Abstract
Soil humus degradation strengthens nutrient mining, especially phosphorus. This study was carried out on the Ukrainian Forest-Steppe Zone (UFSZ). A total of 21 soil profiles have been investigated: 11 Phaeozems, 6 Luvisols, and 4 Chernozems. Soils were tested for particle size distribution, calcium carbonate (CC), pH, and organic carbon (Corg). The evaluation of humus degradation as a reason of P depletion was performed based on indicators such as Humus Stock Gap (HSG), Humus Stability Index (S), and Yield Gap/Gain (YG/G). In order to evaluate the degree of P depletion, total phosphorus (Ptot) and its five fractions: water soluble – PH2O, exchangeable – PEX, bound to Fe and Al – PFe/Al, bound to Ca – PCa, and residual P – Pres, have been determined.Data revealed that in 14 of 21 investigated soils, S indices were below the threshold its value of nine, considered as the balanced content of humus with respect to soil texture. Next, in 11 of 21 cases, the negative humus balance indicates the yield gap in Phaeozems and Chernozems. The first three P pools (PH2O, PEX and PAl/Fe) in Phaeozems were exhausted, constituting less than 10% of the Ptot. In Phaeozems, PAl/Fe, in Luvisols, PEX, and in Chernozems, PH2O fractions were basic indicators of available P status. Their pools were directly or indirectly controlled by PCa. Humus content in Phaeozems and Chernozems revealed as the key factor impacting both total P and/or its available resources. Amelioration of P depletion requires efforts oriented on restoration of soil humus stock, concomitant with P fertilization.
Highlights
The sustainable development of the Earth is a challenge of the overriding importance for the current world population
The basic attribute of soil cover of the Ukrainian ForestSteppe Zone is the coexistence of different soil groups, which originated from loess and loess-like mineral material deposited on calcium carbonate bedrock
In 11 of 21 cases, the humus stock balance can be considered as the index decisive for the yield gap development, especially in Phaeozems and Chernozems
Summary
The sustainable development of the Earth is a challenge of the overriding importance for the current world population. Soil organic matter is the core of soil fertility, a factor decisive for water and nutrient supply to growing plants, including crops It is well recognized, that any change in land use from natural to arable may lead to a drastic decrease in the humus content. As reported by Wu et al [6], the annual loss of organic carbon (OC) from a calcareous soil developed from loess (Calcic Kastanozems, FAO; the Loess Plateau, China) over 42 years of cultivation ranged from 0.96 to 1.06 t ha−1 According to these Authors, the native level of OC content can be restored provided the application of manure or straw in combination with nitrogen and phosphorus
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