Effect of integrated forage rotation and manure management on yield, nutrient balance and soil organic matter

This paper reports results from a field experiment established in 1995 and still on going. It is located in Lodi, in the irrigated lowlands of Lombardy, Northern Italy. The experiment compares two rotations: the annual double cropping system, Italian ryegrass + silage maize (R1); and the 6-year rotation, in which three years of double crop Italian ryegrass + silage maize are followed by three years of alfalfa harvested for hay (R6) Each rotation have received two types of dairy manure: i) farmyard manure (FYM); ii) semi-liquid manure (SLM). The intent was to apply to each unit land area the excreta produced by the number of adult dairy cows sustained, in terms of net energy, by the forage produced in each rotation, corresponding to about 6 adult cows ha-1 for R1 and 4 adult cows ha-1 for R6. Manure was applied with (N1) or without (N0) an extra supply of mineral N in the form of urea. The objectives of this study were: i) to assess whether the recycling of two types of manure in two forage rotation systems can sustain crop yields in the medium and long term without additional N fertilization; ii) to evaluate the nutrient balance of these integrated forage rotations and manure management systems; iii) to compare the effects of farmyard manure and semi-liquid manure on soil organic matter. The application of FYM, compared to SLM, increased yield of silage maize by 19% and alfalfa by 23%, while Italian ryegrass was not influenced by the manure treatment. Yet, silage maize produced 6% more in rotation R6 compared to rotation R1. The mineral nitrogen fertilization increased yield of Italian ryegrass by 11% and of silage maize by 10%. Alfalfa, not directly fertilized with mineral nitrogen, was not influenced by the nitrogen applied to the other crops in rotation. The application of FYM, compared to SLM, increased soil organic matter (SOM) by +37 % for the rotation R1, and by +20% for the rotation R6. Conversely, no significant difference on SOM was observed between R1 and R6 with the application of SLM. However, the maize stover used for composting FYM was produced by crops not included in the rotations R1 and R6, consequently the increase of soil carbon was counterbalanced by a deprivation of carbon in other land areas.