Mapping Soil Chemical Properties and Nutrients in a Corn and Soybean Field.

Knowledge on the distribution of soil chemical properties and nutrients is important as it can help farmers to chose appropriate crop species and management practices to maximize field productivity while sustaining soil quality. The objective of this study was to map the distribution of selected chemical properties (pH, CEC, OM) and macro-nutrients (N (NO₃^- and NH₄⁺), P, K, Ca, S and Mg) from 0 to 60 cm depth in a corn and soybean field. The study was conducted at Lincoln University’s Freeman farm in a 10 acre field divided into 48 plots. The soil of the experimental site is Waldron silty clay loam. Soil samples were collected at four different depths: 0-10 cm, 10-20 cm, 20-40 cm and 40-60 cm in each of the 48 plots. After collection, the soil samples were air-dried and sent to a commercial laboratory for analyses for soil chemical properties and nutrients. Results showed that, on average, the pH(6.8) and OM (1.7%) were the same at all depths while CEC (15.00 meq/100g) decreased by one unit in 20-40 cm depth.  Average values for NO₃^-(14.67 ppm), K(131.67 mg/kg) and S(9.77 ppm) were higher in 0-10 cm and decreased in the remaining depths. Variogram analysis showed effective ranges of spatial variability (A_o) of 5 to 30 m for soil chemical properties and 4 to 57 m for soil nutrients, indicating that not all these properties could be sampled at a same distance.  Field maps also showed that each soil chemical property and each nutrient followed a particular distribution pattern across the field. These results, although preliminary can be useful in deciding how much and where to apply chemical fertilizers.