Impact of the Water Regime of Peat-Gley Soils on Crop Productivity (1982)

Investigations into crop response to soil water regimes on drained peatlands have demonstrated the absolute necessity of two-way drainage-subirrigation systems. Previous research established that perennial grasses are the most demanding regarding optimal soil moisture, followed by potatoes and cereal grains [1]. However, a rigorous comparative evaluation of optimization efficiency across different crop types has been lacking, complicating the engineering and economic rationale for dual-action reclamation networks.

Field Experimental Methods and Soil Conditions

During 1976–1980 at the Polesian Experimental Land Reclamation Station (Brest Region), we investigated the productivity of timothy grass (Phleum pratense), spring barley, and potatoes as a function of plough layer moisture dynamics on peat-gley soils.

In field trials, drought stress was artificially simulated across one set of plots by shielding them from natural precipitation throughout the vegetative season (May to September) using lightweight mobile shelters. In this variant, plant water uptake depended exclusively on spring moisture reserves and capillary rise from the water table. In a second variant, supplemental sprinkler irrigation maintained plough layer moisture within an optimal range (not below 70% of field capacity). These treatments were evaluated against control plots subject to ambient rainfed and groundwater regimes.

Groundwater levels (GWL) were uniform across all treatments, averaging depths of 87, 79, 97, 77, and 76 cm across respective experimental years.

When precipitation was excluded, these groundwater depths proved insufficient to support perennial grasses: by late May, soil moisture beneath timothy grass fell below the threshold of biological availability (30% by soil volume). This pattern recurred consistently across all trial seasons.

Consequently, with water tables exceeding 75 cm depth, atmospheric precipitation serves as an indispensable moisture source for forage swards. Regarding precipitation distribution during the early growing season (May–July, corresponding to the barley vegetative cycle), two seasons (1977 and 1980) were exceptionally wet, two (1976 and 1979) were sharply arid, and 1978 approximated the long-term climatic norm.

Plough Horizon Moisture Dynamics

Moisture dynamics in the topsoil horizon beneath cereal crops varied markedly across climatic cycles and water regulation regimes (Table 1).

Owing to the physiological phenology of potato crops, soil moisture depletion beneath tubers commenced considerably later in the season (late June) compared to barley.

Crop Differential Response to Water Management

1. Perennial Forage Grasses (Timothy Grass)

Our trials revealed pronounced divergence in crop physiological response. Timothy grass proved exceptionally vulnerable to water deficits.

Under simulated drought (exclusion of rain with GWL below 75 cm), timothy hay yield suffered a catastrophic 2–4 fold collapse (dropping to 13–22 cwt/ha), and the grass sward completely failed by year three. Maintaining topsoil moisture via sprinkler irrigation at 45–55% maintained high productivity, reaching 104–113 cwt/ha.

Climatological records across Polesia [3] demonstrate that only 28% of summer vegetative cycles provide sufficient natural rainfall. Hence, in more than two out of three years, perennial grasses on drained peatlands suffer severe moisture deficits and demand active water regulation.

2. Cereal Crops (Barley) and Potatoes

In striking contrast, spring barley exhibited an inverse relationship between precipitation and final grain productivity (Table 3).

Peak barley yields (60.2–64.0 cwt/ha) occurred during dry, sunny seasons characterized by intense solar insolation. In rainy seasons, grain yield fell nearly twofold to 36.4–37.3 cwt/ha, regardless of supplemental irrigation.

This demonstrates that interannual grain yield variation on peat soils is governed not primarily by soil water deficits, but by overcast weather conditions: reduced photosynthetically active radiation (PAR), high atmospheric humidity, and soil cooling [4, 5]. Sprinkler irrigation for barley is economically justified only when precipitation during active vegetative growth falls below 87% of normal (occurring in Polesia approximately once every 3–4 years).

Potatoes proved exceptionally sensitive to soil waterlogging and impaired rhizosphere aeration. In wet years, tuber yield declined from 410–525 down to 253–260 cwt/ha. Rain exclusion during wet years paradoxically improved tuber yields by preventing anoxia in the root zone.

Theoretical Conclusions and the Guaranteed Technological Baseline

Synthesis of the five-year experimental data establishes key principles for agricultural land reclamation:

1. Crop-Specific Asymmetry: Water regulation on drained peat-gley soils completely prevents forage failures and ensures high, stable yields of perennial grasses, but cannot stabilize cereal or potato yields at their peak potential.
2. Guaranteed Technological Baseline: Controlled water-table management eliminating both root-zone drought and anaerobic saturation ensures a guaranteed minimum yield threshold — not less than 37 cwt/ha of barley grain and 210 cwt/ha of potato tubers under any adverse meteorological conditions.
3. Climatic Ceilings: Yield gains beyond this baseline (up to 64 cwt/ha for barley and 525 cwt/ha for potatoes) depend on solar radiation and cumulative thermal energy — macroclimatic variables that remain beyond direct field engineering control.

References

1. Afanasik, G. I., Shaban, N. S., Piatnitski, V. N., Tribis, V. P. Integrated Regulation of Plant Life Conditions on Peat Soils. — Minsk: Uradzhay, 1980. — 136 p.
2. Ivitsky, A. I., Afanasik, G. I., Mikhaltsevich, A. I. Design and Engineering of Regulatory Networks for Drainage-Subirrigation Systems on Peat Soils. — Minsk: Uradzhay, 1979. — 80 p.
3. Kushnir, N. V., Zhilin, V. E., Lundin, K. P. Precipitation Regime and Air Temperature on Drained Peatlands // Land Reclamation of Waterlogged Lands. Vol. XXV. — Minsk: Uradzhay, 1977. — Pp. 78–86.
4. Features of the Growth Physiology of Cereal Crops on Peat Soil. — Minsk: Nauka i Tekhnika, 1970. — 263 p.
5. Kozłowska-Ptaszyńska, Z., Głażewski, S. Size and Lifespan of Assimilatory Surface and Photosynthetic Intensity in Winter Wheat Varieties Relative to Nitrogen Fertilization Levels // Pamiętnik Puławski. — 1975. — No. 64. — Pp. 135–147.