Agriculture consumes more than two thirds of the total freshwater of the planet. This issue causes substantial conflict in freshwater allocation between agriculture and other economic sectors. Regulated deficit irrigation (RDI) is key technology because it helps to improve water use efficiency. Nonetheless, there is a lack of understanding of the mechanisms with which plants respond to RDI. In particular, little is known about how RDI might increase crop production while reducing the amount of irrigation water in real-world agriculture. In this review, we found that RDI is largely implemented through three approaches: (1) growth stage-based deficit irrigation, (2) partial root-zone irrigation, and (3) subsurface dripper irrigation. Among these, partial root-zone irrigation is the most popular and effective because many field crops and some woody crops can save irrigation water up to 20 to 30 % without or with a minimal impact on crop yield. Improved water use efficiency with RDI is mainly due to the following: (1) enhanced guard cell signal transduction network that decreases transpiration water loss, (2) optimized stomatal control that improves the photosynthesis to transpiration ratio, and (3) decreased evaporative surface areas with partial root-zone irrigation that reduces soil evaporation. The mechanisms involved in the plant response to RDI-induced water stress include the morphological traits, e.g., increased root to shoot ratio and improved nutrient uptake and recovery; physiological traits, e.g., stomatal closure, decreased leaf respiration, and maintained photosynthesis; and biochemical traits, e.g., increased signaling molecules and enhanced antioxidation enzymatic activity.

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On agricultural lands, animal waste disposal as fertilizer has been practiced since the beginning of agriculture. However, the practice has been an environmental concern in recent years due to over disposal of animal waste in some instances. This study evaluated soil NO3 response to beef‐manure application on a corn (Zea mays L.) field and tested the Root Zone Water Quality Model (RZWQM) for manure management. The experiment site was located in Northeastern Colorado on a silage‐corn field with a history of fertilization with beef manure every fall after corn harvest. To study the residual effect of long‐term manure application, 582 kg ha‐1 of manure‐N was applied to the east side of the field in the Fall of 1993, 1994, and 1995, while the west side received manure in 1993 only. Average silage‐corn yields from the west site were 25.4, 31.9, and 22.5 Mg ha‐1 for 1994, 1995, and 1996, respectively, which were not significantly different from that harvested from the east site (25.1, 30.9, and 24.3 Mg ha‐1, respectively). Average soil NO3 concentrations decreased significantly from 14.9 to 8.5 mg N kg‐1 in the top 30 cm of soil, and from 5.4 to 3.7 mg N kg‐1 in the 30‐ to 60‐cm soil profile after stopping manure application. No significant difference in soil NO3 concentrations between the manured and not‐manured sites was found below 60 cm. Average plant N uptake ranged from 140 to 362 kg N ha‐1 and was not significantly different between the two sites. The RZWQM was calibrated on the basis of the measured silage‐corn yield and plant N uptake, and was then used to predict soil NO3 concentration and total water storage in the soil profile. Generally, the calibrated model provided adequate predictions for both NO3 and soil water content with r2 > 0.83. The model was further used to evaluate alternative scenarios of manure and water management.

Nonsenescence and sweet culms are being incorporated into cultivars of grain sorghum [Sorghum blcolor (L.) Moench.] for potential improvement in yield. Clarification of carbohydrate production and accumulation patterns within the culm during grain filling is needed for guidance in breeding. Data on culm carbohydrate levels are also needed to evaluate blomass for possible energy uses. A senescent, hybrid, cultivar designated 37 and three non senescent, hybrid, cultlvars designated PS, 65, and 6R were harvested at three stages of maturity: (i) 15 days post anthesls (PA), (il) black layer (BL), and 15 days post black layer (PBL). Panicles on some plants within each replicate were also removed at BL Glucose, fructose, sucrose, and starch concentrations were determined on the culms. Culm and total plant weight, kernel weight, and grain per panicle were also measured. Culm glucose levels at PA were 90.5, 48.1, 39.5, and 12.6 mg/g oven dry weight (ODW), respectively, for PS, 6R, 65, and 37. Glucose levels declined at each successive harvest except in cultivar 65. A similar pattern was obtained for fructose at PA with values of 78.8, 44.2, 43.7, and 21.1 mg/g ODW for the same cultivar sequence. Levels of sucrose decreased from PA to BL by 66.8 and 21.9 mg/g ODW, respectively, for P5 and 65, and then increased to 124.6 and 173.3 mg/g. Sucrose increased in 6R at each maturity stage and a significant increase to 303 mg/g ODW was obtained in PBL. Slight increases of sucrose occurred in 37 during the successive maturing stages. Starch levels increased at all stages in 6R, but declined from PA to BL in PS, 65, and 37, then increased by PBL. Weight/100 kernels was 2.86, 2.80, 2.17, and 1.91g at PBL, and grain weight/panicle was 66.7, 66.5, 55.3, and 48.2g, respectively for PS, 65, 6R, and 37. These results suggest that sweet culms do not reduce grain weights. Culm sugar accumulation patterns differed among cultivars. Patterns exhibited by P5 and 65 appeared to be desirable for grain production and possibly as biomass for energy use since the culms continued to fill with sugar after BL. The nonsenescing cultlvars contained significantly more carbohydrates at all maturity stages than the senescing one. Plants with panicles removed at BL had accumulated more culm carbohydrates at PBL than reported above in most cases.