Effect of nitrogen fertilizer on growth of seeded grassland dry biomass in process of deposol: Biological reclamation

The paper presents the results of a three-year trial (2011-2013) on the variability of the yield of dry overhead biomass of the seeding grassland depending on the application of N fertilizer.Three grass-leguminous mixtures and one grass mixture has been researched (total of ten species of grass and leguminose) in the process of the biological phase of the reclamation of the technogenic soil, the type of Deposol. The research has been conducted on the Deposol at internal disposal area for overburden from Raskovac open pit in Stanari coal mine(Republic of Srpska, Bosnia and Herzegovina).The seeded grasslands stand for the significant driving force of pedogenetic processes in new soil reclamation. There are four treatments of doses of N fertilizers in application (N1 144, N2114, N3100 and N4130kg/ha). N fertilizer is used in basic and supplemented grassland nutrition. The application of N fertilizer in the seeded grassland has shown significant variation of dry biomass. The results have varied by years, different compositions and particular cuttings. In 2011 the N effect was lower in the first than in the second cutting. In 2012 and 2013 the N effect was better in the first cutting. The highest effect of N fertilizer is found with the TDS-3 mixture in every research year ( x 1 kg N = 36.32 kg in 2011, x 1 kg N = 97.67 kg in 2012 and x 1 kg N = 115.93 kg of biomass in 2013). The highest effect of 1 kg N on the biomass yield is calculated at TDS mixture at N3 treatment in the first cutting in 2013 (190.12). The lowest effect of 1 kg N on the biomass yield is calculated at the TDS-1 composition at treatment N3 in the first cutting in 2011 (10.00). The better effect is achieved with the smaller dose of N fertilizer. This is the starting point in any future standardization of fertilizers when fertilizing the seeded grasslands in the process of Deposol reclamation.


INTRODUCTION
Development of plant cover and mineralization of plant residues affect the process of formation of technogenic soils and accumulation of organic carbon at the soil surfaces in the reclamation process. On the other hand, the growth of plants and mineralization are mostly limited by the Original paper doi:10.5937/ZemBilj1902012M 13 absence of N and P (Liendemann et al., 1989;Vimmerstedt et al., 1989;Stojanović et al., 1977).
The vegetation plays significant role in reclamation when it comes to the prevention of newly formed technogenic soils from erosion providing the accumulation of fine soil matters (Tordoff et al., 2000;Conesa et al., 2007).
The task of seeded grasslands establishment (by seeding the grass-legume mixtures) is to decrease the intensity of water erosions, begin the formation of fertile technogenic soil surface layer followed by usage of over-ground biomass as bulky cattle food. The success of establishment of seeded grasslands depends on proper selection of species and genotypes of grass and legumes since the combination of these two gives best results (Kessler and Lehman, 1998). Burger et al. (2009) gives the example for composition of one grass-legume mixture for deposal reclamation (with pH 5.0-6.5, ie. forest conditions) as it follows: Lolium italicum A.
Growth of green and dry mass at the established grasslands greatly depends on fertilizers and methods of application (Stošić et al., 2004). The grasslands seeded without applying any fertilizers rapidly deteriorate; the growth may lack already in the first year, especially if there are no legumes applied. The goal with seeded grasslands is to support leguminous component to its maximum so to reduce nitrogen fertilizers and improve the quality of plants in later application.
According to Dublјević (2007), in his research activities, recorded the highest participation of grasses with the biggest doses of N fertilizer, and legumes and other plants with smallest doses of fertilizers.
When researching the mountain grasslands in Macedonia, Prentović et al. (2007), recorded 0.27 t ha -1 of hay production with its maximum of 1.7 t ha -1 when treated with 80 kg ha -1 of N.
The highest effects of N fertilizer on growth is achieved when 50 kg ha -1 of N is applied. Vučković et al. (2007), in their two-year research on effects of mineral fertilizers on growth of green and dry mass at Agrostietum vulgaris grassland (Pavlović, 1955)  According to Stošić (1990), the research of effects of fertilizers on the growth of these mixtures on Kopaonik in the first and second year, the growth of dry mass is better at the places where the dose of 80 kg ha -1 P2O5 and K2О (2.86 and 9.05 t ha -1 ) fertilizer is applied. The growth is slower (1.74 and 8.87 t ha -1 ) with the 80 kg ha -1 N, P2O5 and K2О due to the effects of N on high grasses that suppress Trifolium prаtense L.
The results of recent physical and chemical analysis of Deposol at the overburden landfills at the mine in Stanari indicated good physical-mechanical but poor chemical properties (Malić, 2015;Malić and Marković, 2012;Malić, 2010).
The goal of research is to analyze the effects of N fertilizer on production properties, i.e.
dry mass of grass-legume mixture, at the seeded grasslands in the process of soil reclamation.

MATERIAL AND METHODS
The coal basin Stanari is located between 44°40' and 44°50'N and 17°45' and 18°00'E, in the The standard for seeding is 45 kg ha -1 . Treated Deposol was subject to seeding.
Fertilization with mineral fertilizers NPK 15:15:15 in two doses: 90 and 60 kg ha -1 N (pure nutrients) was performed in pre-seeding phase. The N fertilizer KAN (27% N) was applied in two nutrition treatments with two doses in the second and third year of research (54 and 40 kg ha -1 N of pure nutrient). First dose was applied at the initial vegetation stage. The second dose was applied on the tenth day after mowing the first cutting. The grassland was mowed by mulching machine twice a year leaving the plants at the Deposol surface in the process of reclamation.
The obtained results were examined by analysis of variance (ANOVA). The significance of the differences between the basic factors and their interactions was tested with the F-test, while the differences between mean values determined by the LSD test.  The basic climate indicators (precipitation and air temperature) within the three-year experimental period are shown in climate diagram ( for both cuts. In the first year, for the first cutting, N is calculated out of NPK fertilizer applied in seeding, since the first nutrition is not applied while the second nutrition is applied. The calculation for the second and third year of research is made on the grounds of N from treatment (first and second nutrition treatment).    The effects of total quantities of nutrition from fertilizers through the effect of application of pure N on the values of dry biomass production yielded much different results. Comparing the results Original paper doi:10.5937/ZemBilj1902012M 19 by years, the lowest effect was achieved in 2011 with all mixtures. This is direct consequence of soil moisture deficit in the entire vegetation period. In 2011, the effect of N is lower in the first than in the second cutting, even though the first cutting had bigger growing ratio due to the participation of weed in total biomass (Malić, 2015).
The highest effect of 1 kg of N on dry mass production in the first cutting (of 7,700 kg/ha)   -in the production of dry biomass in the first cutting, the highest average value is recorded with the TDS-3 mixture (2.5 t/ha and 4.5 t/ha) in the initial two years of research and TDS-1 mixture (6.8 t/ha) in the third year; -the lowest average growth in the first year recoreded with TDS-1 mixture (1.4 t/ha) and the lowest average growth in the following two years with TDS-4 (3.9 t/ha and 5.2 t/ha); -the biggest average growth of dry biomass in the second cutting in the first year of research is recorded with the TDS-1 mixture (2.2 t/ha), and the biggest average values of 4.6 and 3.9 t/ha are recorded with TDS-3 mixture in the following two years; -the lowest average values are recorded with the TDS-4 mixture (1.6 t/ha and 2.9 t/ha) in the initial two years of research and with the TS-2 mixture (3.0 t/ha) in the last year;