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The longevity of subsurface drip irrigation (SDI) systems is a key factor in the profitability of these systems when used for lower-value commodity crops (typically the fiber and grain crops). The system management and maintenance protocols, as well as the source water quality, can greatly impact the longevity of these systems. This study evaluated 10 subsurface drip irrigation systems in 2008 and 8 additional systems in 2009 that had been in operation between 6 and 20 years. System uniformity was evaluated by the uniformity parameters, emitter discharge variation, qvar, and the lower quartile distribution uniformity of emitter discharge, DUlq. Pressure measurements along the dripline also were used to determine if qvar was primarily explained by friction losses. Two-thirds of the evaluated SDI systems had qvar less than 20% and DUlq greater than 80 which would be acceptable and one-third of the systems had qvar less than 10% and DUlq greater than 90 which would be good to excellent uniformity. There was very little correlation in system uniformity and system life with the oldest system (20 years) having the greatest uniformity. Uniformity problems on nearly two-thirds of the systems appeared to have been exacerbated by incorrect operating pressure (both too low and too high) with the six best performing systems operating between 65% and 100% of the manufacturer's specified nominal operating pressure. Water hardness and total dissolved salts were the major water quality concerns. Poor maintenance (e.g., no or infrequent chlorination; inadequate filtration system backflushing) appeared to reduce uniformity in between one-third and one-half of the systems. The producer's lack of installation records and operator's guides likely negatively impacted system uniformity through these poor management and maintenance procedures. The use of both qvar and DUlq to evaluate performance of SDI systems appeared to enhance the determination of the primary causes of SDI system nonuniformity.

Some subsurface drip irrigation (SDI) farmers have observed big increases of cotton lint yields just by the addition of small amounts of phosphorus (P). Several questions arise regarding these applications, such as what are the most appropriate rates, whether to split the rates between the phenological stages, and what is the most efficient method to apply P. Nutrients can be either knifed into the soil or injected through the irrigation system. A field experiment was conducted during 2004, 2006, and 2007 to evaluate the effect of knifing versus injecting the phosphorus in the irrigation system, and injecting it in one or two applications. The experimental design was a completely randomized with four treatments consisting of: 1) no P application, 2) knifing the P into the soil, 3) injecting P as phosphoric acid in one application, and 4) injecting P as phosphoric acid split into two applications. In two out of three years higher cotton lint yields were obtained by P application compared to where ...

Subsurface drip irrigation (SDI) has expanded dramatically in cotton producing areas of the southwest United States, especially where furrow irrigation was practiced. There is ancillary evidence that cotton may experience shortages of phosphorus (P) and other nutrients more readily under SDI compared with furrow irrigation. This may be related to the smaller wetted volume of soil and hence smaller root volume under SDI. Some cotton producers using SDI in the Trans Pecos region of Texas have observed large increases in cotton lint yield by the addition of small amounts of P; however, cotton response to different P rates under SDI has not been documented in this region. This article presents results of a field experiment repeated during the 2003, 2004, and 2005 growing seasons where cotton lint yield, quality characteristics, and lint gross return were evaluated for different P application rates. The experiment was completely randomized with four treatments and three replications. Treatments were: 1) no phosphorus applications; 2) injection of 4.6 kg ha-1 y-1 P contained in Miller Solugro® (12-48-8); 3) injection of 32.9 kg ha-1 y-1 P contained in phosphoric acid; 4) injection of 65.7 kg ha-1 y-1 P contained in phosphoric acid. The cost of P treatments ranged from $21.10 to $42.20 ha-1 y-1, but marginal gross returns for lint were $520 to $1,252 ha-1 y-1 more from phosphoric acid and $233 to $872 ha-1 y-1 more from Miller Solugro®. In 2003 and 2004, lint yields and gross returns were greatest for the 65.7-kg ha-1 y-1 P rate, which was similar to recommended rates based on a 2004 soil fertility analysis. In 2005, lint yields and gross returns were greatest for the 32.9-kg ha-1 y-1 P rate, which was slightly below recommended rates based on pre-plant 2005 soil fertility analysis. These results support injecting P at rates based on soil fertility analyses. Both phosphoric acid and Miller Solugro® were suitable for injecting P into SDI systems. The P2O5 application rates increased the productivity per unit of water applied during the three years of the study. Plant petiole analysis in 2004 correlated with P application rates, suggesting a qualitative method to detect P deficiencies during the growing season.

Cotton lint yield, seed mass, fiber quality parameters, gross return, and net return were compared for subsurface drip irrigation (SDI) lateral spacing and installation depth in a clay loam soil in western Texas for three seasons. Drip laterals were spaced either in alternate furrows (2 m) or beneath every planted bed (1 m), and installation depths were either 0.2 or 0.3 m beneath the soil surface. Net return was gross return minus fixed and variable costs. Fixed costs included the annual payment for financing the initial investment of SDI materials and installation (5.00% interest over 10 years), the annual land lease, and the annual depreciation of the SDI system. Variable costs were those associated with cotton production and were similar for the two drip lateral spacings. Lint yield, seed mass, and gross and net returns were significantly greater for the 1 m lateral spacing in the first two seasons, but these parameters were significantly greater for the 2 m lateral spacing in the third season. These parameters were consistently greater (either numerically or significantly) for the 0.3 m lateral depth in all seasons. Most fiber quality parameters were not significantly different, and no consistent trends were observed. Lint yields ranged from 640 to 1,635 kg ha-1, and net returns ranged from -$395 to $1,005 ha-1. The low lint yield and resulting net loss were due to a germination failure in the second season for the alternate furrow spaced laterals. Additional seasons of study are required before conclusions might be drawn concerning the most economic lateral spacing for cotton production in the Trans-Pecos region of Texas, but the 0.3 m lateral depth resulted in greater net returns than the 0.2 m lateral depth.

Cotton production is an important economic base for western Texas; however, the region has erratic and limited rainfall and is dependent on limited groundwater supplies. Maximizing water use efficiency (WUE) for cotton lint yield is therefore a strategic goal in conserving limited water resources. In this study, different row spacings, planting patterns, and irrigation levels were evaluated to investigate water use efficiency for cotton under subsurface drip irrigation (SDI). An experiment with three row spacings, three planting patterns, and four water levels was conducted during three years in western Texas. The row spacing treatments were ultra–narrow (UNR), 0.76 m, and 1.02 m. The planting patterns for the 0.76–m and 1.02–m row spacings were every row planted, one planted and one skipped, and two planted and one skipped. The UNR cotton was solid–planted in 0.25–m rows in 1997 and in 0.38–m rows in 1998 and 1999. Driplines were placed beneath each planted row, except in the case of the UNR rows where the rows were planted over the 0.76–m dripline spacing. The UNR and the 0.76–m row spacings resulted in higher WUE than the 1.02–m row spacing for the highest water level in 1997, and for the lowest water level in 1998 for the every–row pattern. When the three years of data were combined for analysis, it was observed that for the lowest water treatment (0.6 mm/d in–season irrigation), the UNR spacing produced a higher WUE (0.258 kg/m3) than the 0.76–m and 1.02–m row spacings (0.198 kg/m3). The average WUE of the UNR spacing for three years of the experiment was 11.7% and 21.3% higher than the 0.76–m and 1.02–m row spacings, respectively. Although the 0.76–m and 1.02–m row spacings were not significantly different, the WUE of the 0.76–m row spacing was 10.5% higher than that of the 1.02–m row spacing. Therefore, we conclude that, under our conditions, row spacing can have a moderate impact on WUE for SDI systems. The narrower cotton spacing exhibited trends toward higher WUE. When the planting patterns were analyzed by combining three years of data, it was found that planting pattern did not have an influence on WUE for the 0.76–m and 1.02–m row spacings.

A successful maintenance program may increase the longevity of Subsurface Drip Irrigation (SDI) systems. This study evaluated ten subsurface drip irrigation systems that have longevities between eight and twenty years. The system performance parameters: Christiansen’s Uniformity Coefficient (CUC) and Low Quartile Distribution Uniformity (DUlq) was assessed for ten SDI systems and their maintenance practices were documented. The longevity of the system may be related to the water quality of the aquifer. The aquifer does not present any major problem related to chemical compounds that can enhance clogging problems. The uniformity of the ten systems evaluated was greater than 79.3%. Maintenance practices among farmers were very similar. Most of the farmers flush their filters daily for at least 1.33 minutes and flush the manifolds once a year. Farmers inject sulfuric acid once a year lowering the pH to less than 3.5. Others use N-Phuric instead of the sulfuric acid. The sulfuric acid that most farmers use is 95% and they apply it at approximately 0.97 L h-1 (1 gal/10 acres). Some farmers inject chlorine every year, but others just every 7 years. The chlorine is Univar's sodium hypochlorite, which is 12% and they apply it at approximately 0.47 L h-1 (1 gal/20 acres). A good maintenance program and the use of good quality water may increase the longevity of the system.

Cotton lint yield and quality were investigated for different irrigation frequencies using subsurface drip irrigation (SDI) under limited water conditions (1.7 mm day–1) in the St. Lawrence region of West Texas. Two frequency intervals were studied during two years; these intervals were 4 and 16 days in 1999 and 2 and 8 days in 2000. Each treatment was replicated four times, and the total amount of water applied each year was the same. The soil was a silty clay loam soil underlain by caliche just below 90 cm from the surface. In both years, there were no significant differences between frequency treatments in lint yield, micronaire, fiber length, fiber strength, uniformity, or gross returns. Using the loan values as an indicator of lint quality, cotton loan values were highly significant in 1999, but were not different in 2000. With no major advantage in increasing irrigation frequency using SDI under deficit conditions, these results may have an impact on the agronomic practices of the region where water is very limited. Low frequency irrigation may allow farmers to have more flexibility in managing their irrigation systems and avoid the additional expense of automating a microirrigation system.