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Durum grain quality is affected by many factors, but water and nitrogen are factors that the grower can control. The purpose of this research was to determine 1) the nitrogen application rate required at pollen shed to maintain adequate grain protein levels if irrigation is excessive or deficient during grain fill and 2) if nitrogen applications during grain fill can elevate grain protein. Field research was conducted at the Maricopa Agricultural Center using the durum varieties Duraking, Minos, and Turbo. The field was treated uniformly until pollen shed when nitrogen was applied at rates of 0, 30, and 60 lbs /acre. During grain fill, the plots were irrigated based on 30, 50, or 70% moisture depletion. In a separate experiment, nitrogen fertilizer was applied at a rate of 30 lbs N /acre at pollen shed only, pollen shed and the first irrigation after pollen shed, and pollen shed and the first and second irrigation after pollen shed. Increased irrigation frequency during grain fill decreased HVAC from 93 to 81%. Increasing nitrogen rate at pollen shed from 0 to 30 and 30 to 60 lbs N /acre increased protein from 11.6 to 12.5% and 12.5 to 13.3% and increased HVAC from 79 to 89% and 89 to 94 %. Nitrogen fertilizer application at the first irrigation after pollen shed increased grain protein content from 12.9 to 13.6% and application at the first and second irrigation after pollen shed increased grain protein content further to 14.1% averaged over varieties. Nitrogen fertilizer application during grain fill may not be too late to increase grain protein content.

Research conducted recently suggested that application of nitrogen fertilizer from flowering until the dough stage could increase grain protein concentration in durum even if nitrogen applications earlier in the season were adequate for optimum yield. We tested the ability of late season nitrogen application to increase protein at commercial farms in Buckeye, Casa Grande, and Vicksburg. Late season nitrogen increased protein by nearly two percentage points in two out of the three locations. No response was measured at the third location possibly due to high rates or nitrogen earlier in the season. The cost of the late season fertilizer at 35 to 50 lbs N /acre was about $15 /acre. The fertilizer was paid for at the two location where a response was obtained by 1) the slight yield increase of 310 lbs /acre which was worth about $23 /acre and 2) the difference in dockage or premiums paid for protein which was worth about $38 /acre. It is possible that lower stem nitrate levels could be used to determine whether or late applications of nitrogen will increase protein, but we currently do not have a method to determine if protein will be over the critical level of 13% or if HVAC will be over the critical level of 90 %.

Nitrate content of the lower stem tissue of small grains is used as a guideline for nitrogen fertilization. The turnaround time for nitrate analysis in a commercial lab is usually 1 to 3 days. Nitrate quick tests have been suggested as a means of obtaining results on a more timely basis. The quick tests analyze nitrate in the sap or juice squeezed out of the tissue. A nitrate test conducted by a commercial lab is performed on the dried and ground tissue. In this study, I found that the quick tests on plant sap are not as accurate as conventional tests on dried tissue since the moisture content of the fresh plant tissue varies depending on its nitrate content and the growth stage of the plant. We compared the following quick test methods: nitrate test strips, a colorimetric procedure, and a hand held nitrate electrode. Nitrate test strips were not sensitive enough to be useful and were difficult to compare to the color charts. An electronic strip reader could alleviate this difficulty and make the strips a viable option. Colorimetric procedures, or those that rely on nitrate producing a colored solution with certain chemicals added, are not adapted to analyzing plant sap since the green color and organics in the sap interfer with the color produced by the nitrate. The hand held nitrate electrode, or Cardi meter, was the simplest and most accurate method we experimented tested. Quick tests for nitrate in the sap have the following disadvantages: 1) It is not easy to squeeze the sap out of the plant tissue, 2) The sap needs to be diluted to fit into the analytical range of the test, and 3) The moisture content of the tissue needs to be accounted for somehow for the results to be most accurate.

Soil tests were developed in the 1930's as a guideline for phosphorus fertilizer application. The phosphorus soil test for the calcareous soils in the Western U.S. is based on bicarbonate extraction and is often called the Olsen P method. Phosphorus fertilizer recommendations for small grains based on this test are remarkably similar across the Western states. Despite the availability of this test, its proven accuracy (93% in California), and its low cost ($1 /acre), most farmers in Arizona apply phosphorus fertilizer to their small grains crops without the benefit of a preplant soil test. The purpose of this study was to demonstrate the effectiveness of the soil test in predicting a response to phosphorus fertilizer. At Maricopa, the soil test P was 8.1 ppm, a variable response to P fertilizer was expected, and a variable response to P fertilizer was obtained. We were able to detect a response to P fertilizer at this site with only 1 out of 4 varieties, and the response averaged across varieties was 336 lbs /acre or a 6% increase. No response to P fertilizer was obtained on a commercial farm in Buckeye where the soil test P was 22 ppm and a response was not expected. At the Yuma-Mesa site, the preplant P level was also 22 ppm, and a yield increase of29% (1442 lbs /acre) was measured on barley even though a response was not expected. The soil on the Yuma -Mesa is 95% sand and perhaps the soil test for P needs to be adjusted for this soil type, but at the other sites tested, the current soil test recommendations for P seem to be accurate.

Bread wheat and barley were seeded in low phosphorus soils which had had varying rates of ammonium phosphate-sulfate (16-20-0) applied. Statistical increases in yield were seen in the wheat study. The increased bottom line with the lowest rate of phosphorus declined as rates of phosphorus increased. Low crop values and high fertilizer costs made high application rates uneconomical. Barley yields were not statistically increased with the addition of phosphorus and the economics of applying phosphorus for this crop were negative. A two year summary is included in this report.

Yields of both wheat and barley were increased with the addition of nitrogen and the largest gain was seen when it was applied at the initiation of growth or at boot stage. Effects of applied nitrogen were somewhat masked by the addition of nitrogen through the use of well water. Nitrogen level in the well water added 21 pounds of nitrogen per acre foot of irrigation, adding 48 pounds of nitrogen throughout the growing season. With the low value of grain and the given cost of nitrogen fertilizer, added nitrogen did not increase profitability for the producer.

The economic effect of applying phosphorus at planting of durum wheat is directly correlated to the phosphorus that is available to the plants from the soil. In 1998 a study was done on a field with a bicarbonate soluble phosphorus level of 4.8 ppm, an a sizeable return on the phosphorous fertilizer investment was seen. In 1999 the test field had a phosphorous level of 13.0 ppm and as the University guidelines indicated, returns on phosphoroud expenditures were small. Negative returns were seen with barley and an increase of $61/ac was seen with 400 pounds of 16-20-0 on wheat.

Proper nutrient management is necessary for successful production of durum wheat in the desert. If grain protein content is less than 13 %, significant economic losses to growers can result. Late season nitrogen (N) fertilization can resolve this problem, but tissue test guidelines have not yet been established. The objectives of this study were to: (i) correlate NO₃-N in dried stem tissue with sap NO₃-N, (ii) determine the minimum NO₃-N concentration in lower stem tissue at heading associated with the critical grain protein content, and (iii) determine whether flag leaf head, or whole plant total N at heading can be used as indicators of N status. In November 1998 three varieties of durum wheat, Mohawk, Kronos, and Westbred 881, were planted at the Maricopa Agricultural Center. Five N rates (0, 100, 200, 300, and 400 lbs/A) were applied in four split applications. Each treatment was replicated three times in a randomized complete block design. Samples were collected from the lower stem, flag leaf head, and whole plant from each plot at heading and analyzed for total N. Grain yields ranged from 1937 to 6174 lbs /A for Mohawk, 1706 to 6161 lbs/A for Kronos, and 864 to 5162 lbs/A for Westbred 881. Grain protein content averaged 5.7% to 14.0% for Mohawk, 7.3% to 13.7% for Kronos, and 7.9% to 14.5% for Westbred 881. Correlation coefficients between stem NO₃-N and sap NO₃-N were 0.88 for Mohawk, 0.94 for Kronos, and 0.98 for Westbred 881. The critical NO₃-N concentration in the sap associated with >13% grain protein was 550 -770 ppm at heading for three varieties. Lower dried stem tissue critical NO₃-N concentration for Kronos was 4500 ppm NO₃-N, 4700 ppm NO₃-N for Mohawk, and 3600 ppm NO₃-N for Westbred 881 for a grain protein content of 13 %. Nitrogen concentration in flag leaves, heads, and whole plants were highly correlated with N rate. Therefore, N concentration in these tissues could potentially be used as indicators of late-season N status.

Malting barley is not a widely planted crop in the Southwest, due to grain protein contents that can sometimes exceed the industry standard of 11.4 %. To achieve < 11.4% grain protein, careful nitrogen (N) management is needed. Tissue testing guidelines for N management for reduced grain protein and acceptable yields have not yet been determined for malting barley in the Southwest. The objectives of this study were to: (i) correlate NO₃-N in dried stem tissue with sap NO₃-N, and (ii) develop stem NO₃-N guidelines for N management in malting barley. In November 1998 two varieties of malting barley, Morex and Crystal, were planted at the Maricopa Agricultural Center. Five N rates (0, 60, 120, 180, and 240 lbs/acre) were applied in four split applications. Each treatment was replicated three times in a randomized complete block design. Samples were collected from lower stems at the 3-4 leaf 2 node, and flag leaf visible growth stages. Grain yields ranged from 1011 lbs/A to 2677 lbs/A for Morex and 827 lbs/A to 2641 lbs/A for Crystal. Grain protein ranged from 6.94 -11.5% (Morex) and 8.48-13.0% (Crystal). Correlation coefficients between stem NO₃-N and sap NO₃-N were 0.83 for Morex and 0.85 for Crystal. For Morex and Crystal, grain protein was within the malting industry grain protein range of 10.5-11.4% and yield was optimized at 180 lbs N/A. Sap NO₃ analysis can be a useful tool for determining N status of malting barley.