Edward C. Martin

DEVELOPMENT AND TESTING OF A SMALL WEIGHABLE LYSIMETER SYSTEM TO ASSESS WATER USE BY SHALLOW-ROOTED CROPS

A mobile weighing system was designed in 1994 to weigh small lysimeters to measure water use by shallow-rooted crops. Using a reconditioned pesticide sprayer, a hoist, and a weighmeter, small lysimeters were weighed in the 1995, 1996, and 1997 growing seasons. The lysimeters were constructed of 4.8-mm hot-rolled steel and were 0.91 x 1.02 x 0.61 m in size with an internal area of 0.929 m 2 . The weight of a lysimeter containing only moist soil was 1.110.27 kg. At the beginning of each season of use, several tests were conducted on the weighing system to determine if it was sensitive enough to give adequate results of crop water use. In 1995, tests were conducted on linearity, repeatability, thermal shift, and creep errors. The values were ±0.062 kg, ±0.12 kg, -0.007 kg/ ° C, and -0.242 kg, respectively. The terminal linearity was 0.082 kg (1996) and 0.043 kg (1997). The measurement uncertainty decreased as the number of lifts increased. The results showed that the system was capable of producing adequate results for determining crop water use.

Water use and crop coefficient of subsurface drip-irrigated lettuce in Central Arizona

Um estudo conduzido na Fazenda Experimental Maricopa (33o0407 N; 111o5718 W), pertencente a Universidade do Arizona, USA, nos anos agricolas de 1996/97 e 1997/98, objetivou determinar o uso de agua e derivar coeficientes de cultura (Kc) da alface de cabeca irrigada por gotejamento subsuperficial e cultivada em lisimetros de pesagem intermitente. O periodo de medicoes, expresso em graus-dia acumulados, variou de 480 a 1100 oC-dia em 96/97 e de 439 a 1098 oC-dia em 97/98. Esses intervalos corresponderam a segunda metade do ciclo da cultura, sendo que ate a colheita somou-se uma media de 1100 oC-dia. Os lisimetros eram pesados periodicamente e o balanco hidrico revelou um consumo medio de 117 mm, naqueles periodos. O Kc basal foi relacionado com o acumulo de graus-dia atraves de regressao multipla, seguindo um modelo dado por uma serie seno de Fourier, com ate seis coeficientes. As curvas de Kc foram determinadas com base nos metodos de Hargreaves, FAO Penman e FAO Penman-Monteith, para calculo da ETo e comparadas por aquela gerada pelo programa AZSCHED (AriZona SCHEDuling) de manejo da irrigacao. Valores maximos de Kc estimados foram 0,88 (metodo de Hargreaves), 0,80 (FAO Penman) e 0,81 (FAO Penman-Monteith) no intervalo de 1000 a 1050 oC dia, inferiores a 1,01 em 1150 oC dia, que e o maximo Kc previsto pelo programa AZSCHED.

Application of animal manure/compost in an oat/corn rotation to assure compliance for CAFO nitrogen management in Arizona

This study was initiated to develop and assess the management of the application of animal waste nand compost to an oat/corn rotation in Arizona. Unlike many Eastern states, Arizona uses nitrogen as the nlimiting nutrient in animal waste applications. In this project, nutrient analysis for nitrogen, phosphorus and nelectroconductivity were conducted on soil, manure/compost, and plant samples. There were three treatments nreplicated four times in this study. Treatment 1: inorganic nitrogen sources; Treatment 2: manure; Treatment 3: ncomposted manure. All management decisions are made to maximize yield while assuring that the amount of nnitrogen applied was equivalent to the nitrogen removed in the crop. In the first year, there was little or no ndifference in crop yields. In the second year, yield differences began to show. The soil nitrate-N content was nremaining relatively low and equal between treatments. However soil phosphorus content has significantly nincreased in the manure and compost plots. According to the ruling, if the level of P becomes high enough, then nP will become the limiting nutrient. Thus far, we have not reached that point; however, P levels are being nmonitored closely.

APPLICATION OFANIMAL MANURE/COMPOST IN AN IRRIGATED OAT/CORN ROTATION

This study was initiated to determine the biological and nutrient impacts of manure and compost applications on an oat/corn rotation in Central Arizona. Bacterial analysis for E.Coli, Listeria and coliphage and nutrient analysis for nitrogen, phosphorus and electroconductivity were conducted on soil, manure/compost, irrigation water, drainage water and plant samples. The presence of endocrine disruptors was also tested on the irrigation and drainage water. After a single season of oats, there doesnt appear to be any significant increase in the presence of bacteria in the soil-water- plant environment. Endocrine disruptors were detected in drainage and irrigation water samples. Nitrate leaching is occurring but at relatively low rates. Oat forage yields between treatments were all over 10,000 kg/ha and there was no statistically significant difference between them.