Integrated cropping systems for year-round intensive vegetable production in the lowland tropics
Volker Kleinhenz
This activity aims to study the reduction of seasonal variation in vegetable production in tropical, rice-based lowlands through permanent high beds and introduce the Nmin method to maintain productivity, but minimize N-fertilizer application and reduce nitrate leaching.
From 1993 to 1995, the feasibility of permanent high beds (50 cm high) and Nmin-method (reduction of the N-fertilizer rate by the amount of soil-NO3 before application) was compared to standard practices (2025-cm-high flat beds and the recommended N-fertilizer rate) in intensive, year-round vegetable production of four species (table 2).
Table 2. Marketable yield (kg/m2) of vegetables as influenced by different bed heights (flat bed, high bed) and fertilizer rate (Nmin, standard) |
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1993 |
1994 |
1995 |
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Chinese cabbage |
Chili |
Carrot |
Veg. soybean |
Chinese cabbage |
Chili |
Carrot |
Veg. soybean |
Chinese cabbage |
Analysis of variance |
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Flat bed |
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Nmin |
1.49a |
0.20a |
1.40a |
1.19a |
0.19a |
0.07a |
3.00a |
0.88a |
1.80b |
Standard |
1.37a |
0.22a |
1.29a |
1.26a |
0.75a |
0.17a |
3.06a |
0.89a |
2.43a |
|
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High bed |
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Nmin |
2.14a |
0.53b |
1.16a |
1.05b |
1.32b |
0.29b |
2.99b |
1.28a |
1.32b |
Standard |
2.10a |
0.62a |
1.10a |
1.10a |
1.99a |
0.36a |
3.24a |
1.31a |
3.07a |
|
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Comparison, probability of no difference |
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High bed vs. flat bed |
<0.01 |
<0.01 |
0.13 |
<0.01 |
<0.01 |
<0.01 |
0.43 |
<0.01 |
<0.01 |
Nmin vs. standard |
0.31 |
0.04 |
0.39 |
0.06 |
<0.01 |
<0.001 |
<0.001 |
0.23 |
<0.01 |
Permanent high beds successfully alleviated the negative impacts of overwet soil conditions in the rainy season. Crops developed profound root systems and absorbed available soil nitrate effectively. Consequently, yields were significantly higher compared to traditional flat beds, and less nitrate leached below the root zone. Rainy season conditions induced water stress and shallow root systems on flat beds. Water stress in the rainy season and accumulation of soil nitrate during the dry season with negligible leaching were responsible for the success of the Nmin-method on flat beds. About 600 kg or 56% N was saved without significantly affecting yields, but reducing nitrate leaching. The greater biomass and yield potential of vegetables could, however, not be sustained with the Nmin-method on high beds.