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1-12 - Lecture 15 Maximizing Linear Move Field Length I The...

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Sprinkle & Trickle Irrigation Lectures Page 179 Merkley & Allen Lecture 15 aximizing Linear Move Field Length M I. The Proc The following procedure for maximizing field length is from Allen, 1983, Univ. Idaho and Allen, 1990 (Irrig. Symp. Paper), and is used in the USUPIVOT comp The basic strategy is to examine differ values to maximize the area covered b minim 1. C x a ). Note that the maximum application depth may be less than MAD*Z*W a with an automatic system to maintain optimal soil water conditions and to keep soil water content high in case of equipment failure (i.e. don’t need to take full advantage of TAW) f' = d x /U d (round down to even part of day) 2. Calculate net and gross application depths: d n = f (U d ) d = d n /E pa 3. Calculate the (presumed) infiltrated depth per irrigation: (D f ) max = d . R e where (D f ) max is the maximum depth to be evaluated, and assuming no runoff 4. For a series of 10 or so infiltration depths, d f , beginning with d f equal to some fraction (say 1/10) of (D f ) max : d f = (i/10)(D f ) max where i = 1 to 10 and, f' = d f DE pa /(100 U d ) f = f' - days off (days off may be zero because the system is automatic), where f' = irrigation frequency for depth d f . DE pa is used here (in percent) because U d is net, not gross edure uter program ent application depths and different w y the sprinkler system, and or to ize labor requirements alculate the maximum application depth per irrigation (d MAD*Z*W
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5. Determine the maximum AR x for a particular d f value using the following two equations (assuming an elliptical pattern): ( )( ) ( ) ( ) 1 n n x n 1 n 1 n 1 SF AR Merkley & Allen Page 180 Sprinkle & Trickle Irrigation Lectures x 2 2 k AR D 1 k n 1 D SS c + + + + f 1.05 1.6 0.5 2 d = π ( 301) where, ( )( ) ( ) − − 0.5 π π 2 2 2 x x x D 1.05AR 1.6AR 0.5 1.6AR + + = + n 1 2 2 2 D 0.5 D (302) in); D is the applied depth (AR) dt (mm); SS is the allowable surface storage (after g) before runoff occurs (usually less than about 5 mm); c is the d f is the total depth 1 x n 1 n 1 f SF AR d n 1 n 1 k k f f 1 2 d 2 d + + SS c and AR x is the peak application per pass (mm/m at time t = pondin instantaneous soil infiltration depth, from SCS soil intake families (mm); k is the coefficient in the Kostiakov-Lewis equation; and of water applied to the ground surface (mm) The parameter “n” is defined as: n = a -1, where “a” is the Kostiakov exponent (see NRCS soil curves at www.wcc.nrcs.usda.gov/nrcssirrig ) Note that SS is a function of the field topography and micro-topography, SF is a relative sealing factor (in terms of soil water infiltration), and may have values in the range of 0 to about 0.36
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