In a global perspective, the agricultural sector is right now facing its biggest challenge ever. The world population is rapidly increasing, and food production has to grow at the same, or higher, speed to be able to feed everyone. At the same time, the effect on environmental and natural resources must be limited. Over-fertilization must be stopped to secure aquatic environments and to reduce greenhouse gas emissions, caused by production and use of inorganic fertilizers. For production of P fertilizer, furthermore a non-renewable natural resource is used, which is expected to be exhausted within 50-100 years if the present pattern of consumption is continued. Optimizing fertilizer addition in plant production is therefore necessary to obtain a higher production along with a reduced environmental impact. To succeed with this, it is, however, necessary to enable plant producers to diagnose the nutritional status of crops during the growing season, and at a stage sufficiently early not to threaten harvest yields. The purpose of this project has therefore been to develop new methods for early diagnosis of nutrient deficiencies in plants.

In Paper I, a review, the most frequently used techniques for soil and plant analysis are
described and the usability of each technique is discussed. Focus is put particularly on the newest methods for plant analysis based on fast spectroscopy, such as visual and near-infrared (Vis-NIR) reflectance and chlorophyll a fluorescence. These methods enable easy, fast and cheap determination of the nutritional status of plants concerning one or more nutrients. Thereby the addition of fertilizer can be managed precisely during the growing season. Insufficient validation or erroneous use, however, often results in doubtful outcomes or, in practical application, a poor use of the added fertilizer. This is presented along with a discussion of the perspectives in the new approach to plant analysis, which is possible using fast spectroscopy.

Paper II demonstrates that Cu deficient plants can be separated from healthy plants by
measuring NIR reflectance directly on fresh barley leaves. The method is specific for Cu, and the condition can be diagnosed so early that it is reversible. Paper III describes a method to diagnose P deficiency in barley plants and quantify P concentration in deficient plants. It was found that the I-step in the OJIP transient, which is the outcome of measuring chlorophyll a fluorescence, gradually straightens and disappears as P deficiency is induced, and this is used in the method. A similar change was found in tomato plants, indicating that this could be a general effect on photosynthesis. There are further indications that also deficiencies of Mg, Cu, S and Fe may have so far unknown, specific effects on the OJIP transient. A patent application has been filed on the method, enclosed as Paper IV.

The obtained results can relatively simply be further developed into actual instruments, as both NIR and chlo ophyll a fluorescence are already widely used methods. Such instruments can help plant producers by optimizing nutrient addition of Cu and P, and there are clear indications that similar methods for further nutrients can be identified, to the benefit of agriculture as well as environment.