Conversion of meadow and forest ecosystems to agricultural land generally leads to changes in soil structure. This comparative study presents the composition and stability of structural aggregates in humus horizons (0-30 cm) of noncarbonate silty-clay Fluvisols in the Kolubara River Valley, W Serbia. Aggregates collected from under a native forest were compared to aggregates from meadows and arable fields which underwent crop rotation for > 100 y. The results show that size distribution and stability of structural aggregates in the humus horizons of arable soil are significantly impaired due to long-term anthropogenization. In the humus horizons, the content of the agronomically most valuable aggregates (0.25-10 mm) decreased by a factor of ≈ 2, from 68%-74% to 37%-39%, while the percentage of cloddy aggregates (>10 mm) increased by a factor of ≈ 2, from 23%-31% to 48%-62%, compared to forest aggregates. The long-term-arable soil had significantly (p < 0.05) lower aggregate stability, determined by wet sieving, than meadow and forest soils. The lowest aggregate stability was found in aggregates > 3 mm. Their content is ≈ 2.5-3 times lower in arable soil (13%-16%) than in forest soil (32%-42%) at a depth of 0-20 cm. The largest mean weight diameters of dry aggregates (dMWD) with a range between 12.6 and 14.7 mm were found in arable soil, vs. 9.5-9.9 mm in meadow and 6.5-8.3 mm in forest. The arable soil had significantly lower mean weight diameters of wet-stable aggregates (wMWD) and a lower structure coefficient (Ks) than forest and meadow soils. The dispersion ratio (DR) of arable soil was significantly higher than that of forest and meadow soils. Forest and meadow showed a significantly higher soil organic-matter content (SOM) by 74% and 39%, respectively, compared with arable soil, while meadow uses decreased the SOM content by 57% compared with forest at a depth of 0-10 cm. In conclusion, the results showed that long-term conventional tillage of soils from natural forest and meadow in the lowland ecosystems of W Serbia degraded soil aggregate-size distribution and stability and reduced SOM content, probably resulting in lower productivity and reduced crop yields.

Frequent occurrence of droughts over the last two decades, as well as increases in the air temperature increase have led to the rise farmers' concerns that field crop production would not be possible without irrigation. The aim of this research is to assess how two adaptation measures, sowing dates and irrigation and water excess impacts the yields of wheat, maize and sunflower in Serbia. In order to assess the future of climatic condition five representative locations have been selected for the analysis (Novi Sad, Valjevo, Kragujevac, Negotic and Leskovac). For the analysis of future climatic conditions, results of the ensemble of nine regional climate models from the Euro-CORDEX database were used. The period between 1986 and 2005 was used as a reference, while time slices in the future are: 2016-2035 (near future), 2046-2065 (mid-century) and 2081-2100 (end of the century). Analyses were made for the scenario of GHG emmisions RCP8.5. Aquacrop model v.6.1 was used for the yield, sowing period, and irrigation requirement assessment. The analysis and the results have indicated that earlier start of the growing season of maize and sunflower for 5, 11 and 19 days in near future, mid and end of the century, respectively, whereas optimal sowing period for rainfed wheat will vary from September 20 to November 30, depending on rainfall occurrence, and for irrigated one in optimal sowing period (beginning of October). The warmer climate will shorten the growing cycle of all studied crops. However, the shortening significantly differs among locations. The growing cycle of maize shortened from 34 up to 48 days in Valjevo in near future through the end of the century, while in Negotin it could be less only for 6 days. The increase in air temperature and earlier start of the growing season will enable the most sensitive phenophases, flowering and fruit formation, to appear in a period of more favorable weather conditions, together with the increase in CO2 concentration, can help mitigate the negative impact of the climate change, so that there will be no reduction in sunflower yields. Slight increment of sunflower yields could be expected by the end of century (2.3 - 13.8%), whereas yield of maize will remain on the present level. The increase of wheat yield could be expected only in the near future (up to 8.3 %), but also it can be reduced at some locations by the end of the century. Irrigation water requirements of all studied crops will remain at the same level the same level as the present, but only if sowing applied in the optimal period. Although it is known that irrigation changes microclimatic conditions, ie., the air humidity increases, and the air temperature decreases (the so-called oasis effect), which can affect the extension of the vegetation period, and thus the increase in yield. Such subtle changes in the microclimate cannot be "recognized" by models, so even simulated yields cannot be fully (accurately) predicted. This research come to the conclusion that in addition to irrigation, shifting the sowing dates earlier can have an impact on mitigating the consequences of climate change in crop production, which is of great importance for areas where there is not enough water for irrigation. The risk of drought will exist on shallow and sandy soils as well as on overwetted lands that cannot be plowed until drained to be sown in optimal terms and all crops sown in the late spring.

SažetakPrirodno snabdevanje vodom retko ispunjavaju potrebe useva za vodom, stoga navodnjavanje ima veliku ulogu u osiguranju visokih i kvalitetnih prinosa. Da bi navodnjavanje bilo isplativo, neophodno je obezbediti efikasno korišćenje vode. Cilj ovog rada je da se utvrdi efikasnost korišćenja vode (EKV) važnijih ratarskih kultura u uslovima sa i bez navodnjavanja. Podaci o potrošnji vode i prinosa su preuzeta iz naučnih publikacija. Analiza EKV na području Srbije pokazuju da se uglavnom postiže pun genetski potencijal u uslovima dobre snabdevenosti vodom. Prinos nekih kultura direktno zavisi od raspoložive količine vode kao što su: lucerka, kukuruz i soja, dok se kod nekih useva takva veza ne može uočiti. Efekat navodnjavanja razlikuje se po godinama, ali ne isključivo od količine i rasporeda padavina. To ukazuje da EKV zavisi i od drugih faktora, kao što su ekstremne temperature, mraz, grad, snabdevenost hranivima i zdravstvenog stanja biljaka.Ključne reči: prinosi, potrošnja vode, ratarske kulture

SažetakU ovom radu prikazani su rezultati merenja temerature nadzemnog dela biljaka paprike i paradajza primenom termovizijske kamere sa ciljem određivanja uticaja mulč folije na temperaturu biljnog pokrivača. Ogled je postavljen na otvorenom polju na zemljištu tipa karbonatni černozem u Staroj Pazovi (40 km severno od Beograda, Srbija), a merenja temperature izvedena u periodu maj-septembar 2012. Kod paprike su praćene tri varijante režima navodnjavanja sa i bez mulč folije. Varijanta sa punim navodnjavanjem (F) kada je pokriveno 100 % ETc (evapotranspiracije kulture), varijanta sa redukovanim navodnjavanjem (R) kada je pokriveno 80% ETc i varijanta sa redukovanim navodnjavanjem (S) kada je pokriveno 70% ETc. Kod paradajza su praćene dve varijante režima zalivanja, varijanta sa punim navodnjavanjem, (F) kada je pokriveno 100 % ETc i varijanta sa redukovanim navodnjavanjem (S) kada je pokriveno 50% ETc sa i bez primene mulč folije. Merenja temperature biljaka izvedena su termovizijskom kamerom (FLIR, T335) četiri puta u toku vegetacije paprike i šest puta u toku vegetacije paradajza. Sa svake varijante je uzet uzorak od 15 temperatura na osnovu kojih je merena prosečna temperatura biljaka na svakoj varijanti navodnjavanja. Podaci merenja temperatura nadzemnog dela paprike pokazuju, da je temperatura biljnog pokrivača bila niža na svim varijantama gde je postavljena mulč folija. Biljke paprike na F, R, S varijantama sa mulč folijom bile su hladnije od biljaka na istim varijantama zalivanja bez mulč folije prosečno za 1,45°C, 1,52°C, 1,38°C, respektivno. Kod paradajza razlike su manje u odnosu na papriku. Na F varijanti sa mulč folijom biljke su bile prosečno za 0.3 °C hladnije od biljaka na F varijanti bez folije. Na varijanti redukovanog zalivanja (S), temperatura biljaka paradajza sa mulč folijom je prosečno za 1°C niža od temperature biljaka bez folije. Rezultati merenja pokazuju da postoji značajan uticaj mulč folije na temperaturu biljnog pokrivača paprike, a u manjoj meri kod paradajza. Mulč folija umanjuje evaporaciju, biljke imaju na raspolaganju više vode, intenzivnija je transpiracija, pa je zagrevanje biljke manje. Paradajz je biljka gušćeg sklopa kod koje razvijena biomasa utiče na smanjenje evaporacije u odnosu na otkriveno zemljište, pa je uticaj folije manje izražen.