Effects of factors influencing spatial and temporal variability of crop yields are usually expressed in crop growth patterns. Consequently, monitoring crop growth can form the basis for managing site‐specific farming (SSF). This experiment was conducted to determine whether crop growth patterns forecast grain yields. Effects of irrigation rates (50 and 80% evapotranspiration, ET), elevation, soil texture, soil NO3‐N, arthropods, and diseases on corn (Zea mays L.) growth and grain yield were evaluated at Halfway, TX, in 1998 and 1999. Data on plant height, leaf area index, leaf dry matter, stem dry matter, and ear dry matter were collected from geo‐referenced locations (DGPS). These data were used to derive total dry matter, crop growth rate, and net assimilation rate (NAR). Grain yields at DGPS locations were classified into four distinct clusters. In 1998, a dry season, clusters were strongly influenced by elevation and soil texture. Grain yields were higher at high elevations where water use was high and soil texture was heavy compared with low elevations. Grain yields at low elevations also were reduced by common smut [Ustilago zeae (Beckm.) Unger] that preferred dry conditions. In 1999, a relatively wet season, clusters included areas with different elevation and soil texture combinations. Measured parameters forecast grain yields better in 1998 than in 1999. Differences in NAR were evident before the 12‐leaf stage, making NAR a potentially useful measurement for early in‐season management decisions. Biomass measurements, for which differences were observed after the 12‐leaf stage, also may be used to formulate decisions for both in‐season and the following season's management.
Episodes of drought stress in upland cotton (Gossypium hirsutum L.) can be detrimental to vegetative growth, yield characteristics, and fiber quality, depending on the specific growth stage drought occurs. Growth, yield, fiber quality, and boll distribution were compared among four cotton cultivars subjected to four growth‐stage specific drought periods that were repeated in three studies over 2 yr in West Texas. Drought timings occurred at pinhead square, early bloom, and two periods of stress during peak bloom. Both years of the study were hot and dry, with minimal rainfall during the episodic drought treatments. Yield was not significantly different among cultivars, nor was there a significant cultivar × irrigation interaction related to cotton yield. However, there were differential effects on fiber quality among cultivars subjected to the different episodic drought timings. Drought stress during squaring resulted in significantly shorter plants with fewer nodes; however, yield was comparable to the highest yields among the other drought stress treatments, and fiber quality parameters were significantly improved compared to all other treatments except full irrigation. The early flowering growth stage was the most sensitive to drought stress and produced the lowest yields, the lowest fruit retention, and poor fiber quality. Drought events at peak bloom resulted in similar yield losses to those at squaring, but poorer fiber quality. This information may be crucial for producers who either have competing demands for water resources or who want to maximize profits or resources after the occurrence of a drought episode.
[1] Although irrigated agriculture is the primary consumer of global groundwater resources, information on recharge rates and sustainable irrigation is limited. The study objective was to fingerprint irrigation return flow to quantify percolation/recharge and to estimate sustainable irrigation levels. This paper focuses on water quantity; a companion paper addresses water quality. Soil samples from 13 boreholes drilled beneath irrigated agroecosystems in the southern High Plains were analyzed for matric potential and waterextractable Cl and NO 3 . Unsaturated zone pore water beneath irrigated agroecosystems can be fingerprinted by higher matric potentials (wetter soils, median mp: −40 m) and higher NO 3 -N (median 71 mg/L) than beneath natural ecosystems (mp −200 m; NO 3 -N 8.1 mg/L) and by higher Cl (720 mg/L) than beneath rain-fed agroecosystems (8.4 mg/L). The range in percolation/recharge rates beneath irrigated agroecosystems is 18-97 mm/a (median 41 mm/a; 5% of irrigation + precipitation) and occurs primarily in response to extreme precipitation events. Similarity in percolation/recharge rates beneath irrigated and rain-fed (4.8-92 mm/a) agroecosystems was unexpected and is attributed to low irrigation applications (median 300 mm/a) and increased crop yield and evapotranspiration in irrigated areas. Regional water table declines are unsustainably large (≥ 30 m over 10,000 km 2 ) in the north and are much lower in the south. Sustainable irrigation in the south would require reduction of the irrigated area from 23% to 9%. Methods developed for quantifying recharge and sustainable irrigation application rates can be applied to groundwater-fed irrigated areas in semiarid regions globally.Citation: Scanlon, B. R., R. C. Reedy, and J. B. Gates (2010), Effects of irrigated agroecosystems: 1. Quantity of soil water and groundwater in the southern High Plains, Texas, Water Resour. Res., 46, W09537,
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