Fertilizer use in drylands
8.1 Introduction
No Agricultural system can persist, if it fails to maintain soil fertility. In
dryland soils or SAT soils Nitrogen is universally deficient, ‘P’ is low, and ‘K’ status is
medium to high. The organic matter content of SAT soils is usually less than one per
cent and hence is of low fertility status.
8.2 Low rates of fertilizer application
Vagaries of rainfall and consequent uncertainty of crop performance make
farmers of dryland agriculture to avoid fertilizer application. However, results of
experiments demonstrated yield advantage due to fertilizer use in dry land crop
production.
If the fertilizers are applied to meet the needs of the dryland crops, there may
be prolonged breaks in the monsoon in kharif or limited available moisture in the
root zone of rabi crops may be exhausted before the plants reach reproductive stage
resulting in poor yields. On the other hand, if fertilizers are applied at rates below the
optimum, the yields will be poor. This has to be avoided by assessing the yield
potential of different regions and regulating the soil fertility levels by adding only
such quantities of fertilizers as required for realizing the potential to the maximum
extent possible. Hence fertilizer usage is more in irrigated agriculture than dryland
agriculture.
8.3 Response to Nitrogen
Fertilizer use and loss will be more sensitive in shallow soils; hence response
to applied fertilizer will be less stable on shallow soils. Response to ‘N’ was low and
influence of rainfall was inconsistent among shallow vertisols and alfisols. With
decreasing rainfall, vertisols produced more response to applied fertilizer.
Results indicated that with 40 kg N/ha many crops responded to ‘N’ in
dryland areas by giving about 20 kg extra grain or yield for every kg of N applied.
However, magnitude of response decreased with higher rates except maize crop.
Results of experiments for five years indicated that response of rabi sorghum to 25
kg N/ha on soils with low moisture storage, where as on soil depth up to 60 cm
sorghum grain yield increased up to 75 kg N/ha.
8.4 Response to Phosphorus
Deficiency of phosphorus is less extensive than that of nitrogen. Though
several crops respond to ‘P’ the response is not conspicuous and universal as that of
‘N’. Dry land vertisols possess high phosphorus fixation capacity, ranging from 300 to
450 mg /kg of soil, hence there will be less amount of ‘P’ in soil solution to be
available for the crop plants. This explains the lack of response to ‘P’ in vertisols since
the amount of the ‘P’ added seldom exceed 25-35 kg P2O5/ha which is inadequate to
meet the ‘P’ fixing capacity of the soil and crop requirement. Response of dryland
crops to ‘P’ will continue to remain small and marginal as long as the poor yields of
crops are not increased through efficient soil and moisture conservation measures
and balanced crop nutrition.
8.5 Response to Potassium
On a large scale, potassium has failed to produce distinct response in dryland
cereals and millets as is common with irrigated crops. Dryland soils particularly, the
sandy loam and red soils which are deficient in ‘K’ may respond to moderate levels of
‘K’ when monsoon is normal. The recommended dose of NPK for different crops of
Andhra Pradesh in furnished in table 8.1
Table 8.1 : Recommended dose of fertilizers for rainfed crops of Andhra
Pradesh
Dose (kg/ha)
Crop
N P2O5 K2O
Groundnut 20 40 40
Sorghum 40-80 40 0
Pearl millet 40-80 40 0
Setaria 40 40 0
Redgram 20 40 0
Greengram 20 40 0
Horsegram 10 30 0
Sunflower 30-40 30-40 0
8.6 Response to secondary and micronutrients
Among secondary nutrients oilseeds and pulses respond to sulphur and
calcium. Response to ‘Ca’ and ‘S’ is of typical of rainfed groundnut. Among the
micronutrients deficiency of ‘Fe’ and response to its application have been observed
in crops like chickpea and groundnut. Zinc is deficient in many areas and many crops
respond to Zinc Eg: groundnut, maize, pearl millet etc.
8.7 Response to NPK (Balanced fertilization)
Balanced fertilizer application increases the efficiency of added fertilizers.
Response to universally deficient ‘N’ could be low if other nutrients are limiting.
More frequently ‘P’ limits the response of ‘N’. If N+P is applied the yield response is
increased.
In dryland areas receiving less than 750 mm annual rainfall where prolonged
dry spells are common during the crop period, economical responses were obtained
with low levels of ‘N’ only.
8.8 Alternate sources of Nitrogen
There are several alternate sources of ‘N’, which include organic manures,
biofertilizers, green manuring, introduction of legumes in cropping system etc.,
8.9 Green manuring
This is considered normally uneconomical in drylands. In Khammam district
of A.P, farmers raise green gram with June-July rains and after picking the pods,
plough back the residue and take the sorghum by September (Maghi sorghum). It can
be practiced in vertisols with dependable rainfall. Horsegram can be raised after
sorghum or sunflower during October / November where there is dependable
rainfall. The leaves of Soobabul, Glyricidia etc, can be used as green leaf manure.
8.10 Introduction of legumes in cropping systems
Legume, being a biological ‘N’ fixing crop, should become a part of the
cropping system. Legumes in a cropping system contribute to the extent of 25 kg
N/ha.
8.11 Organic recycling
Vast potential for organic wastes like stubbles of millets and other crops,
sugarcane trash, weeds and other farm residues exist in many areas, which can put to
agricultural use by composting. Conjunctive use of FYM and these organic wastes
improve the productivity of soils especially sandy loam soils by improving their
moisture retentive capacity.
8.12 Rhizobium culture
Inoculating legumes with Rhizobium could not met with success for increasing
‘N’ fixation under dryland conditions probably due to unfavourable environment,
especially prolonged soil moisture stress periods during crop season, high
temperature stress and deficiency of other nutrients.
8.13 Integrated nutrient management system
It envisages the conjunctive use of organic manures, crop residues,
biofertilizers, legumes in crop rotation, green manuring and need based chemical
fertilizers for sustained crop production.
Mean yield of finger millet over a period of 9 years was similar with
recommended NPK rates or with 50% NPK fertilizers along with FYM 10 t/ha. At
Akola (Maharastra) and Kovilpatti (Tamilnadu) incorporation of organic residues
increased sorghum yield by 120 and 75 kg/ha as against 75 and 38 kg / ha with
fertilizers.
Biofertilizers like Azospirillum commonly found in association with roots of
cereals and grasses. High N fixation capacity, low energy requirement and abundant
establishment in the roots of cereals and tolerance to high temperature (30-40° C)
are responsible for its suitability to dry land conditions. It has been largely tested in
sorghum and bajra and can substitute up to 20 kg N/ha.
VAM: Vesicular Arbuscular Mycorrhizae has found to influence yield of
several crops like bajra, finger millet, sorghum, groundnut, pegionpea, cowpea etc. by
increasing ‘P’ uptake.
Phosphate Solubulising Bacteria (PSB) also recieved considerable
attention. Eg: Bacillus sps.
8.14 Salient findings of fertilizer use research in dry land agriculture
The results of fertilizer use research in dry farming areas indicated that
fertilizer dose should be low. Improved cultivars are responsive than local varieties.
The following are the salient findings of research on fertilizer use under
rainfed conditions:
1. Response of crops to fertilizers varied with available soil moisture. Higher
the rainfall, greater the response in shallow soils.
2. Responses to ‘N’ are universal, responses to ‘P’ are obtained on alfisols, and
responses to ‘K’ are limited.
3. Response of post-rainy season crops i.e. rabi crops to fertilizers will depend
on stored moisture in the profile. Most of the nutrients have to be band
placed in the soil at sowing as basal application.
4. For kharif crops, nitrogen can be applied in splits depending on rainfall.
Second split may be avoided if the soil moisture is not adequate for top
dressing in time.
5. Zinc deficiency is indicated in some areas.
6. Balanced fertilizer use resulted in yield advantage during normal rainfall
years.
7. Legumes are more responsive to ‘P’ fertilization.
8. Foliar application of nutrients was not beneficial at several places.
9. Most economical responses were with low rates of 25-30 kg N/ha.
10. On heavy black soils, crops respond to about 30 kg P2O5/ha.
11. Legumes in cropping system contribute to the extent of about 25 kg N/ha
and
12. Integrated nutrient management system appears to be more remunerative.
8.15 Fertilizer use efficiency (FUE) in dryland agriculture
It refers to kg of produce per kg of plant nutrient fertilizer applied.
8.15.1 Factors affecting fertilizer use efficiency
o Choice of cultivars or varieties or varietal selection
o Timely sowing
o Establishment of adequate crop stand
o Time and method of fertilizer application
o Moisture conservation practices and
o Timely weed management
a. Choice of varieties: Choice of varieties will depend on length of the growing
season. The traditional varieties are of long duration and their productivity is low.
High yielding and short duration varieties give more yields and increase the fertilizer
use efficiency.
b. Timely seeding: Timely sowing of a crop is an important agronomic factor
influencing crop yield and therefore the response to fertilizer application. Early
seeding gives good seedling vigour and longer growing season thereby leading to
efficient use of applied fertilizers resulting in higher yields. Delayed sowings in
drylands drastically reduce the yields due to terminal soil moisture stress both in
rainy season and post rainy season crops. Optimum sowing time for rainy season
crops in South India is from June to mid July and post rainy season crops is early
September. Prasad et al., (1988) reported that there is more than 50% reduction in
wheat yields in all the Agro climatic zones of the country when sowings were delayed
from mid November to first fortnight of January. To make up the yield loss due to
delay in sowing, the usual recommendations are higher rate of fertilizer application
leading to low fertilizer use efficiency.
c. Adequate crop stand :One of the major factors for low yields in most of the crops
is inadequate plant population, which is due to inadequate available soil moisture
and soil crusting. The genetical potential of a cultivar is achieved only when optimum
plant population is provided for efficient use of the applied fertilizer. Plant
population of 67,000 plants/ha (in winter maize) application of 200 kg N /ha gave
the same yield as obtained with only 100 kg N/ha at the population of 83000
plants/ha.
d. Time of fertilizer application: Entire phosphorus and potassium requirements of
both kharif and rabi crops are generally applied as basal dose. Split application of N
has been proved to be effective for kharif on light soils. If rains are not received in
time, fertilizer intended for top dressing can be saved. However for rabi crops grown
on stored soil moisture entire N has to be applied at sowing as the chances of
receiving rains after sowing are limited. Fertilizer rates based on the amount of
stored moisture will be more effective than blanket rates.
e. Method of fertilizer application: Placement of P fertilizer near the plant row
proved to be better than the broadcasting in increasing FUE. It is of greater
importance in crops grown on receding soil moisture during post rainy season. This
placement is normally done by seed cum ferti drills.
f. Moisture conservation: Soil moisture is the most limiting factor in dryland
agriculture. Fertilizer use efficiency and water use efficiency are mutually
complementary. Several moisture conservation methods like setline cultivation,
vertical mulch, BBF, recycling of runoff has been recommended for increasing the
FUE.
g. Timely weed control: Weed control has a major impact on crop yield in dry lands.
Weeds compete with crop plants for moisture and nutrients and reduce the crop
yields by 30 to 60%. Keeping the fields weed free especially at early stage of the crop
growth, has given maximum benefits by way of efficient use of scarce soil moisture
leading to higher fertilizer use efficiency and higher yields.