â–¶What is evapotranspiration (ET) and how do I use it to schedule irrigation?
Evapotranspiration (ET) is the total water loss from soil (evaporation) and plants (transpiration); it represents how much water a crop needs per day to replace losses. ET depends on: (1) Climate (temperature, humidity, wind, solar radiation)—hot, dry, windy days have high ET, (2) Crop type (alfalfa uses 2-3x more water than lettuce), (3) Growth stage (young plants use less, mature plants use more). Calculate: ET = reference ET (ET₀, climate-based) × crop coefficient (Kc, crop-specific). Example: on a 85°F, dry day, ET₀ = 0.25 inches/day; for corn in mid-growth (Kc = 1.2), crop ET = 0.25 × 1.2 = 0.30 inches/day water needed. Irrigation scheduling: apply water equal to daily ET to maintain optimal soil moisture. Tools: (1) on-farm weather stations (measure temperature, humidity, wind; estimate ET), (2) online ET calculators (NOAA, extension—input location and crop), (3) soil moisture sensors (measure directly what's available to plants). Irrigation too frequent depletes nutrients and encourages disease; too infrequent stresses yield.
â–¶What are the main irrigation system types and when is each best?
(1) Flood irrigation (furrow, border, basin)—water floods low-lying areas or furrows between rows; cheapest to install, lowest labor, but uses 30-40% more water than modern systems (high evaporation, nonuniform application); best for flat fields of tolerant crops (rice, hay, grain, some vegetables). (2) Sprinkler (impact sprinkler, large-gun, center-pivot, lateral-move)—water sprayed overhead; versatile, uniform application, but some water lost to evaporation and drift (~15-20% loss); best for uneven terrain, vegetables, fruits, turf. (3) Drip (surface or subsurface)—water delivered slowly at soil surface or below; most efficient (80-95% water use), lowest evaporation, precise application, but higher installation cost ($1,000-2,000/acre) and clogging risk if water is poor quality. Subsurface drip (buried lines) is more efficient than surface drip. Choose based on: field topography (flat = flood or pivot, uneven = drip or lateral), crop type (flood for rice, drip for vegetables/berries, sprinkler for forage), water cost (expensive water = drip justified, cheap water = flood acceptable), and maintenance capacity.
â–¶How do I determine soil moisture status and when to irrigate?
Methods: (1) Tensiometer—measures soil water tension (matric potential); range 0-100 cbar where 0 = soil saturated, 100 = very dry. Irrigate when tensiometer reads 30-50 cbar (depends on crop and soil; most crops: irrigate at 30-40 cbar). Cost: $20-50 each, read manually, requires practice. (2) Soil moisture sensor (capacitance or TDR)—measures volumetric water content (%); automated readout, integrates with irrigation controller, can trigger automatic watering. Cost: $100-300 each, multiple sensors per field recommended (every 1-2 acres), automated systems cost $5,000-15,000 installed. (3) Gravimetric sampling—dig soil sample, weigh wet, dry in oven, calculate % water; slow, manual, accurate, used to calibrate sensors. (4) Plant observation—check plant appearance (wilting indicates deficit), measure leaf water potential (expensive equipment, requires training). Strategy: use soil sensors for automation (big fields, expensive water), use tensiometer or plant observation for small fields or hand-watered areas. Monitor weekly; trends guide timing.
â–¶What causes irrigation system failure and how do I troubleshoot?
Common failures: (1) Low pressure—kinked hose, clogged nozzle/emitter, pump cavitation (air in line), leak upstream; diagnose by checking pressure at different points (use pressure gauge), identify lowest point (pressure drop there indicates leak or clog). (2) Non-uniform water distribution—clogged emitters/sprinklers (mineral buildup, debris), pressure variation across field (too-long lines lose pressure), wind drift (sprinklers); clean emitters, install additional pressure regulators at the field, move irrigation time to early morning (less wind). (3) Pump failure—motor doesn't start (electrical problem, blown fuse), runs but no water (dry suction, intake clogged), loses prime (air leak in suction line); check electrical connections, clear intake, reseal suction fittings. (4) Drainage issues—soil waterlogged, disease increases, yield drops; may indicate over-irrigation or subsurface compaction preventing water percolation. Troubleshooting: (1) isolate the problem (pressure, flow, distribution, drainage?), (2) use gauges and sensors, (3) test one sprinkler/drip line at a time. Keep a maintenance log (date, problem, fix, time); patterns reveal chronic issues (mineral buildup in hard water region = filter upgrade needed).
â–¶How do I prevent clogging in drip irrigation systems?
Drip emitters are small (0.5-2 mm holes) and easily clogged by: (1) Sediment—sand, silt, algae; prevent with filters (screen, disc, sand filters; 100-200 micron typical for drip), (2) Mineral deposits (calcium, magnesium, iron)—common in hard water regions; prevent with chlorination (10-15 ppm free chlorine before the drip line) or acid injection (lower pH dissolves minerals), (3) Biological clogging—algae and bacteria grow in warm water; prevent with light-blocking tubing and biocides if severe, (4) Root intrusion—plant roots enter drip tubing through small holes; prevent with herbicide in water (risky, kills some crops) or root barriers. Management: (1) Filter water before entry (essential), (2) Flush lines weekly (close end cap, run water through to clear debris), (3) Monthly or seasonal acid injection if water is hard (acid dissolves mineral buildup), (4) Monthly or seasonal chlorination if biological clogging is observed (frothy water, reduced flow). Prevent is cheaper than curing; one clogged field requires 40+ hours of repair vs. $50-200 in preventive chemicals.
â–¶How do I calculate water needs and plan irrigation season?
Water need = crop ET (inches per day) Ă— number of days from planting to maturity, minus rainfall. Example: tomato needs 18-24 inches total water from transplant to harvest (~100 days). If region gets 8 inches rainfall during that period, irrigation need = 20 - 8 = 12 inches (or 1.2 million gallons per acre, assuming 1 acre-inch = 27,154 gallons). Plan by: (1) estimating season total ET (research or extension estimates), (2) accounting for expected rainfall (average, not dry year), (3) reserving for dry-spell buffer (assume 3-4 week dry spell mid-season), (4) calculating total water volume needed, (5) choosing system and pump size to deliver that volume on schedule. Example: 12-inch need delivered over 100 days = 0.12 inches/day = 1,500 gallons/day on 1 acre. Drip system delivers slowly (~0.1 inch/hour of coverage), so run 1.2 hours/day or 0.5 hours 2Ă—/day. Budget: water cost (often $0.50-2.00/1,000 gallons depending on source and region) = $0.75-3.00/acre/day irrigation season. High-value crops (vegetables, fruits) can justify $500-1,500/acre/season water cost; lower-value crops (hay, grain) cannot.
