Organic vegetable farming revitalizes intensively-cropped soils

Continued use of organic fertilizer improves soil quality and in the long run gives crop yields that are at par with those of chemical or synthetic fertilizers. Colting and Bernard (BSU) verified these findings in their research conducted from 1993 to 1999.

Findings

• The first phase of the study (1993-1996) consisted of the following fertilizer treatments: (T1) control – no fertilizer; (T2) pure inorganic fertilizer consisting of 14-14-14, urea, 0-20-0, an 0-0-60 at rates based on the general fertilizer recommendation for each crop; (T3) 3 t/ha unprocessed chicken manure + inorganic fertilizer at ½ recommended fertilizer rates; (T4) 4 t/ha unprocessed chicken manure; and (T5) 8 t/ha unprocessed chicken manure. The evaluation was done in two different cropping systems, namely: Crop sequence 1 (CS1) snap bean-potato-green pea –snap bean; and Crop sequence 2 (CS2) cabbage-green pea-carrots-snap bean.
• The first phase results showed that in a four-year period, crop yields from organic fertilizers gradually leveled with crop yields from inorganic fertilizer. For the first three years, there were observed differences in crop yields among the fertilizer treatments. But on the fourth year, crop yields from the organic fertilizer treatments and those from the inorganic fertilizer treatments were all comparable.
• In the second phase (1997-1999), the fertilizer treatments were as follows: (T1) 4 t/ha unprocessed chicken manure + inorganic fertilizer at ½ recommended fertilizer rates; (T2) 8 t/ha unprocessed chicken manure; (T3) 4 t/ha processed chicken manure; (T4) 8 t/ha formulated garden compost; and (T5) 8 t/ha mushroom bed compost. The assessment was done in two cropping sequences: CS1, green pea-potato-cabbage, and CS2, potato-green pea-potato.
• Similarly, as in the first phase, crop yields from all of the fertilizer treatments were not significantly different from each other.
• Three years of continued use of organic fertilizers resulted in a reduction of soil acidity. The soil pH in 1997 ranged from 4.1 to 4.7, while in 1999, the resulting pH ranged from 5.2 to 6.2. In addition, the soil organic matter (OM) content increased from 2.03% in 1997 to 3.02% in 1999.
• The results from these trials indicated that in the long run, organic fertilizers could replace the synthetic inorganic fertilizers completely.

Source: PCARRD, 2001. Highlights 2000, Los Banos, Laguna.

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