Agronomic considerations for different cropping system are different due to inclusion of more than one crop as in intercropping or sequence cropping system. Thus, principal involved in management of 1/c and sequence system are different.
Intercrop is practiced with two objectives:
1) To get additional yields through and intercrop as bonus and
2) To avoid risk.
Management of Intercropping Systems:
In intercropping system crops are grown simultaneously. Management practices aim to provide favorable environment to all the component, exploit favorable interaction among the component crops and minimize competition among the components.
1. Seedbed Preparation: The objective of land preparation is to establish an ideal zone for the seedling that minimizes the stress. Potential stress condition include inadequate or excess moisture, unfavorable temperature for a given species, soil crushing weeds, residue of preceding crop and insect or pathogen attack. Important of seedbed is the same in both conventional (monoculture) and in multiple cropping. Seedbed preparation depends on the crop. Deep rooted crops responds to deep ploughing while for most of cereal shallow tillage is sufficient. The crops with small seed required fine seedbed, cotton, and maize, planted on ridges, certain crops on flat seedbed. Since more than one crop in intercropping, the seedbed preparation is generally prepared as per the needs of base crop. Sugarcane planted in furrow and intercrop sown on ridges, certain crops on flat seedbed. Since more than one crop in intercropping, the seedbed preparation is generally prepared as per the needs of base crop. Sugarcane planted in furrow and intercrop sown on ridges. In Groundnut + red gram intercropping system, flat seedbed is prepared for sowing crops. However, ICRISAT is recommending broad bed and furrow for black soils. In rice + maize intercropping system, ridges and trenches are formed. Maize is planted on ridges and rice in trenches.
2. Varieties: The varieties of component crop in intercropping system should be less competing with the base crop and peak nutrient demand period should different from the base crop. Maturity period between two components is minimum of 30 days. Hybrids varieties of sorghum like CSH -6, CSH -9 are suitable for intercropping with long duration variety of red gram like C11 and LRG 30 because of wider gap between maturity periods. The varities selected for intercrop should be have thin leaves, tolerant to shading and less branching. If the base crop is shorter than intercrop, the intercrop should be compact with erect branching and its early growth should be slow. The characteristics of the base crop should be as in sole crop.
3. Sowing: practices of sowing are slightly altered to accommodate inter- crop in such a way that it cause less competition to the base crop. Widening inter row spacing of cereal component to accommodate more rows of component legume crop improves legume yield and efficiency of the intercrop system. Sowing of base crop is done either as paired row, paired – winder row or skip row of base crop are brought close by reducing inter row spacing. The spacing between two pairs of rows is increased to accommodate the inter crop. Such row arrangement of component crops within the rows improves the amount of light transmitted tio the lower component crop, which can enhance legume yield in cereal legume intercropping system.
For example – the normal row spacing of Rainfed is 30 cm the row spacing is reduce to 20cm between paired rows and 50cm spacing in two in two pairs. The spacing in paired row planting designed as 20/50 cm indicated that the spacing between two rows in pairs is 20 cm and among the pairs 50cm.
Similarly, pearl millet is planted with row spacing 30/60 cm in paired row planting. These changes in crop geometry do not alter the yield of base crop, but intercrops are benefited to some extent. Or when alternating pairs of sorghum rows 90 cm with two rows of an associated legume, Singh (1972) found that LER was greater compared at 60cm between rows with two rows of the legume in between Planting in fixed ratio of intercrop is most common. The intercropping system of groundnut + red gram is either in 5:1 or 7:1 ratio and sorghum + red gram in 2:1 ratio. In these cases the normal three tined or four seed drill can be used without any modification. The hole pertaining to intercrop row in the hopper is closed with a piece of clh in that row, intercrop is sown with alkali or kera.
For higher yields, base crop population is maintained at its sole crop population and intercrop population is kept at 80 percent of its sole crop population.
Relative sowing time of component crop is important management variable manipulated in cereal- legume me /C system but has not been extensively studied. Sowing may be staggered to increase the temporal difference, which might result in higher yield advantage. (Singh et el.1981).
4. Fertilizer Application: The nutrient uptake is generally more in intercropping system compared to pure crops. When the legume are associated with cereal crop in intercropping system, legume supplement a portion of nitrogen required of cereal crop; the amount may be of 20kg/ha by legumes. Application of higher dose of nitrogen to the cereal + legume intercropping system not only reduce the nitrogen fixation capacity of legumes, but also growth of legume is suppressed by aggressive cereals owing to fast growth of cereals with increased availability of nitrogen, cereal + legume intercropping, therefore is mainly advantageous under low fertilizer application.
Considering all the factors, it is suggested that the nitrogen dose recommended for base crop as pure crop is sufficient for intercropping system with cereal + legume or legume + legume. With regards to phosphorus and potassium, one eighth to one fourth of the recommended dose of intercrop is also added in addition to recommended dose of base crops to meet the extra demand. Basal dose of nitrogen is applied to rows of both components in cereal + legume inter crop. Top dressing of nitrogen is done only cereal rows. P & K are applied as basal dose to both crops.
5. Water Requirement: The technique of water management is the same for sole cropping and intercropping or sequential cropping. However, the presence of an addition crop may have an important effect on evapo- transpiration. With proper water management, it is possible to grow two crops where normally only one crop is raised under rain fed condition. Intercropping system is generally recommended for rain fed crop get the stable yields. The total water requirement of I/c dose not increase much compared to sole cropping. At ICRISAT, the water requirement of sole sorghum and intercropping with red gram was almost similar (584 and 585 mm, respectively). However in a more competitive crop like onion as intercropped in groundnut increase the total W.R by about 50mm. the total water used in intercropping system is almost same as in sole crops, but yields are increased. Thus water use efficiency of intercropping is higher than sole crops.
Scheduling of water: if one of the crop is irrigated based on its requirement, the other crop may suffer due to excess water stress, sometimes leading to total failure of crop. In cotton black gam I/C system, cotton is irrigated once in 15-20 days. The intercrop black gram is often affected by excess water and gives poor yield. In such situations, skip furrow method of irrigation is advocated. Scheduling irrigation at IW/CPE ratio of 0.60 to 0.80 or irrigation at one bar soil moisture tension is suitable for most of the systems.
6. Weed Management: Generally it is believed that intensive cropping reduce weed problems. Weed infestation depends on the crop, plant density and cultural operation done. Weed problems is less in intercropping system compared to the sole crops. This is due to more complete crop cover and high density available in I/C cause severe competition with weeds and reduce weed growth. The weed suppressing ability of intercrop is dependent upon the component crops selected, genotype used, plant density adopted, proportion of component crops, their spatial arrangement and fertility moisture status of the soil.
Experiment carried out at ICRISAT, Hyderabad, indicated that there was 50- 75 % reduction in weed infestation by intercropping. Pigeon pea + sorghum I/C system, which is extensively practiced in Karnataka, M.S and A.P is known to reduce weed intensity. The higher plant population used and also complete covering of the soil earlier in intercropping system reduces weed infestation. In late maturing crops that are planted wide rows, presence of early maturing crops helps to cover the maturing crops that are planted wide rows, presence of early maturing crops helps to cover the vacant inters row space and keeps weed under check.
Quick growing non- competitive, compact legumes like green gram and black gram act as another crop due to their good canopy coverage.
In certain situations, intercrops are used as biological agents to control weeds, black gram , geen gram, cow pea in sorghum and cowpea in banana reduce weed population and one hand weeding can be avoided by this method, however, in some intercropping system like maize + groundnut, rice+ tapioca, maize + tapioca, weed problem is similar to their sole crops. The growth habit of genotype used in intercropping has a great influence on weed growth. Weed infestation in I/C is influenced by early growth and competitive additives of the component crops. If one or both the component crops are vigorous and cover the land area rapid ally, weed infestation is greatly reduced. Early crop canopy to cover the soil is more important than rapid increase in plant height.
It is well known that, different species of weeds are associated with different crops, but weeds present in sole crops are different than those present in intercropping system. At Hyderabad, in pearl millet as sole crop mixed weed flora was observed as Celosia, Digit aria and Cupreous in sole crop of groundnut. In pearl millet + groundnut intercropping system type of weeds changes with proportion of component crops. As more rows of groundnut are introduced in place of pearl millet of rows, there is a striking increase in both numbers and biomass of the tall and competitive Celosia, especially in groundnut rows.
Weed problem is less; weed control is necessary in intercropping system. But labour required for weeding is less; second weeding is not necessary because of crop coverage and limited weed growth. Normally two hand weeding are required, but it may restrict to one hand weeding under I/C. in sorghum + red gram or sorghum + cowpea, just one weeding is sufficient to get high yield as in weed- free check.
The critical period of weed free condition may be extended a little longer in I/C than in sole cropping. this is because the critical growth stages of the component crops very temporally in I/C. for example, critical weed free period has to be extended to first 7 weeks in sorghum + red gram I/C while sole sorghum crop requires only requires only 2- 4 weeks weed free period.
Chemical weed control is difficult in intercropping system because the herbicide may be selective to one crop but non- selective to another. Atrazine control weeds in sole sorghum, but it is not suitable for sorghum + red gram intercropping system, as it is toxic to red gram. Herbicides suitable for intercropping systems as-
* Maize + green gram & Maize + cowpea. Butachlor (pre- emergence) (Machete)
* Sorghum + pulse – fluchloriam (PPI) (Basalin) –or Alacholor (pre- emergence) (loss)
* Sorghum + red gram – prometryne (pre- emergence)
* Sugarcane + groundnut – nitro fen (pre-emergence) (to KE -25).
7. Pest and Disease in Intercropping System: Pest and diseases are believed to be less in intercropping system due to crop diversity than sole crops. Some plant combination may enhance soil fungicide and antibiotics through indirect effects on soil organic matter content. The spread of the diseases is altered by the presence of different crops. Little leaf of Brinjal is less when Brinjal is sheltered by maize or sorghum, as the insect- carrying virus first attacks maize or sorghum; virus infestation is less on Brinjal. Non – host plant in mixtures may emit chemicals or odor that affects the pests, thereby protecting host plants.
The concept of crop diversification for the management of nematode population has been applied mainly in the form of decoy and trap crops.
Decoy crops are non-host crops, which are planted to make nematode waste their infection potential. This is affected by activating larva of nematode in the absence of hosts by the decoy crops.
Crop Nematode Decoy crops
Brinjal Meloidogyne incognita Sesamum orientale
Tomato Meloidogyne pratylenchus alleni Caster g.nut
Soybeanpratylenchus sp. Crotalarias spectabills
Trab crops are host crops sown to attract nematode but destined but destined to be harvest or destroyed before the nematode manage to hatch. This is advocated for cryst nematode. The technique involves sowing in pineapple plantations; tomatoes are planted and ploughed in to reduce root knot nematodes. There is also evidence that, some plants adversely affect nematode population through toxic action. Marigold reduces the population of pratylenchus species worms..