Moisturization regime and implementation of chornozem agropotential under climate changes in the central Forest-Steppe

Abstract

The aim of the study. To demonstrate the main regularities in the formation of moisturization regime and to determine the impact on the implementation of agropotential and restoration of fertility of chornozem under the effect of crop rotations, fertilization, and tillage in conditions of current climate changes in the central Forest-Steppe. Methods of studies. Field method (to select samples in the depth of chornozem in different study periods), laboratory method (for thermogravimetric determination of the productive moisture reserves during the study period), mathematical, statistical, and comparative evaluative methods (to substantiate the reliability of the obtained moisture reserves in soil and elaboration of statistical models of interactions). Results of studies. On average, in 75 years of observations, the average moisture reserves in a one-meter-deep layer were 61.6 mm in November, and 51.5 mm by the median, that tended to the lower typical value which demonstrated a decrease in autumn moisture reserves. The oscillation coefficients (Коs) and Кvar were 40% and 54.4%. The moisture reserves in April, on average and by the median value, were 156–155 mm at Коs=37% and Кvar=10.3%. The average accumulation of moisture in the one-meter-deep layer in the cold period of the year was 94 mm with the median value of 99 mm, which tended more to the higher typical value (L0.75) at Коs=98% at Кvar=25.3%. In July, the moisture reserves in the one-meter-deep layer were 50.1 mm and by the median value — 45.5 mm which demonstrated tending to the lower typical value (L0.25) and the intensification of drought conditions, when the index of moisturization (Im) was within 0.77–0.88 (weakly arid conditions), and at the maximal typical value of Im=1.13–1.22 (wet conditions) at Кos=65% and Кvar=18.6%. The average loss of moisture from soil in April–July was –105 mm, which corresponded to the median value and tended to the higher typical values of losses (–108...–122 mm) at Кos=33% and Кvar=9.3%, which is a stabilized loss, tending to increase. Between the parameters of productive moisture content and climate indices, there were direct and indirect correlational relations of high correlation rate (R=±0.61–0.95±0.02, R2=37–0.90), and the relations between Im and Dm increased to strong correlation (R=±0.68–0.96±0.03, R2=0.46–0.65). It was found that in the 0–30 cm layer of podzolic chornozem, the average humus content after crop rotation with plowing was 2.34%, under surface tillage, the humus content increased by 0.15% (10 years of surface tillage), and in case of Nо-till, the humus content increased by 0.07–0.08%. In the crop rotation on typical chornozem, the average reserves of С–СО2 in the 0–30 cm layer of chornozem were 273 t/ha, and in the 0–20 cm soil layer — 182 t/ha. The average reserves of С–СО2 under No-till were 19.8 t/ha higher compared to plowing, and the reserves of С–СО2 in the 0–30 cm layer of soil started from 296 t/ha, which was 21–23 t/ha higher compared to plowing. Under surface tillage, the average reserves of С–СО2 were 14 t/ha higher than under plowing. The reserves of sequestered С–СО2 in the 0–30 cm layer corresponded to the interval of values of 285–300 t/ha and was higher than under plowing but tended to decrease compared to No- till. The reserves of С–СО 2 in the 0–20 cm chornozem layer were at the level of the median values (202.5 t/ha) and exceeded the reserves of carbon oxide under plowing by 21 t/ha, which demonstrated the increase in the sequestered ability of the 0–20 cm layer under surface tillage or No-till. In modern climatic conditions, the agropotential of chornozem is maximally implemented in the central Forest-Steppe, and a type of crop rotation is a relevant factor in increasing agrocenosis performance. In a crop rotation with peas, saturated with cereals by 80%, including 40% of grain corn, the yield of cereals was 5.56–6.15 t/ha, which exceeded the crop rotation with perennial grasses and 20% corn 1.06–1.05 times, and the yield of cereals — 1.31–1.4 times. The content of digestible protein was 0.67 t/ha or 19.7% higher in the crop rotation with grasses. Long-term (10 years) ap- plication of 8–10 cm surface tillage in a cereal crop rotation ensured the yield of cereals at the plowing level, whereas in case of No-till for 5 years, the yield of cereals was considerably lower compared to plowing and surface tillage. Conclusions. The relation, determined between climate parameters and the response of a one- meter-deep chornozem layer in the form of normalized parameters of productive moisture reserves, allows for parameterizing the moisturization regime within the periodic washing water regime of the central Forest-Steppe of Ukraine. The analysis of weather and climate parameters in the complex with the formation of productive moisture reserves in one-meter-deep layer in spring and summer periods in 1947–2022 demonstrated that in the central part of the Left-Bank Forest-Steppe, water regime is formed which corresponds to the periodically washing type, but in terms of the moisturization regime (time-wise), there is a clear stable tendency towards the manifestation of features of non-washing water regime, which mostly indicates the aridization of soil conditions for the vegetation of crops in modern conditions of global climate change in the Forest-Steppe zone. Therefore, the typization of moisture change in the one-meter-deep chornozem layer in the seasonal cycle (moisturization regime) can be used as an indicator of response to synoptic changes within climatic factors in the formation of the periodic washing regime of the central Forest-Steppe of Ukraine in modern climatic conditions.