Accumulative Effects of Manure and N on Continuous Corn and Clay Soil. II. Chemical Changes in Soil

Continuous corn (Zea mays L.) was grown on a Panton clay soil (Typic Ochraqualf). Four rates of manure (0, 22, 44, and 66 tons/ha) and five rates of N (0, 56, 112, 168, and 224 kg/ha) were combined in a factorial arrangement and applied each year to the same plots. Also, 120 kg/ha of P and 90 kg/ha of K were applied for 4 years to all plots. Maintenance of structure and fertility had been difficult in this soil. It had not been intensively cultivated even though it lay in large, level fields. The objectives were to study the effects of the treatments on growth, yield, and nutrient uptake of corn and on the physical and chemical properties of the soil over a period of 5 years (six crops). Results of the first objective have been previously published (7) and effects chemical properties will be reported here. Cultivation and cropping for 5 years on the check plots reduced organic matter; (by N) 8.7% and OM (by 17.7%. An annual application of 44 tons/ha of fresh dairy cattle manure was needed to maintain soil OM. CEC was increased by manure treatments as would be expected from increase in soil OM. Soil test results (pH 4.8, NH₄OAc extractions) showed that P from manure was more available than fertilizer P; 119 kg/ha of P from manure increased soil test P about the same as 480 kg/ha of P from fertilizer. However, K, either from manure or fertilizer, was readily fixed by the soil (60 to 75% of the applied). More than 414 kg/ha of K was needed to bring K potential in soil to the −3,500 calorie level suggested as adequate for standard free energy of exchange of K for Ca and Mg (13). Manure application up to 44 tons/ha did not contain enough Ca or Mg to maintain initial levels in the soil. Manure and N treatments had no measurable effects on Fe and Na levels in the soil. Averaged over all treatments, exchangeable Na decreased from 123 to 85 kg/ha and Mn from 45 to 20 kg/ha during the 5 years (1966 to 1971). Treatments of N did not affect rate of breakdown of OM nor decrease pH. The highest rate of N, compared to check plots, slightly increased Mn extracted (by 6 kg/ha). The highest rate of manure decreased extractable Mn (8 kg/ha) and AI (5 kg/ha). These data showed the value of fresh manure as a soil amendment in addition to its nutrient content. Land applications of manure should be encouraged as a method of disposal but its agronomic value emphasized to encourage use with a minimum of loss.