Nutrient and crop management studies in irrigated cotton production systems

Increased efficiency in agricultural production is becoming increasingly important in the present economic climate. The three studies presented in this dissertation have been developed to help producers achieve a greater efficiency with respect to crop production. The first is the development of the cotton monitoring system (CMS). This software was developed as an end product to over ten years of research into cotton crop monitoring. It allows for the entry of crop growth and development data, along with other crop inputs. All growth indices are plotted against long-term baselines to indicate the crops status in relation to normal growth patterns. Other University of Arizona extension publications are available that are directed at helping the user interpret the data and how best to use it in making management decisions. The second project involves the evaluation of added nitrogen interaction (ANI) effects in irrigated cotton. This was accomplished by comparing two methods of determining nitrogen recovery efficiencies (NREs), the difference technique and the isotopic dilution technique. No differences were observed between the two methods in the first year, 1997 indicating the absence of a ANI. However in 1999, differences were observed between the two methods due to abnormally high vegetative growth experienced by the crop which resulted in increased root growth and subsequent exploration of the soil and an increased uptake of soil N. The third and final project was conducted to examine the loss of N from several different sources of irrigation water around the state of Arizona and to observe the effects of temperature on this process (25, 30, 35, and 40°C). Ammonium sulfate was added to a 350 mL volume of water from which aliquots were drawn at specific time intervals and analyzed for NH₄⁺-N. In a 24 hour period up to 90% of the added N was lost at 40°C). In general, as soluble salts increased the rate at which NH3 was volatilized also increased. The results from this study indicate the need to consider potential N losses from irrigation water when making decisions regarding N fertilizer management