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Plant Response to Fish Farming Wastes in Volcanic Soils

Centro Regional Universitario Bariloche, Univ. Nac. del Comahue, 8400 Bariloche, Argentina;
Area Conservación del Medio Natural (C.I.T.-I.N.I.A), Madrid, España.

^* Corresponding author (rvtomas{at}criba.edu.ar).

ABSTRACT

Agricultural use of aquaculture wastes appears to be a sound ecological and economical means to improve soil fertility and to decrease the potential for adverse water quality impacts in South Argentina. A 3-mo greenhouse experiment with ryegrass (Lolium perenne L.) was conducted to determine plant availability of N and P from aquaculture wastes and compare results with previous laboratory incubations. Treatments included: (i) wastes taken from sediments under cages in a 3-yr-old fish farm (EA) applied at 40 and 80 Mg ha^–1; (ii) wastes taken from sediments under cages in an 8-yr-old farm (LM), applied at 10 and 20 Mg ha^–1; (iii) the lowest waste rates amended with 50 kg ha^–1 synthetic N; (iv) four synthetic fertilizer treatments including a single N rate of 80 kg N ha^–1 and four P levels of 30, 40, 60, and 80 kg P ha^–1, and (v) a no-fertilizer control. Although total N and P were higher in LM than in EA, and N mineralization rates in lab incubations were similar (13%), ryegrass yields and N uptake were much higher in EA than in LM. When mineralized N was estimated as the difference between added N and total N uptake, values were 50 to 63% for EA and 5 to 14% for LM. Ryegrass yields were approximately as follows: EA > FI > LM > Control. Synthetic fertilizer treatments showed the lowest values of P utilization efficiency, residual Olsen-P in soil and plant P uptake in biomass, and the highest P retention in soils. The lowest waste rates with addition of N produced comparable ryegrass yields with the highest rates. Results emphasize: (i) the need to include living plants in mineralization potential evaluations to avoid significant errors in nutrient cycling models, and (ii) the importance of organic amendments in ameliorating plant P availability in high P-fixing volcanic soils.