihmaussidele ja hooghännalistele)

Muldade intensiivne kasutamine põhjustab nende degradeerumist ning vähendab muldade võimet täita oma ökosüsteemiteenuseid. Mulla kvaliteet väljendab mulla suutlikkust täita oma funktsioone, ning seda mõõdetakse hinnates erinevaid füüsikalisi, keemilisi ja bioloogilisi parameetreid, mis üheskoos annavad informatsiooni selle kohta, kuidas muld tervikuna talitleb. Mulla kvaliteedi hindamine on oluline, et toetada muldade kasutamist hõlmavaid poliitilisi otsuseid ning uurida põllumajanduspraktikate jätkusuutlikkust. Agroökosüsteemide mulla kvaliteedi hindamiseks on vajalik leida parameetreid, mis oleksid piisavalt tundlikud erinevate põllumajanduspraktikate suhtes. On leitud, et bioloogilised parameetrid võivad teatud juhtudel olla tundlikumad majandamisest tingitud keskkonnamuutuste suhtes, kuid nende kasutamine mulla kvaliteedi indikaatoritena ei ole leidnud laialdast kasutamist.

Täpsemad uurimiseesmärgid:

- Selgitada välja erineva harimisintentsiivsusega praktikate mõju mulla kvaliteedi füüsikalistele, keemilistele ja bioloogilistele parameetritele

- Viia läbi mulla kvaliteedi kvantitatiivne hindamine Eesti tootmispõldudel

- Analüüsida majandamisviiside mõju mulla bioloogilistele parameetritele

Lühiülevaade: 

Good soil aggregate stability is an essential indicator of high organic matter and high yield. One way of increasing soil aggregate stability is to incorporate in the soil, cover crops as fresh soil organic matter. The fast decomposition of readily accessible fresh organic matter improves microbial activity and has a transient effect on aggregate stability. Also, during their growth cover crops exude root exudates (polysaccharides, lipids, etc.) which serve as an organic matter source for microorganisms. In exchange, microorganisms produce aggregates binding agents. The pathways of the organic matter sources in the soil are complex and still hard to predict. In the experiments in Estonia as well in Latvia and Lithuania the incorporation of cover crops had a negative or no effect on the soil aggregate stability. The reasons for such kind of results are still unknown. Our research project aims to identify the effect of different cover crops on the soil aggregate stability in a sandy loam soil by taking into consideration the effect of such factors as crop residues biochemical composition, soil conditions and soil biological properties.

The main research goals of the project are:

• to study the effect of decomposition rates of different cover crops on the soil aggregate stability;
• to evaluate the effect of plant glucosinolates compounds on the soil microbial activity and soil aggregate stability;
• to study the role of the root exudates exuded by cover crops in soil aggregation and soil aggregate stability;
• to investigate the effect of the soil phosphatase on the soil aggregate stability.

Nitrogen (N) losses from animal manures is associated with not only severe environmental impacts but also fertilizer losses. The gaseous loss of N also reduces the value of animal manure as a fertilizer for crop production. Depending on the storage period, N losses from livestock digestate can account for between 40% - 60% or even more of total N contained in the slurry digestate.

The mitigation of N losses from slurry digestate has become a major focus of research in many countries. Currently, there are few effective technologies to reduce N losses during slurry manure storage and thus development of new options is required. A possibility to reduce and decrease nutrient losses is to add biochar amendment in the organic fertilizers or directly to the soil. Recent studies suggest using biochar amendment to augment the efficiency of organic fertilizers. It creates a higher nutrient retention level, reduces leaching and improves the physical and chemical properties of the soil.

The general objective of our study is to increase the understanding about how to diminish the N losses from organic fertilizer storage and nutrient losses from organic fertilizer application.

The specific research objectives are:

• to identify to what extent biochar could reduce N volatilization from digestate;
• to study the effect of various types of biochar on N losses from digestate during long-term storage;
• to investigate nutrient leaching or losses during vegetation and post-harvest period after the application to the soil of the pre-treated with biochar organic fertilizer.

Kogu maailmas otsitakse lahendusi, millega leevendada kliima soojenemist ja põllumuldade viljakuse vähenemist. Suurt tähelepanu on pälvinud biosüsi, sest see võimaldab atmosfäärist seotud süsinikku kasutada mulla orgaanilise süsiniku sisalduse tõstmiseks. Lisaks on biosöel positiivne mõju tervele reale mulla füüsikalis-keemilistele näitajatele. Kuigi biosütt on viimasel kümnendil uuritud kogu maailmas väga intensiivselt, ei ole siiani päris selge, milline on selle tegelik mõju mullaomadustele. Valdav osa senistest uuringutest on olnud lühiajalised, mistõttu iseloomustavad nende tulemused biosöe mõju ainult mulda viimise järel. Biosöe omadused mullas muutuvad ja samuti võib selle mõju mullaomadustele ajas muutuda, kui pärast biosöe mulda viimist hakkavad selle osakesed mullaprofiilis aja jooksul ühtlasemalt jaotuma.

Seni on biosütt mulda viidud kas puhtal kujul või segatuna mõne orgaanilise väetisega. Ei ole teada, millise efekti annab biosöe lisamine puu- ja põlevkivituhale. Mõlemad tuhad on Eestis tuntud kui lubiväetised. Biosöe lisamine võib nende mõjuspektrit mullale laiendada, seda nii biosöes sisalduva stabiilse süsiniku, toiteelementide kui ka biosöe füüsikaliste näitajate tõttu.

Käesolevas doktoritöös käsitletakse i) biosöe mõju dünaamikat näivleetunud mulla füüsikalis-keemilistele näitajatele 9 aastat kestnud katsest kogutud andmete baasil ja ii)  biosöe mõju  puu- ja põlevkivituha väetusomadustele.

Täpsemalt uuritakse:

• mulla poorsuse, vee- ja katioonide neelamismahutavuse, lasuvustiheduse, agregaatsuse jt näitajate muutumist 9 aasta vältel pärast biosöe laotamist;
• muutusi, mis toimusid mullas biosöe pinnal funktsionaalsete rühmade arvus ja koosseisus;
• biosöe lisandi mõju puu- ja põlevkivituhast toitainete vabanemisele ja taimede poolt omastamisele ning mulla füüsikalis-keemilistele näitajatele.

Soil quality is regulated by the physical, chemical, and biological properties of soil. My doctoral thesis focuses on the meso- and macrofauna of soil biota, particularly earthworms and springtails. These soil biota indicators are sensitive to soil disturbances, making them appropriate for assessing soil quality based on species richness and abundance.

Earthworms affect processes in soil like water regulation and nutrient circulation and springtails are also effective decomposers. However, some springtail species (particularly those that live deep in the soil) are sensitive to drought. These soil biota indicators may be useful for evaluating the effects of agricultural practices, environmental factors and climate change. This doctoral thesis focuses on boreal region in Europe.

Aims:

1. To find out and estimate the selected soil functions and soil biodiversity (meso- and macrofauna) links based on a soil database collected in previous projects.

2. To identify the main factors for soil functions on agricultural fields to soil meso- and macrofauna.

3. To find out how modern agricultural techniques influence the soil functioning biota relationships.

4. To model the relationships between the different soil biodiversity indicators and the soil properties (as affected by management and weather conditions).

5. To model the effect of different climate change scenarios in soil invertebrates (Lumbricidae and Collembola).

The impact of intensive use of soils is causing soil quality degradation, which reduces soils ability to provide ecosystem services. Thus establishing management practices that improve soil quality is of crucial importance to maintain sustainable agriculture. Soil quality expresses soils ability to function, which is measured by integrating and assessing different physical, chemical and biological indicators related to soil processes. Soil quality assessment and monitoring is important to support the policymaking process and to evaluate the sustainability of soil management practices. The soil environment is quite complex and dynamic, which makes the assessment of soil quality rather complicated and emphasizes the need for sensitive indicators that are directly connected to specific functions. It has been found that soil biological indicators can be more sensitive towards management practices and provide an early indication of changes in soil functioning. However, the biological indicators of soil quality are less used for soil quality assessment.

The main research objectives are:

- to investigate the effect of tillage intensity on physical, chemical and biological indicators of soil quality

- to assess soil quality on Estonian production fields

Good soil aggregate stability is an essential indicator of high organic matter and high yield. One way of increasing soil aggregate stability is to incorporate in the soil, cover crops as fresh soil organic matter. The fast decomposition of readily accessible fresh organic matter improves microbial activity and has a transient effect on aggregate stability. Also, during their growth cover crops exude root exudates (polysaccharides, lipids, etc.) which serve as an organic matter source for microorganisms. In exchange, microorganisms produce aggregates binding agents. The pathways of the organic matter sources in the soil are complex and still hard to predict. In the experiments in Estonia as well in Latvia and Lithuania the incorporation of cover crops had a negative or no effect on the soil aggregate stability. The reasons for such kind of results are still unknown. Our research project aims to identify the effect of different cover crops on the soil aggregate stability in a sandy loam soil by taking into consideration the effect of such factors as crop residues biochemical composition, soil conditions and soil biological properties.

The main research goals of the project are:

• to study the effect of decomposition rates of different cover crops on the soil aggregate stability;
• to evaluate the effect of plant glucosinolates compounds on the soil microbial activity and soil aggregate stability;
• to study the role of the root exudates exuded by cover crops in soil aggregation and soil aggregate stability;
• to investigate the effect of the soil phosphatase on the soil aggregate stability.

Nitrogen (N) losses from animal manures is associated with not only severe environmental impacts but also fertilizer losses. The gaseous loss of N also reduces the value of animal manure as a fertilizer for crop production. Depending on the storage period, N losses from livestock digestate can account for between 40% - 60% or even more of total N contained in the slurry digestate.

The mitigation of N losses from slurry digestate has become a major focus of research in many countries. Currently, there are few effective technologies to reduce N losses during slurry manure storage and thus development of new options is required. A possibility to reduce and decrease nutrient losses is to add biochar amendment in the organic fertilizers or directly to the soil. Recent studies suggest using biochar amendment to augment the efficiency of organic fertilizers. It creates a higher nutrient retention level, reduces leaching and improves the physical and chemical properties of the soil.

The general objective of our study is to increase the understanding about how to diminish the N losses from organic fertilizer storage and nutrient losses from organic fertilizer application.

The specific research objectives are:

• to identify to what extent biochar could reduce N volatilization from digestate;
• to study the effect of various types of biochar on N losses from digestate during long-term storage;
• to investigate nutrient leaching or losses during vegetation and post-harvest period after the application to the soil of the pre-treated with biochar organic fertilizer.

Solutions are being sought to mitigate global warming and soil fertility decline around the world. Biochar has received a lot of attention because it makes possible to increase the soil carbon content through the bound carbon from the atmosphere. In addition, biochar has a positive effect on many physico-chemical parameters of soil. Although biochar has been studied very intensively over the last decade, its real impact to the soil properties is still unclear. The majority of previous studies have been short-term, so in their results, the effects of biochar are just after application to the soil characterised. The properties of biochar in the soil change and also the effect of biochar on soil properties may change over time when its particles are gradually distributed more evenly in the soil profile.

Until now, biochar has been used mainly either without or with some organic fertilizers. The effect of biochar on wood and oil shale ash is unknown. In Estonia, both ashes are known as lime fertilizers. The addition of biochar can broaden their spectrum of action on soil, due to the stable carbon and nutrients in the biochar, as well as the physical properties of the biochar.

This dissertation deals with i) the dynamics of the effect of biochar on the physico-chemical parameters of Luvisols on the basis of data collected from a 9-year experiment, and ii) the effect of biochar on the fertilization properties of wood and oil shale ash.

In this study we investigate:

• changes in soil porosity, water and cation exchange capacity, bulk density, aggregation, etc. during the 9 years after biochar application;

• changes in the amount and composition of functional groups on the surface of biochar in the soil;

• the effect of the addition of biochar on the release of nutrients from wood and oil shale ash, uptake by plants, and on the physico-chemical parameters of the soil.

Kerttu Tammik

kerttu.tammik@emu.ee

Supervisors: 

Jordi Escuer Gatius

2021

Kersti Vennik

Diego Sanchez De Cima