Universität zu Köln

Chen, Hao (2024). Reduction of agricultural soil N losses during the winter season by straw amendments, nitrification inhibitor and by intercropping. PhD thesis, Universität zu Köln.

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Abstract

Nitrogen (N) is a fundamental element for plant and crop growth, but soil N losses may cause low crop N use efficiency and reduced biomass. Moreover, soil N losses such as nitrous oxide (N2O) emissions and nitrate leaching are causing environmental problems. In order to reduce N losses soil amendment with straw and the application of nitrification inhibitors are used in agriculture. Straw amendment stimulates the microbial uptake of N for stoichiometric reasons, thus reducing N losses form soil. However, significant parts of N may still remain sequestered in soil microbial biomass and cause N shortage of crops if N is not released in time, studies on long-term effects of straw incorporation and its effects on the performance subsequent crops are quite rare. Besides of soil amendment, a good crop management (i.e. intercropping and crop rotation) can also reduce soil N losses and improve crop N use efficiency. Different from intercropping, the effects of crop rotation are mediated through indirect feedback interactions known as plant-soil feedback (PSF) effects, the preceding plant affects the soil abiotic and biotic components that influence the succeeding plant generation. However, little is known about the ecological interactions and how the underlying mechanisms can also be utilized to enhance cropping systems productivity. The research of combining spatio-temporal diversity (intercropping together with crop rotation) in cropping systems is needed. Therefore, this thesis aimed to evaluate the effects of crop management (i.e. intercropping) and soil amendments application (i.e. application of straw and nitrification inhibitor) on crop growth, and the effects of soil amendments application on soil N losses under temperature variation (i.e. cooling-warming and freezing-thawing cycling). A mesocosm experiment was designed in chapter 1, to reproduce the dynamics of soil N cycling before and after crop growth, and simulate winter temperature fluctuations under three different N fertilisation rates, incorporate with straw and nitrification inhibitor (NI). Straw addition promoted microbial fixation of N, thereby reducing soil N leaching and total N losses. NI was effective in reducing soil N2O emissions and mitigate N2O emissions caused by straw application. Soil cooling-warming enhanced ammonification and straw induced microbial fixation of N was released at the end of the experiment. But re-mineralization in no-N and low-N rates was insufficient at critical times of early barley growth, concurrently, barley biomass was decreased at both no-N and low-N fertilization rates. Therefore, adequate N fertilisation, combined with straw application, is essential to regulate the timely re-mineralisation of N for succeeding crops. A mesocosm experiment that simulated the seasonal temperature variation was conducted in chapter 2, to investigate the effects of wheat straw amendment NI and temperature variation (both freezing-thawing and cooling-warming) on N losses from soil as N2O and leachate with and without N fertilization. We observed straw addition reduced N leaching and total N losses, but increased the N2O emission by denitrification in high N fertilizer levels. NI effectively reduced N2O emission after fertilization. Cooling-warming strongly induced N mineralization and caused N2O emission peak even in the absence of freezing-thawing, while freezing-thawing increased the N2O emission furtherly. In chapter 3, we set up a field trial consisting of an intercropping phase followed by a rotation phase. In the intercropping phase, maize, faba beans and lupins were grown as monocultures or mixtures of the two as intercrops. In the subsequent rotation phase, barley monocultures were grown to test the plant-soil feedback (PSF) effects of the intercropping phase. The results were both good intercropping species combinations (maize and broad bean) and inefficient intercropping combinations (lupin with other crops). In addition, the intercropping phase altered soil mineral N content, but the feedback effect of intercropping had no impact on barley biomass. Although intercropping had no significant PSF effects in this experiment, PSF effects could be important for crops on soils with low fertiliser application or poor fertility. In conclusion, straw addition significantly reduced soil N losses, NI addition counterbalanced the increased N2O emissions due to straw amendment at high N fertilization, a great challenge of straw application is the timing of N-release for the following crop. Positive effects of intercropping on above-ground biomass are species specific, but soil legacies from the intercropping phase had no effect on soil microbial parameters and barley above-ground biomass in the rotation phase. In order to maximise crop yield and benefit the environment, management practices like intercropping, crop rotation, and the use of soil amendments like NI, straw should be carefully chosen for adoption based on the unique characteristics of the arable land as well as the costs and labour inputs.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Chen, Hao hchen10@smail.uni-koeln.de UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-730687
Date:	2024
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Zoologisches Institut
Subjects:	Agriculture
Uncontrolled Keywords:	Keywords Language N immobilization UNSPECIFIED Nitrogen use efficiency UNSPECIFIED Temperature effect UNSPECIFIED Soil legacies UNSPECIFIED Plant-soil feedback effects UNSPECIFIED Microbial biomass UNSPECIFIED N losses UNSPECIFIED
Date of oral exam:	1 May 2024
Referee:	Name Academic Title Michael, Bonkowski Prof. Dr. Eric von, Elert Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/73068