M. Gallardo

Production and water use in lettuces under variable water supply

The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ETc) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m−2 mm−1 and for fresh weight of 48 g m−2 mm−1 . For lettuce irrigated to field capacity, ETc between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ETc was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ETc. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ETc for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.

Water use and production of a greenhouse pepper crop under optimum and limited water supply

Summary Sweet pepper, grown from Autumn to Spring, is a major crop in greenhouse vegetable production systems of the Mediterranean coast in south-eastern Spain. Irrigation water is limited in this region, yet little information is available to assist in irrigation management at the farm and regional levels. The aim of this work was to determine crop evapo-transpiration, water-use efficiency and the effect of continuous water deficits on crop growth and production of pepper grown in plastic greenhouses in two growing seasons. Three irrigation treatments were applied: T1, watered with 100% of the estimated crop water requirement; and T2 and T3 watered with 50% and 20% of the estimated crop water requirements, respectively. Seasonal crop evapo-transpiration (ETc) in treatment T1 was 346–362 mm. The effect of water deficit on crop growth became apparent approximately 80 d after transplanting. The contributions of soil water uptake to total ETc for treatments T2 and T3 were 20–22% and 43–47%, respectively. The response of ETc to water stress was apparent at a threshold value of 55% of available water content (AWC), suggesting an allowable depletion of soil moisture equivalent to 27 mm. For treatments T2 and T3, reductions in total fruit production (relative to treatment T1) were 33% and 62%, respectively; and reductions in marketable fruit production were 47% and 67%, respectively. Water deficit had little effect on total fruit number, but substantially increased the proportion of unmarketable fruits due to their small fruit size, and to high incidences of sunburn and blossom-end rot. Linear relationships were found between both shoot biomass and marketable fresh fruit production with ETc. Mean water use efficiency values for shoot dry matter (WUEb) were 4.5 – 4.7 g m–2 mm–1; for total fresh fruit production (WUEt) between 24 – 33 g m–2 mm–1; and for marketable fresh fruit production (WUEm) between 16.9 – 25.9 g m–2 mm–1. Water stress did not induce early fruit production, or influence the relative distribution of assimilates within the plant.

Response of stem diameter variations to water stress in greenhouse- grown vegetable crops

Summary The ability of indices derived from stem diameter variations (SDV) to detect water stress in vegetable crops grown under greenhouse conditions was evaluated. Two crops, an Autumn-Winter pepper crop and a Spring-Summer melon crop, were grown in soil, in an unheated plastic greenhouse with drip irrigation, in conditions similar to commercial production. A pot study with pepper was also conducted during Autumn-Winter. In each study, two drying cycles were imposed for 7–21 d during the fruit production stage, and un-watered plants were compared with well-watered plants. During each drying cycle, linear variable displacement transducer (LVDT) sensors were used to measure SDV continuously, and daily measurements were made of leaf ( leaf) and stem water potential ( stem). Several indices derived from SDV measurements, including maximum daily shrinkage (MDS) and daily stem diameter growth rate (SGR) were evaluated. In the drying cycles of soil-grown pepper, conducted during Winter, under climatic conditions of low evaporative demand, SDV-derived indices were unaffected by 20-21 d of soil drying, despite both stem and leaf being moderately affected. Pepper plants grown in pots under very similar climatic conditions had appreciable and rapid responses in SDV-derived indices, with MDS increasing and SGR decreasing. In the drying cycles of soil-grown melon, imposed during the relatively higher evaporative demand conditions of Spring and Summer, MDS responded earlier and had larger “signal” values (ratio of values from un-watered to control plants) than leaf or stem. However, there was more variation associated with MDS. In melon, there were strong linear relationships between MDS and both leaf and stem. The present study suggested that SDV-derived indices can be sensitive indicators of plant water status in melon and pepper when grown (a) in pots with a restricted root volume under any climatic conditions, and (b) in soil during periods that do not include climatic conditions of low evaporative demand.

VegSyst, a simulation model of daily crop growth, nitrogen uptake and evapotranspiration for pepper crops for use in an on-farm decision support system

The VegSyst simulation model was developed to assist with N and irrigation management of sweet pepper grown in plastic greenhouses in the Mediterranean Basin. The model was developed for use in an on-farm decision support system with the requirement for readily available input data. Dry matter production (DMP), crop N uptake and crop evapotranspiration (ETc) are simulated on a daily basis. DMP is calculated from daily fraction of intercepted photosynthetically active radiation (PAR), PAR radiation, and radiation-use efficiency. Fraction of intercepted PAR is calculated from relative thermal time. Crop N uptake is calculated as the product of DMP and N content which is described by a power function of DMP. ETc is the product of daily reference evapotranspiration (ETo) using an adapted Penman–Monteith equation, and a daily simulated crop coefficient value. The VegSyst model for soil-grown, greenhouse pepper was calibrated in one crop and validated in three different crops. In the validation, the model accurately simulated crop growth, N uptake and ETc. Relative to measured values, simulated DMP at final harvest was 0.89–1.06, and crop N uptake was 0.97–1.13. Simulated cumulative ETc for complete crops was 0.95–1.05 of measured values.

Assessing crop N status of fertigated vegetable crops using plant and soil monitoring techniques

Abstract Evaluation of crop N status will assist optimal N management of intensive vegetable production. Simple procedures for monitoring crop N status such as petiole sap [NO 3 −–N], leaf N content and soil solution [NO 3 −] were evaluated with indeterminate tomato and muskmelon. Their sensitivity to assess crop N status throughout each crop was evaluated using linear regression analysis against nitrogen nutrition index (NNI) and crop N content. NNI is the ratio between the actual and the critical crop N contents (critical N content is the minimum N content necessary to achieve maximum growth), and is an established indicator of crop N status. Nutrient solutions with four different N concentrations (treatments N1–N4) were applied throughout each crop. Average applied N concentrations were 1, 5, 13 and 22 mmol L−1 in tomato, and 2, 7, 13 and 21 mmol L−1 in muskmelon. Respective rates of N were 23, 147, 421 and 672 kg N ha−1 in tomato, and 28, 124, 245 and 380 kg N ha−1 in muskmelon. For each N treatment in each crop, petiole sap [NO 3 −–N] was relatively constant throughout the crop. During both crops, there were very significant (P < 0.001) linear relationships between both petiole sap [NO 3 −–N] and leaf N content with NNI and with crop N content. In indeterminate tomato, petiole sap [NO 3 −–N] was very strongly linearly related to NNI (R2 = 0.88–0.95, P < 0.001) with very similar slope and intercept values on all dates. Very similar relationships were obtained from published data of processing tomato. A single linear regression (R2 = 0.77, P < 0.001) described the relationship between sap [NO 3 −–N] and NNI for both indeterminate and processing tomato, each grown under very different conditions. A single sap [NO 3 −–N] sufficiency value of 1050 mg N L−1 was subsequently derived for optimal crop N nutrition (at NNI = 1) of tomato grown under different conditions. In muskmelon, petiole sap [NO 3 −–N] was strongly linearly related to NNI (R2 = 0.75 – 0.88, P < 0.001) with very similar slope and intercept values for much of the crop (44–72 DAT, days after transplanting). A single linear relationship between sap [NO 3 −–N] and NNI (R2 = 0.77, P < 0.001) was derived for this period, but sap sufficiency values could not be derived for muskmelon as NNI values were >1. Relationships between petiole sap [NO 3 −–N] with crop N content, and leaf N content with both NNI and crop N content had variable slopes and intercept values during the indeterminate tomato and the muskmelon crops. Soil solution [NO 3 −] in the root zone was not a sensitive indicator of crop N status. Of the three systems examined for monitoring crop/soil N status, petiole sap [NO 3 −–N] is suggested to be the most useful because of its sensitivity to crop N status and because it can be rapidly analysed on the farm.

Tools and Strategies for Sustainable Nitrogen Fertilisation of Vegetable Crops

In intensive vegetable production, N fertiliser applications often contribute to a supply of N that appreciably exceeds crop N requirements resulting in the loss of N to the environment which can result in NO3− contamination of water bodies. There is a range of tools and strategies that can assist vegetable growers to improve N management. These include various methods based on soil analysis or estimation of the soil N supply, N balance calculations, methods based on plant analysis, methods based on monitoring crops with optical sensors, and the use of computerised decision support systems based on simulation models or data bases. Use of these tools has been demonstrated to appreciably reduce fertiliser N application and N losses while maintaining production. The selection of tools to be used by a grower will be influenced by factors such as availability, the grower’s technical level, and economic considerations. For fertigation systems with high frequency N application, a combination of a planning method such as a decision support system with a monitoring method is recommended. Additional tools that can assist in demonstrating to stakeholders the benefit of improved N management are simulation models that provide scenario analysis. Fundamental strategies for improving N fertiliser management are to consider all N sources such as root zone soil mineral N and N mineralised from organic materials, and to partition N application so that it coincides with crop N demand.

Plant–Water Relations

Abstract This chapter deals with the basic principles of plant water relations. Firstly, the role of water in plants is described. The traditional indicators of plant water status are presented together with new methodological approaches that have been recently developed to characterize plant water status. Then, the development of water deficits is considered and how they affect the main physiological processes in plants. Finally, applications of plant water relations to scheduling irrigation will be described and analyzed.

Growth, grain yield and water use efficiency of tritordeum in relation to wheat

Abstract In the search for alternative crops suitable for rainfed mediterranean cropping systems, a new species of cereal × Tritordeum Ascherson et Graebner (Hordeum chilense Roem. et Schultz. × Triticum spp.) has been bred by crossing a wild barley with bread and durum wheats. The productivity and agro nomic characteristics of two experimental lines of tritordeum in relation to wheat were evaluated at Cordoba (south-western Spain) in the 1986/87 and 1987/88 growing seasons. In 1987/88, an early and a later release of tritordeum (recombined and secondary tritordeums) were compared to an early-maturing bread wheat (cv. Cajeme) and a late-maturing durum wheat (cv. Ardente) in terms of tiller and biomass production, harvest index, yield and yield components, evapotranspiration (ET) and water use efficiency (WUE). Only the recombined tritordeum was evaluated against the same early bread wheat and a late bread wheat (cv. Mara) in 1986/87. In 1987/88, both tritordeums and the late wheat had similar phenological development, reaching anthesis about two weeks after the early wheat. Aboveground biomass of secondary tritordeum was similar to both wheats (around 1300 g m-2) while recombined tritordeum produced only 905 g m-2 of biomass. Grain yield of recombined and secondary tritordeums were 23 and 58 per cent of the average yield of both wheats which were similar to each other (5.5 t ha-1). ET was similar for all four genotypes. Consequently, biomass WUE was less in recombined tritordeum than in the other three genotypes (2.3 vs. 3.3 g m-2 mm-1), while WUE in terms of yield was lower in both tritordeums than in the wheats. In both years, tiller production was 30 to 75 per cent higher in the tritordeums than in the wheats. The lower yields of the tritordeums were primarily due to a much larger number of unproductive tillers and to a lower mean grain weight. The large yield improvement in secondary tritordeum relative to recombined tritordeum was due to an increase in biomass and in number of grains per ear. These agronomic characteristics, high grain protein content and the considerable improvement achieved through several generations of breeding suggest that tritordeum may be a valuable alternative winter cereal in mediterranean environments.

Global trends in nitrate leaching research in the 1960–2017 period

Nitrate leaching is the process whereby the nitrate (NO3-) anion moves downwards in the soil profile with soil water. Nitrate leaching is commonly associated with chemical nitrogen (N) fertilizers used in agriculture. Nitrate leaching from different sources and contamination of surface and groundwater is a global phenomenon that has prompted social and political pressure to reduce nitrate leaching and contamination of water bodies. This bibliometric study analyzed global trends in nitrate leaching research. The results showed a rising interest in the last decades in this topic; given the growth tendency over the last years, it was envisaged that the importance on nitrate leaching research will continue increasing in the future. Knowledge on nitrate leaching was mostly disseminated through scientific publications (90% of total documents recovered), both as journal articles and reviews, classified in the Scopus database in the Agricultural, Biological and Environmental Sciences areas. Most publications dealt with soil nitrogen losses from agroecosystems and farmlands and the associated impact on the environment; they were published in journals with a focus on the influence of anthropogenic and soil-crop-animal systems in the environment, and on how such changes in the environment impact agroecosystems. Most documents published on nitrate leaching were indisputably from the United States, followed by China, the United Kingdom and Germany. An analysis of the main keywords showed an overall dominance of the soil nitrogen cycle, fertilizer use in agriculture and water quality aspects. The evolution of main crop species involved in nitrate leaching research showed a rising relevance of research conducted with maize, wheat and grasses from 1990 onwards. The most productive institutions in terms of number of documents dealing with nitrate leaching research, h-index and total citations, were located in the United States, China and the Netherlands. The United States Department of Agriculture stood out, followed by the Chinese Academy of Sciences and Wageningen University and Research. There were clusters of institutions with intercontinental interaction, on nitrate leaching research, between institutions from Europe, Asia and South and North America. Overall, this study has highlighted, from a bibliometric perspective, the rising concern on nitrate leaching. Progress in this field has been made particularly on the impact of the soil-plant-animal system on the environment and agroecosystems, and on fundamental and applied aspects of plant-soil interactions with an emphasis in cropping systems.

Proximal Optical Sensors for Nitrogen Management of Vegetable Crops: A Review

Optimal nitrogen (N) management is essential for profitable vegetable crop production and to minimize N losses to the environment that are a consequence of an excessive N supply. Proximal optical sensors placed in contact with or close to the crop can provide a rapid assessment of a crop N status. Three types of proximal optical sensors (chlorophyll meters, canopy reflectance sensors, and fluorescence-based flavonols meters) for monitoring the crop N status of vegetable crops are reviewed, addressing practical caveats and sampling considerations and evaluating the practical use of these sensors for crop N management. Research over recent decades has shown strong relationships between optical sensor measurements, and different measures of crop N status and of yield of vegetable species. However, the availability of both: (a) Sufficiency values to assess crop N status and (b) algorithms to translate sensor measurements into N fertilizer recommendations are limited for vegetable crops. Optical sensors have potential for N management of vegetable crops. However, research should go beyond merely diagnosing crop N status. Research should now focus on the determination of practical fertilization recommendations. It is envisaged that the increasing environmental and societal pressure on sustainable crop N management will stimulate progress in this area.