4. Nitrogen in the Environment: Mineralization — Immobilization

Nitrogen exists in many forms in the soil and is essential for plant growth and development. Most of the nitrogen found in the soil is in numerous different organic forms. However, plants are unable to use organic forms of nitrogen. Normal, rather complex processes in the soil convert nitrogen from organic forms into ammonium.

Figure 1 Mineralization and immobilization processes

What affects mineralization and immobilization?

Decaying plant material, humus and/or organic matter in the soil are important sources of nitrogen. How much plant residue or organic matter are in the soil, and the types present, can affect the types of nitrogen conversion processes that take place. For example, the presence of a high amount of wheat straw or corn stalks in the soil will result in immobilization processes taking place. Immobilization results in plant usable forms of nitrogen in the soil becoming unavailable for subsequent crop growth. This nitrogen is used by microorganisms in the decomposition process of wheat straw or corn stalks. Once the wheat straw or corn stalks have become highly decayed, immobilization stops and mineralization starts. That is, plant usable forms of nitrogen such as ammonium become available again. Immobilization processes generally do not take place when a legume crop, such as alfalfa or white clover, is plowed under. Mineralization will likely be the dominant process.

Conversion processes of nitrogen to different forms are all accomplished by various groups and types of microorganisms found in the soil. Factors that affect microorganisms, such as temperature, oxygen supply and moisture, can affect the degree to which nitrogen conversions take place.

Impact on water quality

Both immobilization and mineralization processes can have a direct impact on water quality. Immobilization can result in a reduction of inorganic forms of nitrogen, including nitrate. However, this reduction in nitrate is generally temporary.

Mineralization results in the production of ammonium (NH⁺). Under favorable conditions, ammonium is further converted by microorganisms to nitrate. Buildup of nitrates in soil followed by heavy rains can move plant available nitrate below the root zone. Nitrate is a form of nitrogen that is highly mobile and easily moves with water.

Whether nitrates continue to move downward and into groundwater depends on underlying soil and/or bedrock conditions as well as depth to groundwater. If depth to groundwater is shallow and the underlying soil is sandy, the potential for nitrates to enter groundwater is relatively high. However, if depth to groundwater is deep and the underlying soil is heavy clay, groundwater contamination from nitrates is not likely.

5. Future Challenges

Soil chemistry has developed into an important and complex scientific discipline over the past two centuries. Beginning with J. Thomas Way’s simple base exchange work, studies on ion exchange, soil acidity/alkalinity, retention of ions by soils, clay mineralogy and chemistry of oxides and hydrous oxides have become the focal points of soil chemists’ research for decades. These subjects have evolved individually to be so extraordinarily complex and challenging that books and monographs have been and continue to be written on these topics. Up to the late 1960’s soil chemistry dealt mostly with understanding chemical reactions to improve crop productivity. The present research focus is now directed predominantly toward environmental soil research. For example, in the early 1970’s, soil chemists were among the first scientists to characterize the makeup of agricultural, industrial, and urban wastes. Soil chemists found that much of these wastes were comprised of both inorganic (such as soil material) and organic chemical substances.

Our future depends on conducting cutting-edge research elucidating the chemical behavior of soil-related substances at the molecular and macroscopic levels. Such work will improve our ability to make accurate predictions regarding their transport and availability in the environment. This need drives soil chemists to creatively employ state-of-the-art spectroscopy as well as the vast array of new molecular-level technologies continuing to be developed. Our particular challenge as soil chemists is to couple these technologies with vision and computational skill, allowing us to make great strides in unraveling problems that would otherwise remain unresolved. As soil chemists, we should look beyond our own field of science, exploring more of the basic principles of chemistry, organic chemistry, and biochemistry, to improve our imagination and capacity to attain great advancements in our science.

СОДЕРЖАНИЕ

UNIT I AGRONOMY…………………………………………………. Text 1 Agronomist career outlook…………………………………. Text 2 Organic farming…………………………………………….. Text 3 Sustainable agriculture……………………………………… Text 4 What are crops……………………………………………… UNIT II AGRONOMY………………………………………………... Text 1 Changing climate changes soils…………………………….. Text 2 Mighty river, mighty filter………………………………….. Text 3 Potatoes wild with calcium…………………………………. Text 4 Not your grandfather’s cotton ……………………………… UNIT III PLANT PROTECTION……………………………………... Text1 What is plant protection and why it is so important? ……… Text 2 The process of plant protection……………………………. Text 3 The main disciplines involved in plant protection………… Text 4 The Aims of IAPPS………………………………………… UNIT IV INTEGRATED PLANT PROTECTION…………………… Text 1 Competence area within integrated plant protection. Interdisciplinary strategy…………………………………………… Text 2 Competence area within integrated plant protection (continuation). Deep knowledge. Applied research……………….. Text 3 About IPPC…………………………………………………. Text 4 General Principles Integrated Plant Protection…………….. UNIT V HORTICULTURE…………………………………………… Text 1 Chili’ (Pyrus bretschneideri Rehd.) pear fruit…………….. Text 2 Apples………………………………………………………. Text 3 Evaluation of ‘Sun Protect’ in protecting apples (Malus × domestica Borkh.) against sunburn………………………………… Text 4 A screening test for the determination of cut flower longevity and ethylene sensitivity of carnation……………………. UNIT VI HORTICULTURE…………………………………………... Text 1 Evaluation of dormancy break in some selected peach (Prunus persica) cultivars………………………………………….. Text 2 Testing the winter hardiness of selected chrysanthemum cultivars of Multiflora type………………………………………… Text 3 Effects of garlic genotype on cloves formation under in vitro conditions……………………………………………………... Text 4 Timer versus moisture sensor-based irrigation control of soilless lettuce: Effects on yield, quality and water use efficiency… UNIT VII AGROECOLOGY………………………………………….. Text1 Agroecology………………………………………………… Text 2 The potential of agroecology to combat hunger in the developing world…………………………………………………… Text 3 Agroecology and the design of climate change-resilient farming systems…………………………………………………….. Text 4 The effects of climate change on agricultural production…………………………………………………………... UNIT VIII SOIL SCIENCE……………………………………………. Text 1Soil chemistry……………………………………………………. Text 2 Soil fertility (i) ……………………………………………... Text 3 Soil fertility (ii) …………………………………………….. Text 4A soil horizon………………………………………………... EXERCISES…………………………………………………………… SUPPLEMENTARY READING………………………………………

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