1. A method comprising: receiving over a network at an agricultural intelligence computing system comprising one or more processors and digital memory, electronic digital data comprising a plurality of values representing crop data, soil data, and weather data for one or more fields; using digitally programmed logic in a temperature module of the agricultural intelligence computing system, creating and storing in computer memory a first digital model of temperature of soil in the one or more fields over a particular period of time based, at least in part, on the plurality of values representing crop data, soil data, and weather data; using digitally programmed logic in a hydrology module of the agricultural intelligence computing system, creating and storing in the computer memory a second digital model of water flow through the one or more fields over the particular period of time based, at least in part, on the plurality of values representing crop data, soil data, and weather data; using digitally programmed logic in a crop module of the agricultural intelligence computing system, creating and storing a third digital model of an uptake of water of one or more crops on the one or more fields over the particular period of time based, at least in part, on the modeled water flow through the one or more fields and the plurality of values representing crop data, soil data, and weather data; using digitally programmed logic in the crop module of the agricultural intelligence computing system, creating and storing a fourth digital model of an uptake of a nutrient of the one or more crops on the one or more fields over the particular period of time based, at least in part, on the plurality of values representing crop data, soil data, and weather data; using digitally programmed logic in a fertility advisor module of the agricultural intelligence computing system, creating a fifth digital model of nutrient availability in the one or more fields over the particular period of time based, at least in part on the first digital model of temperature of soil, the second digital model of water flow, the third digital model of the uptake of water of the one or more crops, the fourth digital model of the uptake of the nutrient of the one or more crops, and the plurality of values representing crop data, soil data, and weather data for the one or more fields by: computing an initial nutrient availability at an initial point in time comprising a portion of the nutrients in the soil that the crop is capable of accessing over the particular period of time as a function of initial nutrient levels in the soil, initial soil composition, and initial soil moisture; computing uptake of the nutrient by the one or more crops over the particular period of time; computing nutrient loss over the particular period of time to the atmosphere; computing nutrient loss over the particular period of time through leaching; for a particular point in time in the particular period of time, modeling an amount of the nutrient in the soil that the crop is capable of accessing and utilizing as the initial nutrient availability minus nutrient loss between the initial point in time and the particular point in time and nutrient loss to the atmosphere and through leaching before the uptake of the nutrient by the one or more crops over the particular period of time after the particular point in time; using a mobile device interface module, based, at least in part, on the fifth digital model of nutrient availability, causing display on a field manager computing device of a nutrient availability graph which indicates at least: a current modeled nutrient availability for the one or more crops of the one or more fields computed from the fifth digital model of nutrient availability; and a modeled projected future nutrient availability for the one or more crops computed from the fifth digital model of nutrient availability.