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A complete factorial experiment using three nitrogen (67, 156 and 245 lbs N/acre) and three water rates (70, 100 and 130% consumptive use) examined the specific management criteria necessary for obtaining optimum yield and quality of drip- irrigated 'Sweetie '82' sweet corn. The crop was planted on 22 February and harvested on 30 May with an 86/50° F heat unit accumulation of 1444. When present, a nitrogen deficiency greatly decreased marketable yield number of marketable ears/plant mean ear weight, ear length and tip fill. Higher moisture rates generally had less effect on yield and quality than did N rates; however, increasing water rates significantly increased marketable yields and plant height. The effect of N and water rates on N and dry matter accumulation and on diagnostic plant tissue testing results for sweet corn are also presented The maximum marketable yield obtained in this experiment was 7.2 tons per acre, using 245 lbs N/acre and 20.5 inches of irrigation water.

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Osmotic adjustment is one of the adaptive responses of plant species to salinity, In tepary bean seedlings, salinity led to osmotic adjustment in different parts of the seedlings. The osmotic potential of the leaves increased to 340rnM(-1MPa)in seedlings treated with - 0.75 MPa NaCl. Water and osmotic potential of leaves and proximal parr of the roots were more negative than the controls whereas the turgor potential remained about the same. The osmotic adjustment of the tepary bean may result from the synthesis and accumulation of free sugars and amino acids or the accumulation of inorganic ions within the tissue. A quantitative analysis of the sugars and amino acids from salt stress treated tepary bean seedlings showed that they would contribute only -0.15 MPa to the osmotic adjustment whereas inorganic ions would contribute -0.45 MPa. The sum of these osmotic potentials is -0.6 MPa which is -0.4 MPa short of the observed osmotic values. These results suggest that additional substances also contribute to the osmotic adjustment of tepary beans.

A field experiment with subsurface drip irrigated watermelon was conducted on a Casa Grande s.l. soil at the Maricopa Agricultural Center in 1992 to evaluate the field performance of two slow release nitrogen (SRN) fertilizers in comparison to a conventional soluble N source, urea, ammonium- nitrate (UAN-32). Single, preplant applications of 0, 100 and 200 lbs N/acre supplied from methylene urea (Nutralenes) or 100, 150 and 3(X) lbs N/acre from a methylene urea-ammonium sulfate mixture (MUAS) were evaluated in comparison to treatments of UAN-32 containing from 52 to 445 lbs N/acre made in five split applications. Yield response to N rates above 100 lbs/acre were similar for all three N sources, indicating that a single, preplant application of a suitable SRN material at an adequate rate could provide N efficiently over the entire growing season. The highest numerical yield (49.3 tons/acre) was obtained with a N rate of 150 lbs N/acre from the MUAS material. Monitoring of petiole nitrate levels throughout the season indicated that N release from the MUAS was more rapid and more complete than from the methylene-urea product. At suboptimal N rates, i.e. < 150 lbs N/acre, split applications of UAN-32 appeared to be somewhat more efficient than the slow-release products.

Rising water costs and concern for groundwater contamination are driving growers to improve irrigation and fertilization efficiency. A tentative Best Management Practice (BMP) for nitrogen fertilization of watermelon, a high water and nitrogen fertilizer use crop, has been developed, but needs further field verification. Information from tensiometers is used to schedule irrigations and watermelon petiole nitrate levels at critical growth stages are used to recommend rates of nitrogen fertilizer to apply with the objective of producing economic yields while limiting conditions which favor nitrate leaching to groundwater. In 1991, a field experiment consisting of a complete 3x4 factorial arrangement of soil moisture tensions, -12, -7 and -4 kPa, and 60, 214 315 and 500 kg N/ha, respectively, applied through a subsurface trickle irrigation system to watermelon was conducted on a Casa Grande sandy loam at the Maricopa Agricultural Center. Petioles were sampled from the youngest mature leaf beginning at the 3-4 leaf stage and then at major growth stages until first harvest. Harvested melons were weighed and soluble solids, dry matter and N uptake were determined on two representative melons from each experimental unit. An estimate of vine dry matter and N uptake was also determined. Soil samples were taken at 30 cm depth intervals to 1.2 m and analyzed for extractable N. A trench profile method was used to determine root distribution patterns for the three soil moisture treatments receiving optimum N. Petiole nitrate levels were highly responsive to N fertilizer treatments and accurately quantified visual observations of crop N status. Petiole nitrate results also indicated that the preliminary tissue nitrate test was adequate in assisting with a nitrogen management program though minor modifications were necessary. Marketable yield showed a tension x N interaction with a ridge of maximum yield occurring from high soil water tension and low N to low soil water tension and high N with yield reductions on either side of the ridge. Yield estimates along the ridge ranged from 101 Mg/ha (45.4 ton /ac) at -8 kPa tension and 280 kg N/ha to 105 Mg/ha (47.3 ton /ac) at -4.4 kPa tension and 376 kg N/ha. A cost return analysis determined that maximum economic returns were $12,059/ha when 311 kg N/ha were applied in conjunction with -6 kPa soil tension (145 cm water). Unaccounted for N, as determined by an N balance method indicated large amounts of N were unaccounted for when high rates of N were applied under wet soil conditions. N loss was concluded to be due to either leaching and/or denitrification under these conditions.