Method for the fertilization of soil for cultivated plants

A method for the fertilization of soil for cultivated plants, whereby nitrogen fertilizer is spread over the cultivated area in conjunction with the sowing of cultivated plants and later during the growing season more fertilizer is spread over the cultivated area. In this method, a basic amount of fertilizer corresponding to a basic crop smaller than the maximum crop is spread over the cultivated area in conjunction with the sowing; a supplementary amount or fertilizer is spread on a limited area; the growth that has taken place in the cultivated area and in the area with supplementary fertilization during a certain time since the beginning of the growing season is measured; the measured growth that has taken place in the cultivated area is compared with the measured growth of the plants that has taken place in the area with supplementary fertilization in the same growing conditions, and, if the growth in the area with supplementary fertilization exceeds the growth in the cultivated area, supplementary fertilization is carried out in the cultivated area, corresponding to the growth of the plants in the area with supplementary fertilization as compared with the growth of the plants in the cultivated area and to the amount of fertilizer used in the cultivated area.

FIELD OF THE INVENTION
 The present invention relates to a method for the fertilization of soil for
 cultivated plants, whereby nitrogen fertilizer is spread over the
 cultivated area in conjunction with the sowing of cultivated plants and
 more fertilizer is spread over the cultivated area later during the
 growing season.
 In particular, the present invention relates to nitrogen fertilization
 carried out in conjunction with the cultivation of cereals, although the
 method can be applied in conjunction with the fertilization of soil for
 other plants as well by making corresponding changes in the amounts of
 fertilizer, In this context, `cereals` refers to all known cereals, such
 as wheat, barley, oats, rye, rape, turnip rape, maize, rice, etc. `Other
 plants` refers to other useful plants cultivated on fields and
 corresponding cultivation areas. In the present application, 1 kg of
 nitrogen fertilizer specifically means an amount of fertilizer that
 contains 1 kg of nitrogen.
 BACKGROUND OF THE INVENTION
 In field husbandry, in principle the soil should be fertilized with
 nitrogen used in amounts corresponding to the quantity of nitrogen removed
 from the soil via harvesting. Fertilization recommendations are based on
 long-term average crop yields obtained from extensive test material. The
 recommendations ignore the fact that there are large variations between
 growing seasons in respect of the formation of crop yields. Water supply
 is often a minimum factor restricting growth, and when water is in short
 supply, the crops per hectare fall below the long-term averages.
 Furthermore, because Finland is situated at the northern limits of the
 cultivable area, from time to time there are fail-years, e.g. due to cold
 weather conditions, in which the crops remain considerably be-low
 long-term averages. In other countries as well, the crops per hectare vary
 correspondingly, due to variations in the growing conditions, in the first
 place weather conditions.
 According to the fertilization recommendation for Finland, the average
 amount of nitrogen fertilizer to be spread on the cultivated area in
 mineral soil is 90-110 kg/ha. If the amount of fertilizer used is 110
 kg/ha, the crop yield should be over 5000 kg/ha for the amount of nitrogen
 removed from the soil with the crop to correspond to the amount of
 nitrogen spread over the cultivated area in conjunction with sowing. Very
 often, however, e.g. when growth is limited by insufficient water supply,
 the crops per hectare fall as low as below 3000 kg/ha. In this case, a
 large overdose of nitrogen remains in the soil, and this nitrogen is
 liable to be washed away, denitrified, or it may combine with the soil in
 a form unusable for plants. The average crops in Finland in recent years
 have been slightly over 3000 kg/ha. Therefore, in the long term, the
 fields have been over-fertilized. In other countries, too, there are large
 variations in crops, depending on the weather and other conditions
 prevailing in each country and their changes. However, the problem
 resulting from over-fertilization is encountered in other countries as
 well, especially when there are unexpected changes in weather conditions
 and in the case of drought.
 The fertilizer left unused because of over-fertilization, i.e. the
 production investment corresponding to the excess amount of fertilizer,
 has not yielded any returns In cultivation. In addition, the excess
 nitrogen is mainly washed away into water systems, resulting in a
 significant increase in the nitrogen load on water systems and therefore
 pollution. Moreover, in this case the fodder and food industries cannot
 get raw material of a quality consistent with the aim.
 SUMMARY OF THE INVENTION
 The object of the present invention is to eliminate the drawbacks described
 above.
 Thus, the object of the invention is to develop methods for fertilizing the
 soil for cultivated plants in such a way that the grower will get a better
 return on the production investment made in the form of fertilization and
 that the amount of fertilizer washed away into water systems and polluting
 them will be substantially reduced.
 A specific object of the invention is to develop fertilizing methods so
 that the fertilization carried out in conjunction with the sowing should
 better correspond to realistic crop prospects in the light of the average
 crops per hectare obtained in recent years. A further object of the
 invention is to develop methods for fertilizing the soil for cultivated
 plants in such a way that the amount of fertilizer spread on the
 cultivated area should more effectually correlate with possible larger
 crops as well.
 As for the features characteristic of the invention, reference is made to
 the claims.
 The invention is based on extensive investigations, during which it was
 unexpectedly established that the growth and/or nitrogen nutrient
 situation of cultivated plants, i.e. the need for nitrogen fertilization
 and the utilization of fertilizer by the plants can be measured during the
 growing season and, based on the measurement results, supplementary
 fertilization can be carried out as needed. In particular, the method is
 based on measuring the growth and/or nitrogen nutrient situation, e.g. the
 chlorophyll concentration, of cultivated plants during a certain period of
 time from the beginning of the growing season when an amount of fertilizer
 corresponding to a basic crop smaller than the local maximum crop is used
 and, similarly, on measuring the growth of cultivated plants in the same
 growing conditions in an area with supplementary fertilization, e.g. an
 over-fertilized area (e.g. a limited part of the cultivated area), where
 an overdose of fertilizer has been added so that the plants in this
 limited fertilizer window area can take as much nitrogen as they are able
 to take and utilize in the prevailing conditions; the amount of nitrogen
 fertilizer added in the fertilizer window may be e.g. 30-50% above the
 amount used in the rest of the cultivated area. A particularly
 advantageous approach is to determine the chlorophyll concentration in the
 plant leaves in the fertilizer window and outside it; it has been
 established that the chlorophyll concentration correlates quite well with
 the amount of nitrogen contained in the plant leaves, and so the
 chlorophyll concentration in the fertilizer window and outside it gives a
 relatively accurate indication of the amount of nitrogen fertilizer used
 by the plants and therefore of the amount of nitrogen needed in the
 production area. From the measurement of the growth of the plants in the
 cultivated area as compared with the growth in the area with supplementary
 fertilization, it is thus possible to establish whether the plants in the
 cultivated area are suffering from under-fertilization, and if so then
 this can be corrected via general supplementary fertilization of the
 cultivated area if the growth in the extra-fertilized area significantly
 exceeds the growth in the cultivated area.
 The amount of growth in a given area can be measured by any method known in
 itself, e.g. by weighing the growth per unit area that has taker. place in
 the area, e.g. the amount of aerial growth, i.e. phytomass, or if desired,
 the entire growth, i.e. biomass (comprising aerial parts and roots).
 The growth of cultivated plants can thus be monitored by measuring the
 nitrogen nutrient situation of the plants, e.g. by determining the
 chlorophyll concentration in the plants in a cultivated area with basic
 fertilization and in an area with supplementary fertilization.
 Supplementary fertilization is carried out if the growth and/or the amount
 of nitrogen, e.g. the chlorophyll concentration in the plants in the area
 with supplementary fertilization is substantially, e.g. over 10%,
 preferably over 20%, greater than in the cultivated area without
 supplementary fertilization.
 In conjunction with the investigations, methods for predicting the crop
 yield at a given time in the growing season so that it is possible already
 during the growing season to relatively accurately determine the
 prospective crop yield and the supplementary fertilization that may be
 required on the basis of the forecast and/or the growth that has already
 taken place during the growing season.
 A new feature in the method is especially the principle of measuring the
 growth in an area with basic fertilization during the growing season and
 comparing it with measured growth that has taken place in an
 over-fertilized area and determining the need for supplementary
 fertilization on the basis of these measurements. Another new feature in
 the method is that the nitrogen nutrient situation and/or chlorophyll
 situation of cultivated plants is determined during the growing season in
 an area with basic fertilization and that the need for supplementary
 fertilization is determined on this basis. A further new feature in the
 method is that, to determine the amount of supplementary fertilization
 required, the prospective crop, i.e. the crop forecast and the amount of
 nitrogen contained in the plants as measured during the growing season are
 combined with the amount of fertilizer used.
 According to the invention, a basic amount of fertilizer corresponding to a
 basic crop smaller than the maximum crop is spread over the cultivated
 area in conjunction with the sowing. In a limited portion of the
 cultivated area, e.g. in a so-called fertilizer window, an amount of
 supplementary fertilizer is spread. Later during the growing season, the
 amounts of growth that have taken place in the area with basic
 fertilization and in the area with supplementary fertilization are
 determined and these values are compared with each other and the need for
 supplementary fertilization is determined on the basis of this comparison
 and the basic fertilization in the cultivated area. Instead of determining
 the growth of the cultivated plants, it is possible to determine the
 amounts of nitrogen and/or chlorophyll measured in the cultivated plants
 in the basic fertilization area and in the extra fertilization area; the
 need for supplementary fertilization can be determined on the basis of
 these measurements as above.
 A crop forecast can be estimated after the sowing on the basis of the
 phytomass and heat summation accumulated during the growing season between
 the time of sowing and the time of measurement, based e.g. on the known
 fact that the heat summation up to the ripening of the crop is about
 1000.degree. in Finland and e.g. about 1300.degree. in Central Europe; the
 heat summation is calculated by summing the mean values of the
 temperatures, taken at 0800 hrs, 1400 hrs and 2000 hrs, measured in
 degrees Celsius and reduced by 5.degree. C., for each day within the
 calculating period. Thus, a crop forecast can be estimated on the basis of
 the phytomass, the heat summation and an estimated or statistically
 calculated heat summation for the remaining growing period. It is to be
 noted that the numeric value of the heat summation for an area where the
 method is applied has no importance in itself, in other words, the heat
 summation for an area may be e.g. 1000.degree., as in Finland, or
 1300.degree., as in Central Europe, or some other numeric value. The heat
 summation can be used to produce a crop forecast during the growing
 season, and the crop forecast can be used to estimate the need for
 supplementary fertilization in order to achieve a crop consistent with the
 crop forecast.
 The supplementary fertilization can be carried out by any method known in
 itself, e.g by applying the fertilizer in the form of conventional
 granular nitrogen fertilizer, as a water solution dosed onto the plant
 leaves, in conjunction with weed killing or other spraying treatment of
 growth, or generally by any method, as is known in the art. The
 supplementary fertilization may be carried out in one phase or several
 phases.
 The amount of nitrogen fertilizer spread in conjunction with the sowing is
 preferably about 70.+-.10% of the amount of fertilizer corresponding to
 the maximum crop. The amount of nitrogen fertilizer spread in conjunction
 with basic fertilization may also be larger or smaller than this. The
 maximum crop can be defined e.g. as a general average maximum crop for the
 cultivated area in question or as some other generally known maximum crop
 value.
 Supplementary fertilization is preferably carried out if the difference
 between the crop forecast and the basic crop is over 10%, preferably over
 20% of the crop forecast.
 It is to be noted that the above amounts of fertilizer per unit area and
 the amounts of crop per unit area apply in the first place to Nordic, i.e.
 Finnish conditions. In other countries, the amounts of fertilizer and crop
 may vary greatly depending on conditions like moisture, temperature,
 weather in general, soil quality, plants cultivated, expected harvest etc.
 according to circumstances in general, The essential point in the
 invention is expressly that it provides a general method in principle for
 determining the need for supplementary fertilization and for carrying out
 supplementary fertilization.
 The invention makes it possible to adjust the amount of fertilizer to be
 spread on the cultivated area so that it closely corresponds to the actual
 growing conditions so as to avoid over-fertilization in bad growing
 conditions and, on the other hand, to give the plants the required larger
 amount of fertilizer corresponding to a larger crop in good growing
 conditions, thus ensuring a maximal crop. Furthermore, the invention makes
 it possible for a grower who uses the fertilization method of the
 invention to get full and maximal returns on the production investment
 corresponding to the amount of fertilizer used in a given growing area,
 mainly regardless of the growing conditions during the growing season.
 Further, the invention allows a nearly zero nitrogen balance to be
 maintained in the cultivated area, so that the amount of nitrogen spread
 over the cultivated area via fertilization corresponds to the amount of
 nitrogen mainly removed from the cultivated area along with grains and
 straw via harvesting. Thus, no fertilizer is washed away into water
 systems and in this respect pollution of water systems remains under
 control.
 In addition, the invention provides the advantage that, in each growing
 season, food and fodder industries receive the required amount of raw
 material having the quality aimed at. Moreover, the crop yield can be
 accurately predicted during the growing season and is therefore known to
 the industry before harvesting. Consequently, resources corresponding as
 closely as possible to the actual crop can be reserved in advance for the
 handling and storage of the crop.
 In addition to the obvious advantages mentioned above, the invention
 substantially improves the efficiency of cultivation of cultivated plants,
 which in turn generally improves the profitability and economy of the food
 and fodder industry and food supply in general, This has a very great
 general importance after the recent major political changes and
 integration development.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 EXAMPLE 1
 Fertilization in a Dry Growing Season
 In this example, the amount of nitrogen fertilizer was 120 kg,
 corresponding to a fair grain crop of over 5000 kg/ha, FIG. 1. However,
 the growing season is dry, which means that growth is restricted by a
 shortage of water, and the crop yield remains as low as under 3000 kg of
 grain per hectare, The amount of nitrogen removed with the grains from the
 cultivated area via harvesting is 80 kg/ha, and the amount of nitrogen
 remaining in the soil is 40 kg/ha. With the autumn rains, the excess
 nitrogen begins to be washed away into the water system, and part of it is
 denitrified into the air.
 In a growing year like this, the grower gets no return on the amount of
 nitrogen left in the soil, and in addition, due to the excess of nitrogen,
 the protein content of the corn is too high and its energy content is low,
 so fodder industry cannot get the kind of corn aimed at.
 This example describes fertilization in a dry growing season in Finland and
 it shows the amounts of fertilizer typically used in Finland as well as
 the corresponding grain crops. The above numeric values for the amounts of
 fertilizer and crop could be replaced with amounts of fertilizer and crop
 obtained via local measurement,
 EXAMPLE 2
 Fertilization According to Growing Season
 The amount of fertilizer used is 90 kg/ha, corresponding to a grain crop of
 about 3500 kg/ha. In the course of the growing season, e.g. at the 4-leaf
 stage (t.sub.1), a crop forecast is calculated using the phytomass and
 heat summation accumulated between the time of sowing (t.sub.0) and the
 time of measurement (t.sub.1). At the same time, the chlorophyll
 concentration in the plant leaves is determined in an over-fertilized
 fertilizer window and in the cultivated area. The crop forecast and the
 chlorophyll concentration (proportional to nitrogen concentration) in the
 fertilizer window are over 40% higher as compared with the basic crop of
 3000 kg/ha and the corresponding chlorophyll concentration in the
 cultivated area. Based on this determination, the crop forecast is
 corrected upwards (about 40%) to the value of 5000 kg/ha, and
 supplementary nitrogen fertilization at 30 kg/ha (nearly 40%) is carried
 out. In this example, the supplementary fertilization is carried out in
 one stage, but if desirable, it can also be performed in several stages.
 In conjunction with the harvesting it is found that the crop is 5000 kg/ha,
 the amount of nitrogen removed during harvesting from the cultivated area
 with the grains is 100 kg/ha and, correspondingly, the amount of nitrogen
 removed with the straw is 20 kg/ha, so the nitrogen balance remains
 constant.
 If the crop forecast and/or the measurement of chlorophyll, concentration
 in the plant leaves at time t.sub.1 should give a crop prospect of only
 3000 kg/ha, supplementary fertilization would be omitted, in which case
 the original basic fertilization with 90 kg/ha would yield a maximal crop
 in the particular growing conditions. Thus, the extra cost of
 supplementary fertilization is avoided and the grower can get a full
 return on the production investment made in the form of fertilization.
 The example represents fertilization in a dry growing season in Finland and
 it shows the amounts of fertilizer typically used in Finland as well as
 the corresponding amounts of grain crop.
 EXAMPLE 3
 In this example, fertilization was carried out on 4 test areas and the
 grain crop produced/amount of fertilizer used was calculated in
 conjunction with harvesting. The results are presented in Table 1.
 TABLE 1
 Grain produced/nitrogen fertilizer used
 Method of fertilization kg/kg
 1 50
 2 54
 3 52
 1 - basic fertilization 130 kg of nitrogen/ha, no supplementary
 fertilization
 2 - basic fertilization 80 kg of nitrogen/ha, supplementary fertilization 3
 .times. 15 kg/ha
 3 - basic fertilization 100 kg of nitrogen/ha, supplementary fertilization
 2 .times. 15 kg/ha
 The supplementary fertilization was mainly provided through the foliage by
 spraying.
 This embodiment example shows that nitrogen supplied via the foliage yields
 a larger crop than nitrogen supplied in the conventional manner via the
 soil, especially when supplementary fertilization is carried out by the
 method of the invention by determining a crop forecast on the basis of the
 heat summation and the phytomass accumulated between the time of sowing
 and the time of measurement.
 EXAMPLE 4
 In this example, the basic amount of fertilizer on a feed grain field was
 80 kg of N/ha, corresponding to a crop of 3000 kg/ha. Supplementary
 fertilization at 30 kg/ha was carried out in a fertilizer window, When the
 feed grain (barley) was at the straw growing stage, the phytomass was
 weighed in the cultivated area and in the fertilizer window, the results
 were 0.800 kg/m.sup.2 and 0.920 kg/m.sup.2 respectively. From this growth
 determination, it can be concluded that growth of the cultivated plants in
 the fertilizer window, where there was a sufficient supply of fertilizer,
 was about 15% higher than in the cultivated area. Based on this
 calculation, 15% supplementary fertilization is carried out, i.e. an
 additional 12 kg of nitrogen/ha is spread on the field.
 EXAMPLE 5
 In this example, the basic fertilization for a corn (oats) field is 90 kg
 of N/ha, corresponding to a corn crop of 3500 kg/ha. The amount of
 fertilizer used in a fertilizer window is 120 kg/ha. At the straw growing
 stage of the corn, the chlorophyll concentration in the plant leaves was
 determined using a so-called Spad meter. The result of the spad
 measurement on the cultivated area is 40 Spad units, while that of the
 Spad measurement on the fertilizer window is 53 Spad units. Based on the
 measurement, a decision is made to carry out supplementary fertilization
 as follows:
 ##EQU1##
 If it is desired to raise the chlorophyll concentration (i.e. nitrogen
 contents) 1 Spad unit, supplementary fertilization may be carried out
 ##EQU2##
 The embodiment examples are intended to illustrate the invention without
 limiting it in any way.