A long term field study explored the P status and decline of some of the more common agricultural soils in the Emilia Romagna region of Italy. The regional government provided financial support. A large percentage of soils in the region exhibits abundant P reserves accumulated over many decades through a widespread practice of P fertilization. The high level of these reserves nullifies the role of any further P application. The aim of the study was to ascertain for how long such soils which were rich in Olsen P (P extractable in NaHCO3 0.5 M, at pH 8.5) could sustain the same level of crop yield without P fertilization as compared to soils which received yearly doses of P fertilizer. Three soil types were examined: (i) a subalcaline clay-loam that is located near Quarantoli (Mirandola, Modena) and that is classified either as fine silty over clayey, mixed, mesic (Aquic) Udifluventic Ustochrept (Soil Taxonomy, 1992) or as Calcaric Cambisol (FAO - UNESCO, 1988); (ii) a subalcaline silty-clay that is located near Taneto (Gattatico, Reggio Emilia) and described either as fine, mixed, mesic Udertic Ustochrept or as Haplic Cambisol; (iii) a silty-loam, with shifting pH from acid to subalcaline, that is located near Gariga (Podenzano, Piacenza) and that is classified either as fine silty, mixed, mesic Udic Ustochrept or as Eutric Cambisol. The original research plan was to cultivate the three more common crops in the region - maize, soft wheat and lucerne - once the soil P status would prove to be inadequate. This event never occurred during the first ten years of the study. At the beginning of the experiment, maize was selected as the most suitable crop for removing P and accelerating the decline of soil P availability. At Gariga, only maize was cropped for the duration of the experiment. At Taneto, the cropping sequence was six years of maize followed by four years of lucerne. At Quarantoli, the three planned crops were sown beginning at different dates; hence, maize was cropped for ten years, lucerne for six years, and soft wheat for five years. Sudan grass was sown as a transition crop from maize to wheat. At all three locations, the following fertilizer treatments were compared: P 0 (control), P 1 (26.2 kg P ha 1 year 1) and P 2 (52.4 kg P ha 1 year 1). In the unfertilized plots, Olsen P concentration progressively decreased as a consequence of crop uptake. At Quarantoli, it went from an initial 19.3-23.8 mg kg 1 to a final 8.3-9.2 mg kg 1. The three crops induced a differential decline within an interval of 10-15 mg kg 1. At Taneto, the Olsen P values went from 23.2 to 10.2, with a reduction of 13 mg kg 1. At Gariga, a smaller decline (7.7 mg kg 1) was detected, from an initial 32.2 to a final 24.5 mg kg 1. At none of the experimental sites, Olsen P concentration was reduce sufficiently to cause a stable low-level yield. Bulking all the harvests of maize and wheat, and all the cuts and total DM of lucerne, the yield of P 0 was seldom significantly different from that of the P 1 and P 2 treatments. There were only 9 (out of 149) significant events, with lucerne claiming 8 of them. A slightly higher number of significant differences among P treatments was recorded for P concentrations in plants and for P removal in harvested DM. P concentrations were different in 16 (15 due to lucerne) out of 108 events. The rate of P removal by harvested crop was statistically different in 29 out of 149 cases. Again, lucerne was once more the sensitive crop in 22 cases. For the three soils, the declining function over time of available Olsen P was specified by the exponential equation: ln P = a + bt, where P is Olsen P in the 0-30 cm layer of soil, a and b are fixed parameters and t is time in years. Such equation summarizes the kinetic process of P supply depletion.
|Translated title of the contribution||[Autom. eng. transl.] Reuse of phosphate reserves in some types of Emilian soil - Long-term agronomic tests|
|Number of pages||170|
|Publication status||Published - 1997|
- P Olsen
- fertilizzazione fosfatica
- phosphatic fertilization
- soil phosphorus