Search

A two year field study (1996/97 and 1997/98 growing seasons) was carried out at the Maricopa Agricultural Center (33º04'07" N; 111º57'18" W) of the University of Arizona, USA, to investigate the water use and to derive Kc's for subsurface drip-irrigated head lettuce grown in small weighable lysimeters. Measurement periods ranged from 480 to 1100 ºC-day (96/97) and from 439 to 1098 ºC-day (97/98). These intervals corresponded essentially to the second half of the crop cycle which amounted to a 1100 ºC-day, on average. The lysimeters were weighed periodically and the computation of the water balance revealed an average water use of 117 mm. Basal crop Kc was expressed as a function of cumulative growing degree days following a multiple linear regression procedure in which the data were fitted with a Fourier sine series model with up to six coefficients. Two-year Kc curves were obtained based on the Hargreaves, FAO Penman and FAO Penman-Monteith equations and compared to the AZSCHED (AriZona SCHEDuling) irrigation package. Predicted Kc peaked 0.88, 0.80 and 0.81 with the Hargreaves, FAO Penman, FAO Penman-Monteith equations, respectively, in the range of 1000 to 1050 ºC-day, in contrast to AZSCHED which predicted the peak Kc to be 1.01 at 1150 ºC-day.

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