25. Mechanisms for overyielding in a sunflower/mustard intercrop.
Agronomy J., 84, 1992, pp. 188-194
The objectives of this study were to verify the occurence of overyielding and to examine patterns of N and water use as possible mechanisms for over-yielding in sunflower/mustard intercrops. Secondary objectives were to examine the effect of N fertilizers and intercrop structure (planting pattern) on intercrop resource use and yield advantage. It is hypothesized that the lack of competition between species for a significant resource (the competitive production principle) was a cause of previously observed advantages in this intercrop system.
Two intercrop patterns and sole crops of mustard (Brassica hirta Moench) and sunflower (Helianthus annuus L.) were planted in 1988 and 1989 on a silt loam soil to examine mechanisms for overyielding in this intercrop system.
A strip intercrop pattern where 2.28-m strips of sunflower (76-cm rows) alternated with 2.28-m strips of mustard (15-cm rows) was compared with a more intimate row intercrop pattern of 76-cm sunflower rows interplanted with four 15-cm rows of mustard. Nitrogen was applied at planting at 0 or 112 kg N ha-1 to whole plots, with planting patterns allocated to subplots in a split-plot design. Soil water content, nitrate N, and total N were measured at different locations and depths in the intercrop and sole crop patterns during the growing season.
Mustard rows adjacent to sunflower in the strip intercrop yielded an average of 61% more than sole crop rows. Sunflower rows adjacent to mustard in the strip intercrop yielded an average of 40% more than sole crop rows. Yields of both sunflower and mustard were lower in the row intercrop compared with respective sole crops. Land equivalent ratios ranged from 0.96 to 1.43 in the strip intercrop and were generally below 1.0 in the row intercrop. Application of N did not consistently affect
LER. Soil depletion patterns indicated that border rows of mustard obtained both soil water and N from the strips planted to sunflower at a time when demand for these reources by sunflower was low. Sunflower border rows obtained water and N from mustard strips later in the season.
Concluding, intercropping, although an inexpensive technology, is an intensification of management. In the sunflower-producing areas of the northern Midwest of USA, extensive management practices are more common.
Although previous studies confirm that strip intercropping of the two species potentially could increase yield, few producers are currently using this technique. This may be due partly to the minor crop status of both crops in this region, but other Cruciferae, such as canola (Brassica napus L. or Brassica campestris L.), are also candidates for this type of strip intercrop system with sunflower.
The strip intercrop used in this study was narrower than would be practical for equipment used currently in the sunflower-producing regions of the USA.
Other management practices, such as tillage, weed control, diseases, insects, harvesting, and timing of agronomic practices, must also be considered. Mustard is a crop that requires a fine seedbed, and sunflower, though less exacting, is compatible with mustard in this respect. Both crops are planted early, although sunflower could be planted later in a strip arrangement.
There is no evidence in the field trials that disease or insect infestation differed in the intercrops compared with the monocultures.
In summary, there are potential yield and land-use advantages for the practice of strip intercropping but not row intercropping of sunflower and mustard. Complementary use of water and N over time are implicated as causes of overyielding exhibited by both species in this pattern. The creation of border areas between species through strip intercropping resulted in areas of excess soil N and water (compared with sole crops) that could be used by border rows of the companion crop during critical times of development, producing a border row yield advantage. This overyielding could be applied to mechanized systems if cropping intensification is wanted.
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Australia, field trial, intercropping, cassava, pigeonpea, agronomic practices, land equivalent ratio, crop productivity
CENPUKDEE, U. and S. FUKAI
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