FAQs - DRYLAND CROPPING SYSTEMS
Q: What is dryland farming?
A: Dryland farming systems do not use irrigation but depend on precipitation to meet crop requirements. For this reason, it is essential that the producer first evaluate the effect of conversion from irrigated to dryland farming based on crop yields, crop production costs, and farm profits from neighbors in similar geographical and climatic contexts in order to assess associated risks. This assessment will help the producer determine how much of their land to transfer and its feasibility in relation to type of crop, crop yield, production costs, and total potential profit. The most common dryland crops are pasture and small grains, however, row crops such as sorghum, corn, or cotton may also withstand dryland farming depending on geographical location. Record keeping will help the producer monitor changes over time in order to assess long term risk and economic feasibility.
Q: What crops are tolerant to limited moisture and how do they achieve more efficient water use?
A: Climate, elevation, season, and market are four determining factors that dictate which crops to plant and when. Depending on the soil conditions and precipitation, some crops are drought and saline tolerant while others may flourish in a cooler or warmer climate. Pasture is a good example of this, where warm-season grasses perform better in Texas while cool-season fescue grows better in high altitude and cool temperatures. One of the best ways to manage water resources is by choosing specific plants for specific eco-agro purposes and by appropriate plant rotation such as planting and interchanging crops at specific times in order to improve soil moisture, nitrogen fixation, and reduce soil erosion.
Cool-season, short-growth crops such as brown mustard, canola and camelina have become an useful component in on-farm agricultural water conservation strategies. They are known to use less water and allow more time to accumulate water prior to planting wheat, for example, to replace fallow in the High Plains of western United States. Choosing crops based on their plant-water requirements as well as crop rotation and fallow periods contribute to agricultural water conservation at the micro and macro level of farming systems.
Q: What are some dryland cropping system practices that contribute to water conservation?
A: Reduced, minimum, and no-tillage planting systems have all been proven to be effective ways to conserve water under dryland cropping conditions. It is generally agreed among agronomists, soil scientists, and dryland cropping systems specialists that each tillage or land disturbance operation associated with dryland cropping results in a moisture loss to evaporation of as much as ½” equivalent depth. This amount of moisture translates to 13,000 to 14,000 gallons of water per acre.
Q: What are the key concepts for water conservation practices in non-irrigated (dryland) cropping situations?
A: As little as 17% of precipitation that falls in dryland systems actually gets used by the crop. So the question is, "what happens to the rest of the precipitation?" Precipitation is 'lost' for crop use because it is intercepted by the crop or other vegetation, runs off from the soil surface to another location, evaporates from soil or other surfaces without entering the crop root zone, percolates below the crop root zone, or is transpired by weeds or other non-crop plants. Water conservation practices are designed to eliminate or minimize these 'losses' to conserve precipitation in the crop root zone for crop use. However, it is important to note that although these are 'losses' to the cropping system, the lost water is not lost from the system as a whole and the water may be beneficially used by the crop or ecosystem elsewhere. For example, water runoff may be captured somewhere else in the field for crop use or contribute to a watershed's yield. Likewise, deep percolation can recharge groundwater for other uses as well.
Q: What are the major differences in water conservation practices between irrigated and non-irrigated (dryland) situations?
A: The primary difference is that with dryland situations, the land manager does not have the capability of controlling the timing, intensity and amount of water reaching the soil surface as it arrives through natural precipitation. Thus, the importance of capturing and storing as much precipitation as possible is much higher under dryland cropping.
Q: What are some similarities in water conservation practices between irrigated and non-irrigated (dryland) situations?
A: With both dryland and irrigated situations, water conservation is enhanced when the land manager can efficiently capture and store water from precipitation and/or irrigation in the crop rootzone. This involves practices that enhance infiltration and reduce runoff and evaporation. These are described more in detail below.
Q: How do tillage practices affect water conservation in dryland production systems?
A: Tillage practices are a key factor to water conservation in dryland production systems. Every tillage event will increase soil surface evaporation as the generally wetter soil is exposed to the sun and wind. Capture and storage of precipitation is maximized when conservation tillage is practiced. Other tillage practices that aid in capture and storage of precipitation include contour farming – leaving furrows perpendicular to the slope; tillage practices that roughen the soil surface to capture snow; and tillage implements that leave small storage basins or pockets to temporarily store water for infiltration during precipitation events reducing runoff. These practices have some limitations under high intensity precipitation events and in sloped fields.
Q: What is conservation tillage?
A: Conservation tillage, by definition, is any tillage system that leaves at least 30% of crop residue covering the soil surface. However, this is the minimum amount of residue generally considered to reduce soil erosion to acceptable levels. To reduce significantly reduce surface evaporation, 50% of crop residue cover is generally considered necessary.
Q: How does crop residue enhance water conservation under dryland cropping systems?
A: Crop residue performs a multitude of functions for water conservation: First it protects the soil surface from sealing caused by raindrop impact; it can provided small pockets or dams of crop residue to provide temporary water reservoirs during precipitation events; it captures snow – particularly effective with standing crop residue; and it reduces evaporation by shading the soil surface from the sun and reducing the wind velocity at the soil surface.
Q: How important is weed control under dryland cropping systems?
A: In any cropping situation, weeds compete with the crop for space, light, nutrients and most importantly water. Therefore, excellent weed control during both the cropping season and a fallow period is critical to maximizing the amount of water available for the crop.
Q: What is the difference between the terms no-tillage, minimum tillage, conservation tillage, and stubble mulch tillage?
A: All of these definitions have some variability in their use, particularly in the field. No-tillage is a somewhat deceiving term in that some tillage or soil disturbance has to happen during the planting operation to allow the planter to move through the crop residue and provide adequate soil to seed contact. However, no-till generally means that soil and residue disturbance only occurs during the planting operation and this disturbance is limited to a narrow band around the seed.
Minimum tillage and conservation tillage are interrelated terms that describe tillage practices that leave significant crop residue on the soil surface during pre and post planting tillage operation and/or making the surface porous, cloddy, rough or ridged to enhance precipitation capture and storage. Likewise, the aim of stubble mulch tillage is to keep crop residue (stubble) on the soil surface and standing or partially upright for wind protection and/or snow capture. Stubble mulch is generally specific to the non-cropping (fallow) period.
Q: How do crop rotations impact water conservation in dryland systems?
A: Crop rotations that match precipitation patterns to crop water requirements and critical growth stages during the growing season are generally best suited to dryland systems. These often include crops with shorter growing seasons and crops that are able to predictably produce harvestable grain or forage with less water. In most semi-arid areas, including a fallow period in the rotation is necessary prior to crop with a higher water requirement.
Q: What is fallow and how is it used for water conservation in dryland cropping systems?
A: A fallow period refers to any time period when a field does not have an established crop. The most common purpose for a fallow period in a dryland crop rotation is for water storage in the soil profile for subsequent crops, although breaking pest cycles and matching crops to more favorable growing conditions are also reasons for fallowing. Summer fallow refers to not planting a crop at all during the entire summer growing season. It is typically used in rotation with winter-annual crops such as winter wheat or canola to store up summer precipitation prior to late summer or fall planting. However, even with good weed control and reduced tillage, precipitation storage efficiency is lowest during summer as compared to fallowing during other seasons.
Q: How is plant density (population) used for water conservation in dryland cropping systems?
A: Plant populations are generally kept lower in water-limited dryland systems than irrigated systems for several reasons. First, yield potential is naturally lower in water-limited dryland cropping systems and farmers are best served by plant populations optimized for yield potential. Second, plant transpiration increases as leaf surface area increases up to a maximum of approximately four using a metric called leaf area index. Keeping the plant canopy lower, particularly with row crops, can reduce ET during vegetative growth, saving soil moisture for reproductive growth stages and grain fill later in the growing season.
Q: How can plant arrangement be used for water conservation in dryland cropping systems?
A: For some row crops, planting arrangements can be modified to optimize root interception of soil moisture during critical growing periods. These arrangements include planting techniques referred to as skip-row. This technique skips planting seeds into every other or every third row while increasing the plant count within the row to maintain the same overall number of plants in a given area. In skip-row, the soil moisture in the blank row is not used early in the growing season as the crop root zone is limited to the row, but used later as the root zone expands laterally into these fallow areas. Obviously, good weed control and adequate surface residue is critical to reduce non-beneficial ET to save this moisture for later crop use.