Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2010
Publication Date: 4/19/2010
Citation: O'Shaughnessy, S.A., Evett, S.R. 2010. Canopy temperature based system effectively schedules and controls center pivot irrigation of cotton. Agricultural Water Management. 97(9):1310-1316. Interpretive Summary: Irrigation scheduling is the process of deciding when to irrigate and how much to apply so that crop quality, yield, and water use efficiency are optimized. As water becomes more scarce in the United States, optimizing water use efficiency (the amount of crop yield gained per unit of water applied) is key to supporting farm income and viability. In this two year study, scientists at the USDA-ARS Conservation & Production Research Laboratory, Bushland, Texas, investigated the use of automatic irrigation scheduling (timing irrigations without human intervention) for cotton production in the Texas High Plains Region. The method of scheduling used depended on crop leaf temperature, which was measured automatically with equipment designed by the scientists. Results were compared with those from irrigation scheduled by measuring soil water content. Four irrigation amounts were also studied, ranging from full, through moderate and severe deficit, to no irrigation (dryland). The results showed that lint yield was not different between the two irrigation scheduling methods in one year, but was larger for the automatic method in the second year for full and moderate deficit irrigation levels. For both years, the irrigation water use efficiency was significantly greater for the automatic irrigation method within each treatment, which indicates that the method and equipment developed can improve sustainability and profitability of cotton farming.
Technical Abstract: Cotton is a perennial plant with an indeterminate growth pattern that is typically produced like an annual, but requires proper management to effectively produce high yields and quality in a thermally limited environment like the northern Texas High Plains. In 2007 and 2008, we investigated the effect of irrigation scheduling/control method and amount on cotton (Gossypium hirsutum L.) yield and water use efficiency. Methods were automatic irrigation scheduling and control of a center pivot system, and manual irrigation to replenish soil water to field capacity. Cotton was irrigated with LEPA (low energy, precision application) drag socks in furrow dikes; three blocks were irrigated manually and three were irrigated automatically. Six replicates of the manual and automatic irrigation treatments were included in the randomized block design. Manual irrigations were based on the weekly replenishment of soil water to field capacity in the top 1.5 m of the soil profile and included a fully irrigated treatment (I100), and treatments receiving 67% (I67) and 33% (I33) of the I100 amount, plus a non-irrigated treatment (I0). Automatic irrigations were triggered using a time temperature threshold (TTT) algorithm, which was designated as the I100 treatment, and treatments receiving 67% and 33% and 0% of that amount (I67, I33 and I0, respectively). In 2007, overall mean lint yields (102.3 and 101.6 g m**-2, manual and automatic, respectively) were not significantly different. Similarly, yields were not significantly different across automatic and manual treatments in the same treatment level, with the exception of the I67 treatment where the manual treatment yields were 11% greater. In 2008, the mean yields were 70% less than those in 2007 for both methods of irrigation (30.3 and 30.9 g m**-2, manual and automatic, respectively) due to harsh climatic conditions at emergence and heavy rainfall and cooler temperatures in the month of August. Yields from the automatically irrigated plots in the I100 and I67 treatments, however, were significantly greater than yields from the corresponding manually irrigated plots; though there was no significant difference between yields in the drier treatments (I33 and I0) plots. These results indicate that the TTT algorithm is a promising method for auto-irrigation scheduling of short season cotton in an arid region. However, further studies are essential to demonstrate consistent positive outcomes.