engleski

Efficiency of Mineral Nitrogen Rates Applied in Maize Fertilization

Introduction. Intensive application of mineral fertilizers in the last decades has caused numerous changes to the environment. Judging by the data presented in the Danube Environmental Study, the Danube River basin includes many areas with more or less intensive agriculture. A more rational application of mineral nitrogen throughout the region requires scientific research programmes to be made and implemented, and then used as a basis for educating farmers about the ecologically most acceptable ways of applying mineral fertilizers. Material and method. With the aim of determining the sustainable mineral nitrogen rates for fertilization of major field crops in central Croatia, a stationary field trial with 10 treatments in 4 replications was set up in the "heart" of the Lonja Field (Lonjsko polje). In the first investigation year (1996) maize was grown as test crop on the trial area. Water leached through the soil to a 80 cm depth was caught by the installed lysimeters. The lysimeters applied were without lateral sides (after Ebermayer). The trial included the following treatments: 1. Check, 2. N0 PK, 3. N100 PK, 4. N150 PK, 5. N200 PK, 6. N250 PK, 7. N250 PK + Phosphogypsum, 8. N250 PK+Zeolite tuff+CaCO3, 9. N300PK, and 10. Black fallow. The trial plot size was 30x130 m (3900 m2). Maize fertilization was carried out with 600 kg/ha NPK 7-20-30, which amounts to 42 kg nitrogen, 120 kg phosphorus and 180 kg potassium. In the N0PK treatment, mineral fertilizers without nitrogen were applied. Of the total nitrogen quantity, 60% was applied before the planting while the remaining 40% in two topdressings of 20% of total nitrogen quantity each. Phosphogypsum (12 t/ha) and zeolite tuff with CaCO3 (3 t/ha) were applied prior to the basic soil tillage. In the treatment involving black fallow, all tillage practices were the same as in other trial treatments, including also supplementary tillage practices. Maize (hybrid ETA 272) was sown on 18 May (population density 77000 plants/ha). The nitrate content was determined in samples of soil, lysimeter water (Cadmium reduction method) and plant material. Mineral nitrogen utilization is shown in terms of maize grain yields and the amount of mineral nitrogen applied, as well as the results of chemical analyses for nitrogen content. Results and discussion. The trial is highly significant with regard to maize yields (Table 1). As expected, the lowest yield was recorded in the check variant. Most probably owing to the existing amounts of available phosphorus and potassium in the soil, fertilization with mineral phosphorus and potassium fertilizers had almost no influence on the increase of maize yield. This conclusion is based on the difference between the check variant yield and the yield obtained in the treatment with phosphorus and potassium, but without nitrogen. The treatment with 100 kg N rendered a statistically significant yield increase, both relative to the check variant and the variant with phosphorus and potassium without nitrogen. A further yield increase was recorded in the treatment with 150 kg N, but not above that quantity. In fact, more or less equal yields, or at least in the same significance range, were achieved with 150, 200, 250 and 300 kg of nitrogen. The depressive impact of phosphogypsum on the yield of maize grain is noticeable, as well as the absence of effects of the special natural, zeolite-based, substratum. The results point to the conclusion that the nitrogen rate of 150 kg N resulted in a relatively high yield of maize grain, particularly considering the fact that the hybrid in question has a short growing season. The trial is significant also with regard to the maize grain nitrogen content. On the basis of maize yield and grain nitrogen content, the amount of nitrogen removed with the yield was calculated. This provided the basic data for a simplified presentation of nitrogen balance per different trial treatments. A total amount of 485.2 mm of rainfall was recorded between maize planting and the last evacuation of lysimeters. The average water quantity in lysimeters was 38.0 l, or 15.7%. The fact that this is the warm part of the year, marked also by high evaporation, the several-year average of which shows no water surplus, points to the conclusion that the distribution and intensity of rainfall in July, August and September 1996 were decisive for the filling of lysimeters with unexpectedly large quantities of water. The highest total nitrogen loss of 47.5 kg/ha NO3- N was recorded in the treatment with phosphogypsum. Table 1 - Yield of maize grain, dt/ha, grain nitrogen content, nitrogen removed with maize yield and nitrogen leached with lysimeter water Trial treatment Yield, dt/ha % N N removed, kg/ha NO3 N leached, kg/ha 1. Check 58.27 1.15 66.9 3.7 2. N0 PK 58.90 1.30 76.6 9.6 3. N100 PK 76.76 1.41 108.0 2.5 4. N150 PK 91.18 1.54 140.4 1.4 5. N200 PK 91.78 1.67 153.3 15.9 6. N250 PK 91.56 1.63 148.8 20.0 7. N250 PK+PG 78.79 1.72 135.5 47.5 8. N250 PK+Z+CaCO3 86.99 1.69 146.6 17.7 9. N300 PK 88.85 1.73 153.7 17.7 10. Black fallow - - - 3.3 LSD = 5% 12.40 0.17 LSD = 1% 16.90 0.23 The relation between particular trial treatments with regard to the mineral nitrogen rates applied, nitrogen leached into lysimeters, and nitrogen removed with maize yield is shown in fig. 1. Figure 1 - Relation between the nitrogen applied, leached into lysimeters, and removed with maize yield (kg/ha) In comparison with nitrogen losses in the other two treatments with 250 kg of mineral nitrogen, even that with 300 kg, the nitrogen losses through leaching in the treatment involving phosphogypsum were twice larger. The lowest quantity of leached nitrogen was recorded in treatment 4 with 150 kg mineral nitrogen, which was followed by treatment 3 - 100 kg N, and only then treatment 10 - black fallow, and the check treatment. Such phosphogypsum effects can be attributed to its action upon the chemical and physical properties of the soil. Conclusion. According to the results of the first investigation year, the sustainable mineral fertilizer rate for maize in the given agroecological conditions ranges between 100 and 150 kg /ha of mineral nitrogen.

nitrogen; maize; fertilization

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