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- Author or Editor: M. B. Kirkham x
Horticultural crops use a large amount of good quality water. For example, in the dry west of the United States, nearly one-half of the domestic water supply is applied to lawns and ornamental plants (42, 61). In order not to waste water, it should be applied only when the plants are under drought stress. To determine when supplemental irrigation is required, plant water status needs to be measured. The objective of this paper is to outline instruments now being used to measure the water status of plants. In particular, instruments that monitor water potential, osmotic potential, turgor potential, stomatal resistance (reciprocal of stomatal conductance), and canopy temperature are discussed. The advantages and disadvantages of these measurements are described. Previous reviews on instruments for plant-water studies include those by Barrs (2), Monteith (96), Slavik (136), Turner (159), Squire, Black, and Gregory (139), and Hanan (50). Plant-water measurements made on some specific horticultural crops have been detailed. These crops and the references are as follows: citrus (Fortunella, Poncirus, Citrus) (74), apple (Malus) (79), peach (Prunus) (26), grape (Vitis) (137), and small fruits [strawberry (Fragaria, blueberry (Vaccinium), raspberry (Rubus), cranberry (Vaccinium), gooseberry (Ribes), and currant (Ribes)] (35).
If wastewater is to be recycled safely for agricultural production the problems associated with using it on vegetables need to be known. The objective of this review is to determine those problems. Several earlier reviews dealing with the use of wastewater in agriculture have been published (5, 7, 9, 19, 27, 30, 31, 42). Raw wastewater, or primary effluent, is not considered in this paper because secondary effluent is the type of wastewater generally used for irrigation in the United States (42). Primary treatment involves only settling tanks, from which anything in the raw sewage that can float or sink is removed. Sewage from primary treatment is subjected in secondary treatment to the action of living microorganisms: e.g., activated-sludge processes, trickling filters, treatment ponds (42). Also, this paper is limited in discussion to municipal waste-water and does not mention wastewater from industry, including wastewater from vegetable-processing plants. This review is divided into 3 areas: physical, chemical, and biological problems.
Chrysanthemum plants (Chrysanthemum morifolium Ramat. cv. Bright Golden Anne) were grown for 84 days in plastic pots containing media treated with inorganic fertilizers or liquid sewage sludge, added at a rate of 50, 100, or 200 ml/week, to determine if sludge could be used as a fertilizer. Plants grown with sludge at all application rates had higher N and lower K concentrations compared to plants grown with inorganic fertilizers. Leaf concentration of P, Ca, Mg, Fe, Zn, Cu, Cd, Ni, and Pb of plants grown with 50 ml sludge/week were similar to plants receiving inorganic fertilizers. As sludge application rate increased, leaf concentrations of Fe and Cu increased of plants grown in media consisting of all sand or all peat and Zn increased in leaves of plants grown in the standard greenhouse media (1 soil: 1 sand:l peat, by volume). Sludge-treated media had a higher pH and extractable Cu concentration, and a lower extractable K concentration, than media without sludge. Plants receiving 50 ml sludge/week grew as well as plants grown with inorganic fertilizers.
In 1992, all governmental resourcing and investment in New Zealand, including that for science, underwent dramatic reform. The global philosophy driving the reform was new public management—a method by which nations could be run more economically by emulating the commercial world. Central to the reform was separation of policy, purchasing (investment), and providers (in the case of research scientists). The reform led to a large reduction in the number of governmental scientists. For example, in 1 year alone, 2001–2002, the Horticultural and Food Research Institute, one of the nine governmental branches of science, lost 51 staff members, 10% of its work force. Over a decade later after the establishment of the reform, in July 2003, the New Zealand government's investment agency announced its budget for the next 6 years. The government-funded science sectors considered to do modern research such as computer technology and biotechnology, and halved funding for land-related sciences. The reduced budget dramatically limited New Zealand's capacity for research in soil and land-use science and ended all research positions in this area (38 jobs). Public outcry through newspaper editorials and from leading businessmen, along with effective leadership from the scientific community, led to the reestablishment of funding in the form of a virtual national center called Sustainable Land Use Research Initiative (SLURI). The elimination of funding for soil and land-use science research in New Zealand was an unexpected and potentially disastrous result of new public management. New Zealand's experience has relevance for the United States, because budgets for agricultural research are being severely reduced or converted to competitive funding. The U.S. President's fiscal year 2006 budget proposed to cut formula funding by 50% and to zero it out in fiscal year 2007. The funds would have been put in competitive grants. In New Zealand, the lack of ability to respond to a scientific problem demonstrated that a balance must be maintained in funding decisions so that scientific capability is retained to solve unforeseen future problems.
Chrysanthemum plants (Chrysanthemum morifolium Ramat. cv. Bright Golden Anne) were grown for 84 days in plastic pots containing 6 different media treated with inorganic fertilizers or liquid digested sewage sludge at 50, 100, and 200 ml/week. Plants grown in 1 soil: 1 sand: 1 peat, 1 soil: 1 sand, and 1 soil: 1 peat were similar to each other in size, and larger than plants grown in 1 sand:1 peat, all sand, or all peat. Peat-grown plants were smallest. Plant size and flower diameter decreased with increasing rates of sludge application. Plants fertilized with inorganic sources of fertilizer looked the same as those grown with 50 ml/week sludge (6 mm), except the sludge-treated plants were shorter and had a smaller dry weight. Plants treated with 50 ml/week sludge had flowers with a diameter and dry weight equal to those of flowers grown with liquid or pelletized inorganic fertilizer.
Water and turgor potentials of callus tissue from the cactus Echinopsis turbinata L. increased with increasing concentration of kinetin. Osmotic potential showed no consistent trend with an increase in concentration of kinetin or p-chlorophenoxyacetic acid (p-CPA).
A survey was conducted of 81 growers managing 185 high tunnels in Missouri, Kansas, Nebraska, and Iowa to collect information about their high tunnel management practices. The survey was administered from 2005 to 2007 using internet-based and written forms. The average respondent had 4 years of high tunnel experience. The oldest tunnel still in use was 15 years old. Twenty-five percent of respondents grew crops in their high tunnels year-round. Tomato (Solanum lycopersicum), lettuce (Lactuca sativa), spinach (Spinacia oleracea), cucumber (Cucumis sativus), pepper (Capsicum spp.), leafy greens, and flowers were the most common crops. Organic soil amendments were used exclusively by 35% of growers, and in combination with conventional fertilizers by an additional 50% of growers. The summary of management practices is of interest to growers and the industries and university research and extension scientists who serve them. Growers typically reported satisfaction with their high tunnels. Growers with more than one high tunnel had often added tunnels following the success of crop production in an initial tunnel. Labor for crop maintenance was the main limiting factor reported by growers as preventing expanded high tunnel production.
Two species of tomato, Lycopersicon chilense Dun. and Solanum pennellii Corr., which have drought-resistant characteristics, were compared to the commercial tomato, Lycopersicon esculentum Mill. cv. Campbell 1327, to evaluate the effects of water deficits on germination and early seedling growth at 25, 30, and 35°C. Five levels or water stress (0, −2, −4, −6, and −8 bars) were maintained by solutions of polyethylene glycol (PEG) 6000. Germination of dry seed was inhibited more by water stress than by growth of the germinated seedlings of each species. Germinated seed of all species were able to continue growth at 35° plus water stress at all levels, while germination under the same conditions was totally suppressed. The water-sensitive phase of germination occurred just prior to radicle emergence. Emergence was not affected by sowing germinated seed in a drying soil; but sowing dry seed under the same conditions resulted in a decrease in emergence. Germination and seedling growth of L. chilense and S. pennellii were more sensitive to water stress than L. esculentum at 25°. At 30 and 35°, L chilense, S. pennellii and L. esculentum had similar rates of germination and similar amounts of early seedling growth.
The effects of water deficits were examined on osmotic regulation of germinating seedlings of tomato (Lycopersicon esculentum Mill cv. Campbell 1327). Seed were germinated in aerated water and then grown for an additional 2 days in Petri dishes. The germinated seeds were then transferred to water potentials of 0 to −6 bars in 2-bar increments. Mannitol and water was used to obtain the desired water potential of the media. Water relations, growth rates and reducing sugars, non-reducing sugars, amino acids, proline, nitrates, phosphates, potassium, and electrical conductivity were determined for roots and shoots at different water stresses. As water stress increased, osmotic adjustment occurred in the roots which accounted for the maintenance of turgor and growth. During the same period, little adjustment occurred in the shoots and consequently growth decreased. Turgor potential was highly correlated with growth rates for both plant parts. All solutes measured, except proline, generally increased in the roots and decreased in the shoots as water stress increased. Proline increased in both plant parts during the same period. Thus, solute regulation occurred during water deficits. Osmotic regulation in germinating tomato seedlings appears to be an adaptive feature during periods of water stress.
Growers have indicated that changes in soil quality under production in high tunnels is an important problem, but these have not yet been quantified or critically assessed in the central Great Plains of the United States. We conducted surveys of grower perceptions of soil quality in their tunnels (n = 81) and compared selected soil quality indicators (salinity and particulate organic matter carbon) under high tunnels of varying ages with those of adjacent fields at sites in Kansas, Missouri, Nebraska, and Iowa in the United States. Fourteen percent of growers surveyed considered soil quality to be a problem in their high tunnels, and there were significant correlations between grower perceptions of soil quality problems and reported observations of clod formation and surface crusting and to a lesser extent surface mineral deposition. Grower perception of soil quality and grower observation of soil characteristics were not related to high tunnel age. Soil surface salinity was elevated in some high tunnels compared with adjacent fields but was not related to time under the high tunnel. In the soil upper 5 cm, salinity in fields did not exceed 2 dS·m−1 and was less than 2 dS·m−1 under 74% of high tunnels and less than 4 dS·m−1 in 97% of high tunnels. The particulate organic matter carbon fraction was higher in high tunnels than adjacent fields at 73% of locations sampled. Particulate organic matter carbon measured 0.11 to 0.67 g particulate organic matter per g of the total carbon under high tunnels sampled. Particulate organic matter carbon in the soil was also not correlated to age of high tunnel. Soil quality as measured in this study was not negatively impacted by use of high tunnel structures over time.