Using the reasoned nitrogen (N) fertilization method in potato crops (Solanum tuberosum L.) requires the validation of its parameters under the probable conditions of crop response. A field experiment in an Andisol was established to assess the parameters of this method and the nitrogen utilization efficiency of the crop. To describe the crop N response, five statistical models were used. Dry matter production and nutrient concentration were measured in tubers, leaves, fruits and roots. At both the beginning and the end of the experiment soil samples were collected to evaluate the mineral N. The quadratic-potential model was the most appropriate to describe the positive response of the potato crop to available nitrogen, from an initial level of nitrogen (the control, zero application ) to a maximum application of 200 kg N ha^-1. The relationship between the N doses and the potato yield reached a physical optimal of productivity at a rate of 228 kg N ha^-1. Higher rates (300 kg N ha^-1) resulted in a decrease in yield, generating phytotoxicity for cultivation. This variation allowed us to evaluate the reasoned application method under different nitrogen availabilities (deficiency, optimal and above-optimal) in addition to the variation of the parameters generated.

The residual value of phosphorus addition is described by two reactions: a quick initial reaction followed by a slower reaction over time. In this study, the residual effect of two P sources was evaluated: monopotassium phosphate (MKP) and triple superphosphate (TSP) added to soils from Ecuador and Chile with contrasting soil P retention capacity. Olsen-P extractability was measured and compared in soil samples 1, 2, 4, 8, 15, 45, 90, 180 and 360 days after the addition. The Olsen-P extracted at 24 hours after the P addition varied among soils, and extracted between 10 and 66% of the P added depending upon the soil, with lower extraction values in soils with high P retention capacity. When the source was TSP, only approximately 70% of P was extracted compared to that extracted when MKP was added. After the phosphate addition there was a clear initial effect followed by a progressive loss of Olsen-P extractability. Furthermore, over time, a state of quasi-equilibrium or a stationary state become evident in which the loss of P extractability was minimal. When the initial effect was removed, as a point that characterizes different types of soils, the loss of P extractability was similar among soils, and reflects the amount of phosphate added despite the type of fertilizer used.

Urea present in cattle urine contributes large amounts of nitrogen (N) to grazed pastures, which can be the equivalent to approximately 1000 kg N ha⁻¹. However, there are no studies in volcanic soils of southern Chile on the effect of different concentrations of urinary N deposited in the soil, nor of the effect different wetting and drying conditions mimicking the variation in weather conditions on the nitrification process from urea to NH₄⁺ and total oxidized nitrogen (TON) over time. In addition, the inhibition of nitrification driven by the accumulation of NH₃ at high rates of N applied to Andisol has not been evaluated. Fresh cattle urine was applied at three different rates of N equivalent to 247 kg N ha⁻¹ (Low N), 461 kg N ha⁻¹ (Medium N), and 921 kg N ha⁻¹ (High N), as well as deionized water as a control. Further, three moisture conditions were imposed: constant moisture (CM), drying–rewetting (DRW) cycles at 7-day intervals, and soil drying (SD). Destructive soil core samples were evaluated for top and bottom halves individually every 7 days over a 36-day period to measure changes on inorganic N and pH. There were no interaction effects for N rates and soil moisture. The main effect of the different rates of N on mineralization was significant throughout the incubation period, while the effect of the different moisture conditions was variable over time. High N was associated with elevated NH₃ concentrations and could explain why total N mineralization was partially inhibited. These results suggest that the presence of different nitrifying microorganisms in soil under different chemical and physical conditions determines nitrification, and thus, the oxidation of ammonia should be studied in more detail as the first step of nitrification, specifically in volcanic soils.