**Preface to "Site-Specific Nutrient Management"**

The natural milieu of food production is a field that has to being treated as a base production unit. The production potential of the field depends not only on soil geological origin and the natural fertility level but also on its managemen<sup>t</sup> history. Effective crop production is based on a farmer's extensive knowledge and skills to protect cropped plants against stresses. Most are of environmental origin, such as drought. The sustainable exploitation of soil productivity depends on those soil characteristics that are crucial for the effective managemen<sup>t</sup> of water and nitrogen. The production effect of these two basic production factors, in fact, depends on the status of other, secondary factors. A farmer's knowledge is necessary, first, for their recognition, and second, for developing and implementing measures for their amelioration.

The evaluation of field production level requires thorough recognition of the reasons for its variability. An insight into the soil profile, as the first group of variabilities, cannot be limited to topsoil, as is the case in current agro-chemical diagnostic procedures. An effective managemen<sup>t</sup> of soil resources requires data on soil characteristics in the entire rooted soil zone. The subsoil cannot be treated as a black box. Temporal variability is an inherent property of crop plants during the growing season. The proper development of yield depends on a synchronization of crop plant requirements for water, nitrogen, and their supply from soil. However, those nutrients that are responsive to water and nitrogen uptake and utilization by plants throughout the growing season cannot be neglected. It is also impossible to achieve the production effect, i.e., yield, without taking into account the spatial variability of yielding factors within a field during critical stages of yield component development. The fourth type of variability affecting field productivity is defined by cropping sequence. Effective managemen<sup>t</sup> of soil fertility should be always oriented towards a crop within a particular crop rotation with the highest sensitivity to the current status of soil fertility.

A sound managemen<sup>t</sup> approach to soil fertility is to ameliorate those production factors that are correctable to a level, maintaining maximum water and nitrogen efficiency. Any attempt by farmers that aims to fulfill this target results in an amelioration of the nitrogen gap. This is the only way to reach the twin objectives of the sustainable agriculture, i.e., yield increase, concomitant with the decreased pressure of reactive nitrogen compounds on the environment.

The effective recognition of variability in production factors and their impact on the efficiency of water and nitrogen requires the use of a broad range of diagnostic tools. Reliable diagnosis of the present soil fertility status cannot, however, be conducted successfully without classic soil sampling, and time-consuming soil and agrochemical analyses. Remote-sensing techniques provide a source of data on the dynamics of crop biomass and nitrogen content during the growing season. Spectral data form the basis of quick correction of a crop nutritional status within the growing season.

This book is addressed to four groups of potential readers, at least. The first are farmers who need practical knowledge of how to recognize and create a hierarchy of factors that limit the efficiency of their applied production measures. They also need good advisory support to develop the skills that are necessary to ameliorate the factors that limit soil productivity. Second, the multifactorial level of the evaluation of production factors, as presented in this book, can be helpful for researchers within the field of agronomy. The third group are those who need a broad knowledge of and who are now or will be involved in the agriculture sector. The fourth group are environmentalists. Any action oriented towards environmental protection and addressing correction in current agricultural practices cannot be successful without comprehensive knowledge of agro-ecosystem functioning.

The authors involved in the preparation of the papers included in this issue are specialists in agronomy, soil and plant diagnosis, crop plant fertilization, microbiology, and remote-sensing. As a gues<sup>t</sup> editor, I would like to express my gratitude to the authors and co-authors of the selected papers for their efforts in transfering the achievements and knowledge in their work on producing food to those who need support in the conditions arising from the present global challenges.

> **Witold Grzebisz** *Editor*
