Evaluation of Compost Leachates for Plant Growth in Hydroponic Culture

Abstract

Compost run-off leachates are usually rich in nutrients and can potentially be recycled in plant culture. Seedlings of tomato (Lycopersicon esculentum Mill. ‘Roma VF’) and marigold (Tagetes erecta L. ‘Crackerjack’) were grown for five weeks in each of six hydroponic treatment solutions: full and half strength Hoagland's solution; leachates from spent mushroom compost (SMCL) and pond-collected runoff from a commercial composting operation (RCL); and these leachates amended with extra nitrogen (N) and phosphorus (P) (SMCL+NP and RCL+NP, respectively). The leachates were low in content of N and P, but rich in potassium (K), magnesium (Mg), calcium (Ca), sodium (Na), and various microelements. Top dry weight of tomato seedlings was highest in the two Hoagland's solutions, intermediate in RCL+NP, and lowest in the other solutions. With marigold, top dry weight in SMCL+NP was similar to that in the two Hoagland's solutions, intermediate in SMCL, and lowest in the RCL+NP and RCL solutions. The poor tomato performance on the SMCL+NP regime was the result of a high proportion of NH₄-N ( < 50%), which over time lowered pH and caused nutritional disorders. Imbalance in tissue nutrient (low content of N and P and high content of K, Mg, Ca, and Na) from plants grown in the unamended SMCL and RCL solutions indicates a need to balance these nutrients in the leachates before it is recycled.

keywords:

• compost leachate
• hydroponic culture
• nutrient balance
• recycling irrigation water

Notes

^zmacronutrient salt source: NH₄H₂PO₄, KNO₃, CaNO₃, MgSO₄.

^ymeans of triplicate samples ± SD.

^xfrom NaCl.

^w0.6 and 0.3 mg L^{− 1} weekly, respectively.

^{Z **}

^* Significant at P < 0.01, and P < 0.05, respectively.