*1.1. Conservation Practices*

This article considers practices that show potential to profitably conserve irrigation water, are accepted in the AAWEP form, and have been adopted by multiple respondents in the 2016 Survey of Mississippi Irrigators. Although many irrigators may decide on adopting several practices simultaneously, this article analyzes adoption practice by practice in order to maximize the number of valid observations for each case.

Soil Moisture Sensors (SMS) are used in irrigation event decision scheduling to prevent yield-limiting water deficit stress on a given crop. SMS gives producers the knowledge of the moisture within the soil profile to make informed and confident irrigation initiation and termination decisions [8] that typically result in increased irrigation efficiency [7,13].

The simplest and most inexpensive (free) upgrade to the baseline irrigation system is Computerized Hole Selection (CHS). Instead of punching uniform holes in layflat poly-tubing, CHS calculates relatively larger holes for parts of the field with long irrigation runs, while shorter parts of the field receive smaller holes to allow water to uniformly reach the end of the field and minimize water runoff [8]. On-farm studies in the Delta area found that CHS achieves water savings of 20 to 25 percent in most situations [14].

"If it can be measured, it can be managed" goes the adage. Pumping flow-meters (meters) are are an important irrigation water management tool compatible with all irrigation systems. Although they do not provide an intrinsic ability to conserve water, they are crucial components, for example, to calculate the optimal size of the holes with CHS [15]. They are also required for cooperator farmers participating in NRCS conservation contracts.

Surge irrigation (surge) allows fields to be divided in two in order to deliver a higher flow rate of water to each half. Water surges down one half of the field until the surge valve flips to deliver water to the other side of the field [8]. The wetting and soaking cycles reduce surface runoff and deep percolation loss while improving water application efficiency by up to 25 percent on the baseline systems with improved infiltration rates documented in sealing silt loam soils [16].

On-Farm Water Storage systems (OFWS) are irrigation water storage structures that are typically designed by NRCS in the Mississippi Delta with the capacity to apply 77 mm of water per hectare per season and meet irrigation requirements for eight out of 10 years [17]. Depending on seasonal conditions, storage capacity, and farmed area, these systems can completely substitute groundwater pumping in some years. NRCS provides technical and financial assistance to producers interested in building OFWS, but many producers face a high opportunity cost to retire productive land to be used for water storage.

The Tailwater Recovery System (TWS) collects irrigation and storm water runoff on the farm in a reservoir (OFWS). TWS increases the amount of water available to irrigation compared to an OFWS filled only by precipitation. This allows OFWS to occupy a smaller surface area and more hectares to be farmed. NRCS estimates that TWS by itself can reduce groundwater pumping by 25 percent.

Micro-irrigation (micro) is a low pressure, low volume, frequent application of water directly to the plant's root zone [18]. It can increase yields and decrease water use by drastically reducing non-beneficial evaporation and virtually eliminating irrigation water runoff. Micro-irrigation is rarely found in the Delta where the soil types and the water quality make the emitters (i.e., nozzles) prone to clogging.

Center pivot-irrigation (pivot) is a type of irrigation that delivers water through sprinklers that create artificial precipitation and are attached to a wheel-driven frame that rotates radially (the arm pivoting on the center). They are highly configurable for a variety of field and crop requirements. Most center pivot systems in the Delta were installed in the 1980s and designed for cotton [19]. However, the original designs are inappropriate to meet the maximum water demands of corn and soybeans. Consequently, there is both adoption of and migration away from center pivot irrigation in the Delta. Similar to micro-irrigation, the soil types and water quality in the Delta present challenges in the form of nozzle clogging and wheels getting stuck in mud.

Pump timers (timer) are a mechanism to program the time or amount of water at which a pump is shut-off. As it helps to automatically or remotely turn the pumps off, it conserves the excess water that might otherwise be pumped, particularly at night [2]. Timers can be employed across irrigation systems for a variety of crops.

Cover crops (cover) are plants that are typically planted during the off season to cover the soil rather than for the purpose of being harvested. They can help sustain and improve soil health [20], microbial populations, and water infiltration, as well as provide benefits in terms of weed control [21]. This is the only conservation practice being analyzed that is not part of AAWEP.
