Use of a Modified N-Expert System for Vegetable Production in the Beijing Region

Abstract

A series of field experiments were conducted over a three-year period to test a modified N-Expert system (the decision support system for nitrogen recommendations) with different irrigation regimes for a rotation of amaranth (Amaranthus tricolor L.), spinach (Spinacia oleracea L.), and cauliflower (Brassica oleracea L.). Local commercial fertilizer practice based on farmer surveys was selected as the control, and irrigation treatments followed conventional practice with a balanced irrigation schedule. Some parameters, notably target yields and net mineralization rates, were modified according to local conditions, and most were referenced from the database of the N-Expert system in the first cultivation year of the rotation. Parameters were tested in earlier field experiments and were fine-tuned in later experiments. No significant yield reduction occurred below conventional nitrogen (N) practice using the recommended N treatment (N2) with different water treatments, except for irrigation treatments between 60% and 90% of PESW (plant extractable soil water: the difference between field capacity and wilting point) in 2000 and conventional irrigation practice in 2001 for cauliflower. There was a significant decrease in residual N_min at harvest in treatments using the modified N-Expert recommendation system compared with conventional N practice. This indicates that there is considerable potential for use of the N recommendation system for sustainable vegetable production in the North China Plain.

Keywords:

• N recommendation
• vegetable growth
• Beijing region
• N-Expert system
• soil N_min

ACKNOWLEDGMENTS

We thank the Natural Science Foundation of China (No. 3023250) and the Sino-German Project funded by Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF, No. 0339712A), Germany, for financial support, and Drs. Matthias Fink and Carmen Feller, Institute for Vegetable and Ornamental Plants (IGZ), Grossbeeren, Germany, for their helpful advice in using the N-Expert system.

Notes

^a No basal fertilizers or organic manure were applied to amaranth.

^b Composition (total NPK): 1.7% N, 4.1% P₂O₅, and 2.29% K₂O in 1999 and 2000, and 1.5% N, 4.1% P₂O₅, and 2.75% K₂O in 2001.

^c Applied as calcium monophosphate.

^d Applied as KCl in 2000 and K₂SO₄ in 2001.

^a No defined water treatment for amaranth. On July 18, 1999 about 30 mm water was supplied for all irrigation treatments; 11 mm water was then supplied for W1 on July 27, 1999.

^a W1, Conventional irrigation practice; W2, 50–80% of PESW; W3, soil water tension; N1, conventional N fertilizer application rate; N2, N-Expert system N recommendation; and N3, 80% of N-Expert system N recommendation.

^a Within each row, mean values with a letter in common are not significantly different at the 5% level by Duncan's multiple range test.

^a W1, Conventional irrigation practice; W2, 50%–80% of PESW; W3, soil water tension; N1, conventional N fertilizer application rate; N2, N-Expert system N recommendation; and N3, 80% of N-Expert system N recommendation.

^a Target safety margin at harvest.