A.S. Gill ([email protected])
Several researchers have attempted to study the impacts of trees planted on field boundaries on the yield of food crops. However, not much information is available in the semi-arid and sub-tropical regions. Hence, a field trial was established at the research farm of the National Research Centre for Agroforestry, Jhansi (UP) in Central India from 1989 to 1990. The field trial determined the impacts of Acacia tortilis and Leucaena leucocephala, planted on field boundaries, on field crops under irrigated conditions.
Fig. 1. Grain yield of groundnut (t/ha) under different row directions of trees (mean of three years).
Acacia tortilis (commonly known as Israeli babul) is one of the most common tree species in Africa and the Middle East. It produces high-quality fuelwood and charcoal and is a valuable fodder species.
Leucaena leucocephala (commonly known as Subabul), on the other hand, is a highly versatile plant, well known for its ability to produce fuelwood and forage, and its fast growth.
Fig. 2. Grain yield of wheat (t/ha) under the influence of tree row direction (mean of three years)
The soil type in the research farm was red gravelly sandy loam of poor texture and low fertility. A crop rotation of groundnut in the kharif season, followed by wheat in the rabi season, was used under partially irrigated conditions. Crops were raised as per the recommended package of practices.
Fig. 3. A. tortilis and L. leucocephala planted on the boundaries of a wheat field.
Tree growth data were recorded in June of each year from 1990 onwards. The trees were pruned to fifty percent of their height each June from 1992 onwards. Leaf and fuelwood yields, biometrics data and crop yields were also recorded. The trees were pruned to ensure that sufficient sunlight reached the crops. Relative grain yield was obtained based on the crop yield from the center part of the field. The trees and crops were planted according to the following patterns:
1. Trees planted in an east-west (E-W) direction with crops on the southern (S) side
2. Trees planted in a north-south (N-S) direction with crops on the western (W) side
3. Trees planted in an east-west direction with crops on the northern (N) side
4. Trees planted in a north-south direction with crops on the eastern (E) side
The average relative grain yield of groundnut (Fig. 1) and wheat (Fig. 2) was 93.3% when planted on the western side, with trees planted in a north-south direction. The relative grain yield of crops raised on the southern side with the trees planted in an east-west direction was 109.2%. The lowest yield was obtained from the groundnut and wheat planted on the northern side with the trees planted in an east-west direction. On average, trees grew best when planted in an east-west direction with the crops grown on the northern side.
The field trial demonstrated that the biomass production of nitrogen-fixing trees planted on the field boundaries enhanced soil fertility. This system increased the amount of organic carbon by 24.9%, available nitrogen by 29.6%, available phosphorus by 65.6% and available potash by 40.4% by the end of the third year. (The author is a principal scientist at the National Research Centre for Agroforestry, Jhansi, India.)
