In this article we will discuss about the water management for maize crops.
Maize is an efficient user of water in terms of dry matter production and among cereals it is potentially the highest yielding grain crop. Although, in deep soils, the roots may reach a depth of 2 m, the highly branched system is located in upper 0.8 to 1.0 m and about 80 per cent of the soil water uptake occurs from this depth. In regions receiving rainfall around 600 mm during the crop season, there may not be any necessity for irrigation.
Excess moisture affects germination of maize seed. On well drained lateritic soil, germination of seed in furrows 5 and 25 cm deep, decreased from 84 and 87 per cent, respectively without submergence to 29 and 38 per cent after 5 days submergence germination reduced from 98 to 47 per cent in water saturated soil. Flooding for 6 hrs reduced germination to only 57-65 per cent. Most sensitive period was one to two days after seeding.
1. Critical Stages for Irrigation:
Frequency and depth of irrigation has pronounced effect on grain yield. Maize appears relatively to tolerate water deficits during vegetative phase and ripening periods. Until the plants are 30 to 40 cm high, transpiration is limited and the daily requirement being approximately 3-4 mm a day. Evapotranspiration reaches a peak of 8-12 mm a day during tasseling, earing and pollination.
Most critical stage for irrigation is flowering period (15-20 days) including tasseling, silking and pollination. Greatest decrease in grain yield is caused by water deficits during this stage, mainly due to reduction in grain number per cob. Moisture stress during this period may cause the tassel and upper leaves to dry. The tassel may fail to shed viable pollen and fertilisation will be only partial.
During the five weeks that follow tasseling, water use is about 50 per cent of the seasonal requirement. Water stress during kernel development period may lead to reduced grain yield due to reduction in grain size. Water deficits during ripening period have little effect on grain yield.
Importance of adequate available soil moisture during flowering has been confirmed by several workers. It has been shown that when soil moisture is depleted to wilting point, even for a day or two during tasseling or pollination period, grain yields were reduced by over 20 per cent and if the stress was for six to eight days, yields were reduced by 50 per cent. The time at which moisture stress occurs during the critical stages also affect yield (Table 4.7).
TABLE 4.7: Effects of stress for a week on maize yield.
In an irrigation trial at Bulgaria, maize crop was given four irrigation or had irrigation reduced by decreasing the amount of water supplied at each irrigation by 20, 40 or 60 per cent or by omitting first, second, third or fourth irrigation. Average yields were 4.63 t ha-1 with no irrigation, 14 t ha-1 with full irrigation and were reduced by 4-11 per cent by reducing the number of irrigations and by 4-23 per cent by reducing the amount of irrigation water supplied at each irrigation.
2. Irrigation Scheduling:
For adequate stand establishment, the root zone should be wetted at or soon after seeding. The water depletion levels for irrigation schedules are 40 per cent during establishment, 50-65 per cent during vegetative period, 40 per cent at flowering and 80 per cent during ripening period. In terms of IW/CPE ratio, irrigation can be scheduled at 1.2 during establishment, 0.75 during vegetative phase, 1.2 during flowering and 0.5 during ripening phase.
Under conditions of limited irrigation water, irrigation scheduling should be based on avoiding water deficit during flowering followed by grain development period. If shortage of water is unavoidable, water may be saved by reducing the supply during vegetative stage as well as during grain filling stage.
Sandy soils with low moisture retentivity may require around 8 irrigations during rabi. Keeping the total quantity of water constant, high frequency irrigation with smaller depth (40 mm) at each irrigation minimises deep percolation losses leading to higher water use efficiency.
As indicated earlier, maize crop flourishes well on well drained soils. Waterlogging should be avoided, particularly, during flowering and grain development. Waterlogging at flowering can reduce grain yield by about 50 per cent. For optimum yield, a cultivar of 110-120 days duration requires 500 to 750 mm of water depending on soil and climate.
3. High Yield in Rabi:
Though the crop responds to better management both in kharif and rabi, erratic rainfall restricts timely field operations (field preparation, timely sowing, weed management etc.) in kharif. In the absence of any major environmental impediments in rabi, desired management practices can be carried out in optimum time for the advantage of the crop. In the absence of major insect and pest problem, additional inputs adds to high maize yield.
Major factors among others, favouring rabi maize include the following:
i. Better water management:
In the absence of rainfall vagaries, rabi maize does not suffer waterlogging and pests and diseases infestation. Timely crop management practices are to the advantage of optimum growth and crop development during rabi.
ii. Favourabe temperature:
Maize plants during rabi tends to be more effective in view of lower photorespiration losses because of lower night temperature and larger effective photosynthetic leaf surface. Longer crop duration leads to accumulation of higher dry matter for higher yield.
iii. Better response to nutrients and other inputs:
Favourable growing conditions during rabi improves response of maize to added fertiliser and other inputs. With better response to fertilisers and other inputs, there will be considerable improvement in the profits from rabi maize relative to kharif maize.
iv. Plant protection:
Extent of damage due to pests and diseases is higher in kharif than, in rabi. This is largely due to low humidity in rabi. The losses due to pests and diseases in thus minimised during rabi.
v. Weed Management:
In kharif, weeds pose major threat to maize yield. Continuous rains during peak monsoons, usually, do not permit timely intercultivation, manual weeding or herbicides use. Such problems does encounter during rabi. As such, rabi maze yields will be higher than that during kharif.