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Low pH and potassium deficiency are main types of nutritional stress under conditions of the Eastern Croatia. As corn is most spread arable crop (1) in Croatia (harvested area about half million hectares or third part of arable land capacity), nutritional stress is analyzed with aspect of corn breeding possibilities for alleviation of this problem. Also, growing of more tolerant genotypes under less favorable environment is possible direction of sustainable agriculture strategy. Material and methods Ten different corn (Zea mays L.) hybrids of different origin were grown during the growing season of 1993 under field conditions. Three experimental fields are situated in the Eastern Croatia and they are distanced (by air-line) from Osijek (capital of province) approximately 30 km in S direction (the experiment 1), 25 km in S direction (the experiment 2) and 75 km in SW direction (the experiment 3). The experimental fields 1 and 2 are situated in the lowland area of altitude above sea-level between 90 and 100m, while the experimental field 3 is situated in hill area (altitude 170m) of the province. The soils are classified as drained gleysol (the experiment 1: soil stress due to K deficiency) and planosol (the exp. 2 and the exp. 3: soil stress due to low pH in both soils and due to high level of soluble Al in the soil of the 3) - Table I. The field experiments were sown in the third decade of April and they were harvested in the third decade of September (the experiment 1) and in the second decade of October (the remain two experiments). Three experiments were conducted in four replications. The experimental plot measured 18.2m2, 8.05m2 and 7.18m2 for the experiment 1, 2 and 3, respectively. Planned plant densities were 57140 plant/ha (the experiment s 2 and 3), while in the experiment 2 they were different as follows: 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids of the experiment 1 - Table II). Grain yields were calculated on 14% moisture basis and realized plant density with corrections for female-sterile plants contribution. Plant available phosphorus, potassium and aluminum were determined by AL-method (2). Results and discussion Grain yields of maize are under influences of environmental and inheritance factors. Low degree of soil fertility induced by poor chemical properties (for example, very acid or alkaline soils, nutrient deficiencies or excess of some elements) is possible to improve by adequate soil management practice. However, today is actual strategy of adaptation of plants to less favorable soil properties by adequate program of plant breeding. For this reason, we tested response of maize hybrids under different soil conditions. Potassium disorders in maize are widespread on the gleysols of east Croatia. Such soils contain low levels of exchangeable K, high levels of exchangeable Ca and Mg, and are strongly K-fixing. By application of enormous rates of K fertilizer (KCl form) until 2220 kg K/ha, grain yields of maize were normalized and increased a few times in comparison to control (3). However, grain yields of maize under these soil stress conditions are considerable different depending on hybrid. For example, by our earlier investigations (4), seven maize hybrids including Os1-48 inbred line as parent have been more tolerant (average grain yield 5.64 t/ha) in comparison with seven hybrids including Os87-24 inbred line as parent (average grain yield 4.16 t/ha). Ten maize hybrids under identical soil conditions characterizing K deficiency (the experiment 1) showed differences of grain yields from 1.04 t/ha to 2.63 t/ha and OsSK553 and OsSK377 maize hybrids were more tolerant to K deficiency than remaining eight tested hybrids (Table II). Low soil pH in combination with high levels of soluble aluminum (the experiment 3) is also serious problem. Under these soil stress conditions, grain yields of ten maize hybrids were in range from 3.72 to 5.75 t/ha (Table II). OsSK513 hybrid was most tolerant to this type of soil stress. Soil conditions of the experiment 3 was more favorable for maize growth in comparison with conditions of remaining two experiments because only low pH was stress factor. Under these conditions, grain yields of maize (from 5.36 to 8.02 t/ha) were nearly to normal yields. High-yielding OsSK552 and OsSK644 hybrids showed high yield under acid soil conditions (Table II). Beside soil improvement by adequate soil management practice, growing of stress tolerant maize hybrids is direction for increase of maize yield under less favorable environmental conditions. Conclusions Corn hybrids are different degree of soil stress tolerance. For example, grain yield of the most susceptible hybrid was 60% lower, 33% lower and 35% lower in comparison with grain yield of the most tolerant hybrid for the exp. 1, 2 and 3, respectively (Table II). Especially low grain yield and low plant density realization were found under soil stress induced by K deficiency. Also, low pH value in combination with high soluble-aluminum content resulted by lower corn yields in comparison with those under low pH stress only. We presume that by adequate corn breeding strategy (development of more tolerant corn hybrids to different types of soil stress) is possible to increase grain yields under less favorable soil conditions. References 1Kovacevic V., Josipovic M. and Grgic D.: Pregled rezultata proizvodnje kukuruza u Slavoniji i Baranji (1960-1989.g). Poljopr. aktualnosti 30 (1994), 141-151. 2Egner H., Riehm H., Domingo W. R.: Untersuchungen uber die chemische Bodenanalyse als Grundlage fur die Beurteilung des Nahrstoffzustandes der Boden: I. Chemische Extractionmethoden zur Phosphor- und Kaliumbestimmung. Kungliga Lantbrukshogskolans Annaler, Uppsala 26, (1960), 199-215. 3 Kovacevic V., and Vukadinovic V. : The potassium requirements of maize and soyabean on a high K-fixing soil. S. Afr. J. Plant Soil 9, (1992), 10-13. 4 Kovacevic V. and Vujevic S. (1993): Magnesium uptake and lodging tolerance in maize (Zea mays L.) hybrids. In Magnesium 1993, ed. S. Golf, D. Dralle and L. Vecchiet (London: John Libbey Company Ltd. 1993), 99-104. Table I. Soil properties (0-30cm of depth: stress factor underlined) pHHumusmg/100 g of soil ExperimentH2OKCl (%)P2O5K2OAl 18.17.22.417.58.9- 25.14.21.812.322.5- 35.04.01.812.923.29.3 Table II. Corn grain yield (t/ha) and plant density realization (% of total) The experiment 1The experiment 2The experiment 3 Hybridt/ha%*Hybridt/ha%*Hybridt/ha%* OsSK332 OsSK377 OsSK 382 OsSK391 OsSK403 OsSK552 OsSK553 OsSK554 OsSK644 Bc66-611.92 2.47 2.14 1.50 1.04 1.46 2.63 2.08 1.60 1.5465.8 68.4 67.2 66.6 66.8 66.2 83.6 71.1 59.1 71.1OsSK262 OsSK218 OsSK 377 OsSK382 OsSK456OsSK502OsSK552 OsSK553 Bc66-61 OsSK6445.36 5.57 5.87 7.52 5.92 6.52 8.00 5.77 6.76 8.0284.5 91.3 89.1 95.7 84.3 91.9 92.4 94.6 89.7 87.0OsSK332 OsSK412 OsSK513 148-8886 8424-8639 OsSK382 8424-8886 8639-8724 8639-8886 8724-88865.11 4.62 5.75 5.32 4.30 4.53 4.40 5.09 3.72 4.8895.0 93.1 90.6 86.2 93.1 92.5 93.1 90.6 96.9 90.0 Mean1.8468.6Mean6.5390.1Mean 4.7792.1 LSD 0.05 LSD 0.010.27 0.36LSD 0.05 LSD 0.010.78 1.06LSD 5% LSD 1%0.43 0.58 * 100% plants/ha (the exp. 1) = 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids) ; 100% plants/ha (the exp. 2 and 3) = 57140 ; Introduction Low pH and potassium deficiency are main types of nutritional stress under conditions of the Eastern Croatia. As corn is most spread arable crop (1) in Croatia (harvested area about half million hectares or third part of arable land capacity), nutritional stress is analyzed with aspect of corn breeding possibilities for alleviation of this problem. Also, growing of more tolerant genotypes under less favorable environment is possible direction of sustainable agriculture strategy. Material and methods Ten different corn (Zea mays L.) hybrids of different origin were grown during the growing season of 1993 under field conditions. Three experimental fields are situated in the Eastern Croatia and they are distanced (by air-line) from Osijek (capital of province) approximately 30 km in S direction (the experiment 1), 25 km in S direction (the experiment 2) and 75 km in SW direction (the experiment 3). The experimental fields 1 and 2 are situated in the lowland area of altitude above sea-level between 90 and 100m, while the experimental field 3 is situated in hill area (altitude 170m) of the province. The soils are classified as drained gleysol (the experiment 1: soil stress due to K deficiency) and planosol (the exp. 2 and the exp. 3: soil stress due to low pH in both soils and due to high level of soluble Al in the soil of the 3) - Table I. The field experiments were sown in the third decade of April and they were harvested in the third decade of September (the experiment 1) and in the second decade of October (the remain two experiments). Three experiments were conducted in four replications. The experimental plot measured 18.2m2, 8.05m2 and 7.18m2 for the experiment 1, 2 and 3, respectively. Planned plant densities were 57140 plant/ha (the experiment s 2 and 3), while in the experiment 2 they were different as follows: 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids of the experiment 1 - Table II). Grain yields were calculated on 14% moisture basis and realized plant density with corrections for female-sterile plants contribution. Plant available phosphorus, potassium and aluminum were determined by AL-method (2). Results and discussion Grain yields of maize are under influences of environmental and inheritance factors. Low degree of soil fertility induced by poor chemical properties (for example, very acid or alkaline soils, nutrient deficiencies or excess of some elements) is possible to improve by adequate soil management practice. However, today is actual strategy of adaptation of plants to less favorable soil properties by adequate program of plant breeding. For this reason, we tested response of maize hybrids under different soil conditions. Potassium disorders in maize are widespread on the gleysols of east Croatia. Such soils contain low levels of exchangeable K, high levels of exchangeable Ca and Mg, and are strongly K-fixing. By application of enormous rates of K fertilizer (KCl form) until 2220 kg K/ha, grain yields of maize were normalized and increased a few times in comparison to control (3). However, grain yields of maize under these soil stress conditions are considerable different depending on hybrid. For example, by our earlier investigations (4), seven maize hybrids including Os1-48 inbred line as parent have been more tolerant (average grain yield 5.64 t/ha) in comparison with seven hybrids including Os87-24 inbred line as parent (average grain yield 4.16 t/ha). Ten maize hybrids under identical soil conditions characterizing K deficiency (the experiment 1) showed differences of grain yields from 1.04 t/ha to 2.63 t/ha and OsSK553 and OsSK377 maize hybrids were more tolerant to K deficiency than remaining eight tested hybrids (Table II). Low soil pH in combination with high levels of soluble aluminum (the experiment 3) is also serious problem. Under these soil stress conditions, grain yields of ten maize hybrids were in range from 3.72 to 5.75 t/ha (Table II). OsSK513 hybrid was most tolerant to this type of soil stress. Soil conditions of the experiment 3 was more favorable for maize growth in comparison with conditions of remaining two experiments because only low pH was stress factor. Under these conditions, grain yields of maize (from 5.36 to 8.02 t/ha) were nearly to normal yields. High-yielding OsSK552 and OsSK644 hybrids showed high yield under acid soil conditions (Table II). Beside soil improvement by adequate soil management practice, growing of stress tolerant maize hybrids is direction for increase of maize yield under less favorable environmental conditions. Conclusions Corn hybrids are different degree of soil stress tolerance. For example, grain yield of the most susceptible hybrid was 60% lower, 33% lower and 35% lower in comparison with grain yield of the most tolerant hybrid for the exp. 1, 2 and 3, respectively (Table II). Especially low grain yield and low plant density realization were found under soil stress induced by K deficiency. Also, low pH value in combination with high soluble-aluminum content resulted by lower corn yields in comparison with those under low pH stress only. We presume that by adequate corn breeding strategy (development of more tolerant corn hybrids to different types of soil stress) is possible to increase grain yields under less favorable soil conditions. References 1Kovacevic V., Josipovic M. and Grgic D.: Pregled rezultata proizvodnje kukuruza u Slavoniji i Baranji (1960-1989.g). Poljopr. aktualnosti 30 (1994), 141-151. 2Egner H., Riehm H., Domingo W. R.: Untersuchungen uber die chemische Bodenanalyse als Grundlage fur die Beurteilung des Nahrstoffzustandes der Boden: I. Chemische Extractionmethoden zur Phosphor- und Kaliumbestimmung. Kungliga Lantbrukshogskolans Annaler, Uppsala 26, (1960), 199-215. 3 Kovacevic V., and Vukadinovic V. : The potassium requirements of maize and soyabean on a high K-fixing soil. S. Afr. J. Plant Soil 9, (1992), 10-13. 4 Kovacevic V. and Vujevic S. (1993): Magnesium uptake and lodging tolerance in maize (Zea mays L.) hybrids. In Magnesium 1993, ed. S. Golf, D. Dralle and L. Vecchiet (London: John Libbey Company Ltd. 1993), 99-104. Table I. Soil properties (0-30cm of depth: stress factor underlined) pHHumusmg/100 g of soil ExperimentH2OKCl (%)P2O5K2OAl 18.17.22.417.58.9- 25.14.21.812.322.5- 35.04.01.812.923.29.3 Table II. Corn grain yield (t/ha) and plant density realization (% of total) The experiment 1The experiment 2The experiment 3 Hybridt/ha%*Hybridt/ha%*Hybridt/ha%* OsSK332 OsSK377 OsSK 382 OsSK391 OsSK403 OsSK552 OsSK553 OsSK554 OsSK644 Bc66-611.92 2.47 2.14 1.50 1.04 1.46 2.63 2.08 1.60 1.5465.8 68.4 67.2 66.6 66.8 66.2 83.6 71.1 59.1 71.1OsSK262 OsSK218 OsSK 377 OsSK382 OsSK456OsSK502OsSK552 OsSK553 Bc66-61 OsSK6445.36 5.57 5.87 7.52 5.92 6.52 8.00 5.77 6.76 8.0284.5 91.3 89.1 95.7 84.3 91.9 92.4 94.6 89.7 87.0OsSK332 OsSK412 OsSK513 148-8886 8424-8639 OsSK382 8424-8886 8639-8724 8639-8886 8724-88865.11 4.62 5.75 5.32 4.30 4.53 4.40 5.09 3.72 4.8895.0 93.1 90.6 86.2 93.1 92.5 93.1 90.6 96.9 90.0 Mean1.8468.6Mean6.5390.1Mean 4.7792.1 LSD 0.05 LSD 0.010.27 0.36LSD 0.05 LSD 0.010.78 1.06LSD 5% LSD 1%0.43 0.58 * 100% plants/ha (the exp. 1) = 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids) ; 100% plants/ha (the exp. 2 and 3) = 57140 ; Introduction Low pH and potassium deficiency are main types of nutritional stress under conditions of the Eastern Croatia. As corn is most spread arable crop (1) in Croatia (harvested area about half million hectares or third part of arable land capacity), nutritional stress is analyzed with aspect of corn breeding possibilities for alleviation of this problem. Also, growing of more tolerant genotypes under less favorable environment is possible direction of sustainable agriculture strategy. Material and methods Ten different corn (Zea mays L.) hybrids of different origin were grown during the growing season of 1993 under field conditions. Three experimental fields are situated in the Eastern Croatia and they are distanced (by air-line) from Osijek (capital of province) approximately 30 km in S direction (the experiment 1), 25 km in S direction (the experiment 2) and 75 km in SW direction (the experiment 3). The experimental fields 1 and 2 are situated in the lowland area of altitude above sea-level between 90 and 100m, while the experimental field 3 is situated in hill area (altitude 170m) of the province. The soils are classified as drained gleysol (the experiment 1: soil stress due to K deficiency) and planosol (the exp. 2 and the exp. 3: soil stress due to low pH in both soils and due to high level of soluble Al in the soil of the 3) - Table I. The field experiments were sown in the third decade of April and they were harvested in the third decade of September (the experiment 1) and in the second decade of October (the remain two experiments). Three experiments were conducted in four replications. The experimental plot measured 18.2m2, 8.05m2 and 7.18m2 for the experiment 1, 2 and 3, respectively. Planned plant densities were 57140 plant/ha (the experiment s 2 and 3), while in the experiment 2 they were different as follows: 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids of the experiment 1 - Table II). Grain yields were calculated on 14% moisture basis and realized plant density with corrections for female-sterile plants contribution. Plant available phosphorus, potassium and aluminum were determined by AL-method (2). Results and discussion Grain yields of maize are under influences of environmental and inheritance factors. Low degree of soil fertility induced by poor chemical properties (for example, very acid or alkaline soils, nutrient deficiencies or excess of some elements) is possible to improve by adequate soil management practice. However, today is actual strategy of adaptation of plants to less favorable soil properties by adequate program of plant breeding. For this reason, we tested response of maize hybrids under different soil conditions. Potassium disorders in maize are widespread on the gleysols of east Croatia. Such soils contain low levels of exchangeable K, high levels of exchangeable Ca and Mg, and are strongly K-fixing. By application of enormous rates of K fertilizer (KCl form) until 2220 kg K/ha, grain yields of maize were normalized and increased a few times in comparison to control (3). However, grain yields of maize under these soil stress conditions are considerable different depending on hybrid. For example, by our earlier investigations (4), seven maize hybrids including Os1-48 inbred line as parent have been more tolerant (average grain yield 5.64 t/ha) in comparison with seven hybrids including Os87-24 inbred line as parent (average grain yield 4.16 t/ha). Ten maize hybrids under identical soil conditions characterizing K deficiency (the experiment 1) showed differences of grain yields from 1.04 t/ha to 2.63 t/ha and OsSK553 and OsSK377 maize hybrids were more tolerant to K deficiency than remaining eight tested hybrids (Table II). Low soil pH in combination with high levels of soluble aluminum (the experiment 3) is also serious problem. Under these soil stress conditions, grain yields of ten maize hybrids were in range from 3.72 to 5.75 t/ha (Table II). OsSK513 hybrid was most tolerant to this type of soil stress. Soil conditions of the experiment 3 was more favorable for maize growth in comparison with conditions of remaining two experiments because only low pH was stress factor. Under these conditions, grain yields of maize (from 5.36 to 8.02 t/ha) were nearly to normal yields. High-yielding OsSK552 and OsSK644 hybrids showed high yield under acid soil conditions (Table II). Beside soil improvement by adequate soil management practice, growing of stress tolerant maize hybrids is direction for increase of maize yield under less favorable environmental conditions. Conclusions Corn hybrids are different degree of soil stress tolerance. For example, grain yield of the most susceptible hybrid was 60% lower, 33% lower and 35% lower in comparison with grain yield of the most tolerant hybrid for the exp. 1, 2 and 3, respectively (Table II). Especially low grain yield and low plant density realization were found under soil stress induced by K deficiency. Also, low pH value in combination with high soluble-aluminum content resulted by lower corn yields in comparison with those under low pH stress only. We presume that by adequate corn breeding strategy (development of more tolerant corn hybrids to different types of soil stress) is possible to increase grain yields under less favorable soil conditions. References 1Kovacevic V., Josipovic M. and Grgic D.: Pregled rezultata proizvodnje kukuruza u Slavoniji i Baranji (1960-1989.g). Poljopr. aktualnosti 30 (1994), 141-151. 2Egner H., Riehm H., Domingo W. R.: Untersuchungen uber die chemische Bodenanalyse als Grundlage fur die Beurteilung des Nahrstoffzustandes der Boden: I. Chemische Extractionmethoden zur Phosphor- und Kaliumbestimmung. Kungliga Lantbrukshogskolans Annaler, Uppsala 26, (1960), 199-215. 3 Kovacevic V., and Vukadinovic V. : The potassium requirements of maize and soyabean on a high K-fixing soil. S. Afr. J. Plant Soil 9, (1992), 10-13. 4 Kovacevic V. and Vujevic S. (1993): Magnesium uptake and lodging tolerance in maize (Zea mays L.) hybrids. In Magnesium 1993, ed. S. Golf, D. Dralle and L. Vecchiet (London: John Libbey Company Ltd. 1993), 99-104. Table I. Soil properties (0-30cm of depth: stress factor underlined) pHHumusmg/100 g of soil ExperimentH2OKCl (%)P2O5K2OAl 18.17.22.417.58.9- 25.14.21.812.322.5- 35.04.01.812.923.29.3 Table II. Corn grain yield (t/ha) and plant density realization (% of total) The experiment 1The experiment 2The experiment 3 Hybridt/ha%*Hybridt/ha%*Hybridt/ha%* OsSK332 OsSK377 OsSK 382 OsSK391 OsSK403 OsSK552 OsSK553 OsSK554 OsSK644 Bc66-611.92 2.47 2.14 1.50 1.04 1.46 2.63 2.08 1.60 1.5465.8 68.4 67.2 66.6 66.8 66.2 83.6 71.1 59.1 71.1OsSK262 OsSK218 OsSK 377 OsSK382 OsSK456OsSK502OsSK552 OsSK553 Bc66-61 OsSK6445.36 5.57 5.87 7.52 5.92 6.52 8.00 5.77 6.76 8.0284.5 91.3 89.1 95.7 84.3 91.9 92.4 94.6 89.7 87.0OsSK332 OsSK412 OsSK513 148-8886 8424-8639 OsSK382 8424-8886 8639-8724 8639-8886 8724-88865.11 4.62 5.75 5.32 4.30 4.53 4.40 5.09 3.72 4.8895.0 93.1 90.6 86.2 93.1 92.5 93.1 90.6 96.9 90.0 Mean1.8468.6Mean6.5390.1Mean 4.7792.1 LSD 0.05 LSD 0.010.27 0.36LSD 0.05 LSD 0.010.78 1.06LSD 5% LSD 1%0.43 0.58 * 100% plants/ha (the exp. 1) = 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids) ; 100% plants/ha (the exp. 2 and 3) = 57140 ; Introduction Low pH and potassium deficiency are main types of nutritional stress under conditions of the Eastern Croatia. As corn is most spread arable crop (1) in Croatia (harvested area about half million hectares or third part of arable land capacity), nutritional stress is analyzed with aspect of corn breeding possibilities for alleviation of this problem. Also, growing of more tolerant genotypes under less favorable environment is possible direction of sustainable agriculture strategy. Material and methods Ten different corn (Zea mays L.) hybrids of different origin were grown during the growing season of 1993 under field conditions. Three experimental fields are situated in the Eastern Croatia and they are distanced (by air-line) from Osijek (capital of province) approximately 30 km in S direction (the experiment 1), 25 km in S direction (the experiment 2) and 75 km in SW direction (the experiment 3). The experimental fields 1 and 2 are situated in the lowland area of altitude above sea-level between 90 and 100m, while the experimental field 3 is situated in hill area (altitude 170m) of the province. The soils are classified as drained gleysol (the experiment 1: soil stress due to K deficiency) and planosol (the exp. 2 and the exp. 3: soil stress due to low pH in both soils and due to high level of soluble Al in the soil of the 3) - Table I. The field experiments were sown in the third decade of April and they were harvested in the third decade of September (the experiment 1) and in the second decade of October (the remain two experiments). Three experiments were conducted in four replications. The experimental plot measured 18.2m2, 8.05m2 and 7.18m2 for the experiment 1, 2 and 3, respectively. Planned plant densities were 57140 plant/ha (the experiment s 2 and 3), while in the experiment 2 they were different as follows: 54945 (OsSK644 and Bc66-61), 68027 (OsSK332 and OsSK377), 63492 (remaining six hybrids of the experiment 1 - Table II). Grain yields were calculated on 14% moisture basis and realized plant density with corrections for female-sterile plants contribution. Plant available phosphorus, potassium and aluminum were determined by AL-method (2). Results and discussion Grain yields of maize are under influences of environmental and inheritance factors. Low degree of soil fertility induced by poor chemical properties (for example, very acid or alkaline soils, nutrient deficiencies or excess of some elements) is possible to improve by adequate soil management practice. However, today is actual strategy of adaptation of plants to less favorable soil properties by adequate program of plant breeding. For this reason, we tested response of maize hybrids under different soil conditions. Potassium disorders in maize are widespread on the gleysols of east Croatia. Such soils contain low levels of exchangeable K, high levels of exchangeable Ca and Mg, and are strongly K-fixing. By application of enormous rates of K fertilizer (KCl form) until 2220 kg K/ha, grain yields of maize were normalized and increased a few times in comparison to control (3). However, grain yields of maize under these soil stress conditions are considerable different depending on hybrid. For example, by our earlier investigations (4), seven maize hybrids including Os1-48 inbred line as parent have been more tolerant (average grain yield 5.64 t/ha) in comparison with seven hybrids including Os87-24 inbred line as parent (average grain yield 4.16 t/ha). Ten maize hybrids under identical soil conditions characterizing K deficiency (the experiment 1) showed differences of grain yields from 1.04 t/ha to 2.63 t/ha and OsSK553 and OsSK377 maize hybrids were more tolerant to K deficiency than remaining eight tested hybrids (Table II). Low soil pH in combination with high levels of soluble aluminum (the experiment 3) is also serious problem. Under these soil stress conditions, grain yields of ten maize hybrids were in range from 3.72 to 5.75 t/ha (Table II). OsSK513 hybrid was most tolerant to this type of soil stress. Soil conditions of the experiment 3 was more favorable for maize growth in comparison with conditions of remaining two experiments because only low pH was stress factor. Under these conditions, grain yields of maize (from 5.36 to 8.02 t/ha) were nearly to normal yields. High-yielding OsSK552 and OsSK644 hybrids showed high yield under acid soil conditions (Table II). Beside soil improvement by adequate soil management practice, growing of stress tolerant maize hybrids is direction for increase of maize yield under less favorable environmental conditions. Conclusions Corn hybrids are different degree of soil stress tolerance. For example, grain yield of the most susceptible hybrid was 60% lower, 33% lower and 35% lower in comparison with grain yield of the most tolerant hybrid for the exp. 1, 2 and 3, respectively (Table II). Especially low grain yield and low plant density realization were found under soil stress induced by K deficiency. Also, low pH value in combination with high soluble-aluminum content resulted by lower corn yields in comparison with those under low pH stress only. We presume that by adequate corn breeding strategy (development of more tolerant corn hybrids to different types of soil stress) is possible to increase grain yields under less favorable soil conditions. References 1Kovacevic V., Josipovic M. and Grgic D.: Pregled rezultata proizvodnje kukuruza u Slavoniji i Baranji (1960-1989.g). Poljopr. aktualnosti 30 (1994), 141-151. 2Egner H., Riehm H., Domingo W. R.: Untersuchungen uber die chemische Bodenanalyse als Grundlage fur die Beurteilung des Nahrstoffzustandes der Boden: I. Chemische Extractionmethoden zur Phosphor- und Kaliumbestimmung. Kungliga Lantbrukshogskolans Annaler, Uppsala 26, (1960), 199-215. 3 Kovacevic V., and Vukadinovic V. : The potassium requirements of maize and soyabean on a high K-fixing soil. S. Afr. J. Plant Soil 9, (1992), 10-13. 4 Kovacevic V. and Vujevic S. (1993): Magnesium uptake and lodging tolerance in maize (Zea mays L.) hybrids. In Magnesium 1993, ed. S. Golf, D. Dralle and L. Vecchiet (London: John Libbey Company Ltd. 1993), 99-104. Table I. Soil properties (0-30cm of depth: stress factor underlined) pHHumusmg/100 g of soil ExperimentH2OKCl (%)P2O5K2OAl 18.17.22.417.58.9- 25.14.21.812.322.5- 35.04.01.812.923.29.3 Table II. Corn grain yield (t/ha) and plant density realization (% of total) The experiment 1The experiment 2The experiment 3 Hybridt/ha%*Hybridt/ha%*Hybridt/ha%* OsSK332 OsSK377 OsSK 382 OsSK391 OsSK403 OsSK552 OsSK553 OsSK554 OsSK644 Bc66-611.92 2.47 2.14 1.50 1.04 1.46 2.63 2.08 1.60 1.5465.8 68.4 67.2 66.6 66.8 66.2 83.6 71.1 59.1 71.1Os