Cotton yield and applied water relationships under drip irrigation

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Abstract

Different irrigation scheduling methods and amounts of water ranging from deficit to excessive amounts were used in cotton (Gossypium hirsutum L.) irrigation studies from 1988 to 1999, at Lubbock, TX. Irrigation scheduling treatments based on canopy temperature (Tc) were emphasized in each year. Surface drip irrigation and recommended production practices for the area were used. The objective was to use the 12-year database to estimate the effect of irrigation and growing season temperature on cotton yield. Yields in the irrigation studies were then compared with those for the northwest Texas production region. An irrigation input of 58 cm or total water application of 74 cm was estimated to produce maximum lint yield. Sources of the total water supply for the maximum yielding treatments for each year averaged 74% from irrigation and 26% from rain. Lint yield response to irrigation up to the point of maximum yield was approximated as 11.4 kg ha−1 cm−1 of irrigation between the limits of 5 and 54 cm with lint yields ranging from 855 to 1630 kg ha−1. The intra-year maximum lint yield treatments were not limited by water input, and their inter-year range of 300 kg ha−1 was not correlated with the quantity of irrigation. The maximum lint yields were linearly related to monthly and seasonal heat units (HU) with significant regressions for July (P=0.15), August (P=0.07), and from May to September (P=0.01). The fluctuation of maximum yearly lint yields and the response to HU in the irrigation studies were similar to the average yields in the surrounding production region. The rate of lint yield increase with HU was slightly higher in the irrigation studies than in the surrounding production area and was attributed to minimal water stress. Managing irrigation based on real-time measurements of Tc produced maximum cotton yields without applying excessive irrigation.

Introduction

Viewed from the perspective of water stress, the purpose of irrigation is to keep crop water status at a level that maximizes yield within the constraints of irrigation supply and growing season weather. Irrigation provides varying percentages of total crop water supply depending on the climate and irrigation capacity. Among US cotton growing regions, irrigation ranges from being supplemental to rain to being the primary source of water for production.

The cotton production region within a 130-km radius around Lubbock, TX is semi-arid where about one-half of the cotton acreage is non-irrigated and yields vary with rainfall. The average lint yield of irrigated and dryland cotton production in the 25-county area around Lubbock was 571 and 332 kg ha−1, respectively, from 1977 to 1998.

Numerous cotton irrigation studies have focused on irrigation scheduling to optimize yield and water use efficiency. Over a 3-year period, cotton yield responded to frequency of irrigation using the low energy precision application (LEPA) system for applying irrigation (Bordovsky et al., 1992). For irrigation intervals ranging from 3 to 15 days, the optimum interval for yield was 3 days for water application rates varying from deficit to full soil water use replacement. Radin et al. (1989) reported that cotton yield increased as the interval between water application decreased even if the amount of water was unchanged in the arid climate of Arizona. They concluded that high frequency drip irrigation (1–2-day intervals) prevented cyclic water stress and deterioration of the root system compared to low frequency (2-week intervals). Low and high frequency cotton irrigation resulting from irrigation applications as determined by allowable soil water depletions of 55 and 30%, respectively, was compared in level basins by Hunsaker et al. (1998) where the total water application was equal in both frequencies. Lint yields for high frequency irrigation were 15 and 20% higher than for low frequency irrigation in the first and second years of the study. The question of whether the benefits of high frequency irrigation with a drip system could be achieved using a less expensive delivery system to apply extra irrigations during peak fruiting of cotton was addressed by Radin et al. (1992). One supplemental flood irrigation in level basins increased seed cotton yield 15% over a 10- or 14-day interval control, two supplemental irrigations increased yield 25%, and daily drip irrigation increased yield 40%. Doubling the number of irrigations for a short period during peak fruiting achieved much of the benefit of daily drip irrigation.

Since 1988, we have used different criteria to schedule drip irrigation of cotton. Canopy temperature (Tc) was a common criterion used in some irrigation scheduling treatments that were evaluated each year. The combined information from these studies resulted in a dataset that includes different irrigation quantities and lint yields produced under weather regimes spanning a 12-year period. Using this database, the objectives of this report are to (1) estimate the yield response of cotton to varying amounts of drip irrigation, (2) estimate the relationship between growing season temperature and cotton yield, and (3) compare the cotton yield response in the irrigation studies with the yield trends for the northwest Texas production region.

Section snippets

Procedure

Cotton irrigation scheduling was studied from 1988 to 1999 using Tc to define irrigation signals for scheduling. The goal of these studies was to develop an automated method requiring only a few measurements to accomplish irrigation scheduling. Continuous Tc measurements and computation of 15 min averages was common across all years. The time interval for making irrigation decisions was 15 min from 1988 to 1994 when an average canopy temperature of at least 28 °C was an irrigation signal.

Results

Field studies were usually planted during the middle of May, DOY 130–DOY 140, which is normally the optimum time for cotton (Table 1). The exceptions were 1992 which was replanted because cool temperatures and rain damaged seedling stands, and 1996 which had four planting dates between DOY 116 and DOY 154. HU are a method of quantifying seasonal heat input from air temperatures and included the period from planting date through September. Irrigation normally began at first square and continued

Discussion

The irrigation studies were conducted with drip irrigation which uniformly applied water and was precisely metered. Testing during 1988–1990 included different temperature thresholds which scheduled irrigation in 15 min intervals and were compared with weekly irrigation intervals that replaced depleted soil moisture. Automated irrigation based on canopy temperature produced cotton yields that were generally higher than the soil water replacement method. The 1991 and 1992 tests used different

Conclusions

The results from these studies contain several significant items which should be emphasized because of their importance to cotton production management. Maximum yields were estimated to occur for total irrigation amounts near 58 cm or total water application of 74 cm between planting and crop maturity. The average yield of 1500 kg lint ha−1 for the maximum yield treatments could not have be achieved without an irrigation system that allowed timely and uniform water application. At the point of

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