Tillage Techniques That Can Save Moisture
DS-4-97, June 1997
Dave Franzen, NDSU Extension Soil Specialist
Moisture is the single most limiting factor to crop yields in North Dakota. Tillage techniques that conserve moisture are important to increasing crop yields and limiting the devastating consequences of drought. Soil holds moisture mostly on the basis of texture, although plant available water can be modified by soil organic matter content because of the way soil particles aggregate. A silt loam soil holds the greatest amount of water (Table 1), while a sand holds the least. In dry years, the amount of moisture held in the soil is crucial to final yield. In North Dakota, about 5 inches of water is needed to produce some kind of a crop. Each additional inch of moisture translates into about 2.5-3 bu/acre more wheat, 4.5-5.5 bu/acre more corn or 200-300 lb/acre more sunflower seed.
| Table 1. Approximate soil moisture holding capacity of different soil textures. |
| Texture |
Moisture Holding Capacity |
| sand |
0.5-1.1 (inches/foot) |
| sandy loam |
1.1-1.8 (inches/foot) |
| loam |
1.6-2.2 (inches/foot) |
| silt loam |
2.0-2.8 (inches/foot) |
| clay loam |
1.7-2.5 (inches/foot) |
TillageTillage has been the traditional way to prepare seedbeds and control weeds. To conserve moisture, the kind of tillage and the number of tillage operations affects the amount of moisture remaining following tillage and the ability of the soil surface to attract and store additional moisture (Table 2).
| Table 2. Moisture loss with tillage over four days. |
| Tillage implement |
Inches of Moisture Loss |
| Disc |
0.52 (inches) |
| Chisel |
0.50 (inches) |
| Sweep plow |
0.14 (inches) |
| Rodweeder |
0.22 (inches) |
The greatest moisture loss is usually experienced during the first field trip. However, additional trips result in more extensive drying in the tillage zone. Moisture loss from tillage is especially important during dry springs, when the seedbed may dry out and result in poor germination if rainfall does not rewet the seed zone. Spring tillage should be shallow to limit moisture loss and allow planting in moist soil. Conserving spring moisture to allow seed germination is especially difficult with small seeded crops like canola and in dry windy conditions. Use of a packer or harrow to fill in and seal the ground during the tillage operation may be important.
Fall tillage influences the amount of snow catch, which is important in many years to help recharge soil moisture after a previously dry summer and fall. Snow catch is influenced by surface roughness, but mostly by stubble height. Conservation tillage, and especially no-till increases the amount of stubble left on the surface (Table 3).
| Table 3. Influence of tillage on residue cover. |
| Operation |
% Residue Remaining |
| No-till |
100 |
| Undercutter |
70-90 |
| Chisel plow w/sweeps |
50-80 |
| Chisel plow w/straight spikes |
40-70 |
| Chisel plow w/twisted spikes |
20-50 |
| Disc (tandem or offset) |
|
| blades less than 23 in. diameter |
40-70 |
| blades 23 to 28 in. diameter |
20-50 |
| blades greater than 23 in. diameter |
10-40 |
| Field cultivator |
40-70 |
| Moldboard plow |
0-10 |
North Dakota research has shown that leaving stubble and stubble height are especially important for increasing moisture over winter. The difference between leaving upright stubble and leaving no stubble made a difference of between 1.1 inches and 2.15 inches of extra moisture for the stubble treatments in a series of experiments. The studies averaged about 1.5 inches of extra moisture due to snow catch. Stubble left at 13 to 15 inches increased spring soil moisture by 1.45 inches compared to a 2 inch stubble height (Table 4).
| Table 4. Overwinter change in soil moisture content at Mandan, N.D. with different stubble heights. |
| |
Stubble Management Height, inches |
| Year |
2 |
8-10 |
13-15 |
| 1987-88 |
1.1 |
1.2 |
2.5 |
| 1988-89 |
2.0 |
3.3 |
3.5 |
| Avg. difference |
-- |
0.6 |
1.45 |
No-till or Direct SeedingNo-till seeding has many moisture conservation advantages over conservation and conventional tillage. No-till leaves the most stubble overwinter to catch snow. No-till does not require tillage before seeding and the possible loss of seedbed soil moisture. No-till stubble protects the soil moisture with a mulch cover that limits moisture losses during the growing season. No-till is practiced by many producers in North Dakota and has been a proven performer over many years. Adoption of no-till should be considered in any area where moisture conservation is important. Along with moisture conservation, no-till also reduces soil water and wind erosion, which degrade soil quality over time. Long-term no-till studies also indicate that organic matter increases over time, further increasing soil quality.
Recommendations
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Consider adoption of no-till farming. Support groups such as the Manitoba-North Dakota Zero-Tillage Farmers Association exist to help producers begin. In many cases, adoption of no-till does not require purchase of expensive equipment, but some modification of equipment is likely.
-
Use tillage implements that retain crop residues, leave a rough soil surface and limit soil drying, such as undercutters, rodweeders and sweep style cultivators.
-
Avoid tillage with implements that bury more than 50% of crop residues, such as discs with greater than 24 inch diameters, and moldboard plows.
-
Limit tillage trips.
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Perform tillage at right angles to the prevailing winds (usually north and south with a west prevailing wind).
-
Follow the contour of the land in hilly landscapes to intercept water in the event of heavy rainfall.
-
Control weeds through herbicides rather than tillage.
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