I. Nutrient Deficiencies
A. Crops and Soils
Yields of rice and wheat are still constrained by N deficiency on many farms. However, it seems clear from numerous research experiments that N is probably not the major constraint to increasing productivity in the rice-wheat system. Although components of the program address N supply, much of our effort is directed towards other nutrients, especially phosphorus and micronutrients. Deficiencies of micronutrients are clearly increasing in Bangladesh and Nepal, are less recognized, and are not well corrected. The goals of the program in Bangladesh and Nepal are to characterize macro- and micro-nutrient nutrient status of soils in the rice-wheat regions and to develop a range of options to overcome any deficiencies. Limited work is also being carried out in India. Strategies that are being investigated to cope with inadequate nutrient supply include:
Activities in this program component are:
1. Soil Fertility Surveys
Soil fertility surveys are being carried out in the Chuadanga and Dinajpur districts of Bangladesh and the Rupandehi district of Nepal in order to identify soil nutrient constraints to crop production. These districts are national rice-wheat program sites. All sampling sites were geo-referenced for later use with GIS. A total of 125 farmer fields have been sampled in Bangladesh of which 104 have been analyzed; these analyses complement data bases being generated by the Soil Resource Development Institute (SRDI). Samples collected on a 1 km grid in Nepal await analysis.
Soils from the Dinajpur district are generally acid, while those from Chuadanga are generally between pH 7 and 8. Low soil organic matter and organic nitrogen contents are ubiquitous; generally less than 1 and 0.1%, respectively, which is typical of soils in the rice-wheat system, where destruction of aggregates by puddling promotes mineralization of soil organic matter. At Chuadanga, mean levels of P and S are close to the critical level for each nutrient, indicating that responses to these nutrients can be expected at many sites. Levels of available B were below the critical value at all of the sites sampled, suggesting that B deficiency is widespread and that that B additions should be routinely recommended. Of the metal micronutrients, Zn is sometimes below the critical level but Cu and Mn were above critical levels. Soil fertility status is generally poorer in the sandy, acidic soils of Dinajpur.
Summary of Fertility Status of Soils (0-20 cm) in Chuadanga and Dinajpur Districts
n = 77
n = 27
|Total N (%)||0.08||0.04 - 0.13||0.08||0.04 - 0.17||0.12|
|Total OC (%)||0.8||0.3 - 1.3||0.85||0.4 - 1.6||--|
|P (mg/kg)||9.71||1.7 - 33.2||2.42||0.8 - 5.9||10.07|
|K (mg/kg)||1073||39 - 191||592||38 - 84||47|
|S (mg/kg)||8.94||5.0 - 15.7||--||--||10.0|
|Zn (mg/kg)||1.35||trace - 4.4||0.392||0.18 - 1.6||0.68|
|B (mg/kg)||0.0216||0.012- 0.028||0.0446||0.015- 0.106||0.20|
Distribution of Selected Soils Properties (0-20 cm) in Chuadanga Thana
2. Soil Test Based Fertilizer Recommendations
Soil testing programs are not widely available in S. Asia and fertilizer recommendations are generalized based on the results of field experiments in different soils/regions. Experiments to evaluate the benefit of using soil test based recommendations were begun on 4 farms in the Chuadanga district of Bangladesh. Treatments are local farmer practice (T1), BARC standard NPKS recommendation (T2), soil test based recommendation for NPKS plus Zn and B (T3), and soil test based recommendation for NPKS without micronutrients (T4):
Soil Properties of Farms
|Olsen P meq/100gg||
|Avail Zn mg/kg|
Results for 1998-99 wheat crop are shown in the figure. In all cases, soil test based recommendations (T3) gave the highest yields, increasing yields over farmer practice by an average of 18%, (range 13-22%). The BARC standard recommendation (T2) and the soil test recommendation without micronutrients (T4) also increased yields over farmer practice by an average of 7 and 9 %, respectively. Much of the change with these treatments may have been brought about by sulfur, which was included in all treatments except farmer practice. Boron and/or zinc additions significantly increased yields over standard NPKS recommendations. Overall, the benefits of soil test based recommendations were modest, suggesting that nutrient supply was not a major constraint at the yield levels obtained. However, nutrient supply could become more important if other constraints were overcome.
3. On-Farm Evaluation of K and Zn Deficiencies in the Nepal Terai
Analysis of nutrient budgets in experiments with the rice-wheat rotation show large deficits with respect to K and deficiencies are beginning to appear in the Terai of Nepal and in parts of Bangladesh. However, response to K fertilizer is not widely observed in the IGP because most soils contain K-rich minerals.
(i) Rupandehi District
Unreplicated demonstration/diagnosis plots with four treatments were established on 15 farms in Rupandehi district, Nepal; the treatments are control, K, K+Zn, and Zn. The plots were established beginning with wheat in November, 1998. Data is not yet available.
Fertilizer trials were carried out on 4 farms, 2 each in the districts of Rampur Tokani and Parsa, beginning with the 1998-99 wheat season. Treatments included a typical farmer fertilizer rate (T1) and recommended rates of N and P with and without K (T2 and T3). Data from one farm is not yet available. The yield of wheat was increased by 0.8-1.0 t/ha (50%) on 2 of 3 farms but not at all on a third farm when recommended rates on N and P were used. Potassium increased the yield further on all farms by 0.3 to 0.5 t/ha (average of 0.37 t/ha) or from 11-29% (average of 17%). The data indicate that farmers should include K in their fertilizer practice and should use recommended rates of N and P.
A second set of trials evaluated the effect of Zn additions on crop yield. These gave a mean increase of 1.4 t/ha (45%) when zinc was applied to soil, either as zinc sulfate or the commercial product Zinoplex. Sprays (2x) of either material were less effective, indicating that additional applications were needed.
|Zn Treatment||Mean Grain Yield (t/ha)|
|Zn sulfate (20 kg/ha to soil)|
|Zinoplex (15 kg/ha to soil)|
|Zn sulfate spray (2x)|
|Zinoplex spray (2x)|
4. Breeding for Improved Varieties of Rice and Wheat
Plant breeding programs in S. Asia usually make selections under optimal soil fertility conditions, which does not enable identification of lines with the best capacity to extract nutrients from soil nutrient pools. If nutrient efficiency traits are not incorporated into new cultivars, yields may be unnecessarily reduced when crops are grown under conditions of sub-optimal nutrient supply, which are widespread in the region. Unfortunately, plants do not always exhibit visible deficiency symptoms so the existence of a nutrient deficiency may be unrecognized; an example is the response of BR-32 rice to foliar application of micronutrients (see section on seed enrichment with micronutrients).
Plant breeding programs are underway in Bangladesh to identify:
(i) Shorter Season, Drought Tolerant Varieties of Rice for Bangladesh
Shorter season rice varieties would better fit the rice-wheat system and these need to be better adapted to environmental constraints, including low soil nutrient levels. For Aus (spring) season rice, drought tolerance is also desired. The program focus is initially on Aus rice because yields are low, often around 1t/ha and several BRRI lines have failed completely at the Chuadanga site indicating the need for breeding in that environment. Further, plant establishment is more difficult as much of the Aus rice is direct seeded.
In 1998, 56 advanced breeding lines planted by direct seeding were evaluated at Chuadanga for drought tolerance. Twelve lines that showed drought tolerance, resistance to lodging and similar or shorter growth duration than locally used varieties were selected for further testing in the field and greenhouse. The latter will focus on rooting characteristics.
(ii) Phosphorus Efficient Wheat Genotypes
In the rice-wheat system, additions of phosphorus fertilizer are usually needed to correct P deficiency with wheat but not rice because P availability generally increases under flooded conditions. This new breeding strategy is expected to lead to reduced needs for inputs of P fertilizer, which is an expensive import for Bangladesh and is not always available or affordable to farmers.
The breeding program comprises the following sequential components:
- Genotype screening nursery at 0 and 80 kg P2O5/ha
- Preliminary yield trials
- Farmer field trials
- evaluation of best selections on farm as last step prior to release
1997-98 Genotype Screening Nursery at Joydebpur
Yields for Selected Wheat Lines from Screening Nursery at Joydepur and Nashipur
P 0 1
|BAW 898||2.43||4.50||BAW 898||0.95||1.29|
1 best 5 lines without P addition and standard varieties
Screening nurseries contained 52 lines and were established on P deficient soils at two locations, Joydepur and Nashipur. P treatments were 0 and 80 kg P2O5/ha. Several lines that appear to be more P efficient and/or responsive to P addition than the widely used variety Kanchan. Performance of lines was often not consistent across the two sites. One line (genotype 08; Attila) yielded about 1 ton/ha higher than Kanchan without P addition at both sites, but was not the most responsive to P addition. Late planting (Dec. 15 at Joydepur and Dec. 24 at Nashipur) reduced yield potentials. Lines identified on the figure were used in subsequent yield trials.
Preliminary Yield Trials 1998-99 with Lines Selected from 1997-98 Screening Nursery
As with the screening nursery varietal performance was not entirely consistent across sites. For example, the performance of the line Angra was much better than that of line NL560 at Dinajpur but the reverse was observed at Joydebpur. Similarly, the relative performance of BAW923, BAW935 and BAW 943 at both the 0 and 80 kg P2O5/ha levels were different at Jamalpur and Rajshahi.
The standard variety Kanchan performed as well as or better than the newly released variety Sourav (formerly BAW 897) at all sites except Jamalpur. The line Mayoor outperformed Kanchan at Joydepur and is being considered for release. At Jamalpur, the lines BAW 923 and Sourav yielded about 4.5 t/ha with 0 P input compared to 3.8 t/ha for Kanchan and BAW923 gave the highest yield at 80 kg P2O5/ha.
Response patterns to P inputs were more variable at Jamalpur and Rajshahi than at Dinajpur and Joydebpur, possibly reflecting variability in soil P supplying capacity within these sites. The results indicate that careful attention needs to be paid to site selection and management over time as the program progresses. Interactions between P and Zn also need to be considered as high P levels can induce Zn deficiency and many soils in Bangladesh are naturally low in this nutrient.
5. Boron and Crop Sterility
Head sterility, caused by a failure to properly fertilize florets, may affect up to 10% of the area cultivated to wheat in Nepal and Bangladesh. Sterility is erratic and often affects a complete wheat crop on a farm, thereby imposing a severe burden on farm families. The underlying cause of sterility is thought to be B deficiency, however other phloem immobile nutrients could also be involved. Sterility is also often associated with conditions that reduce transpiration (waterlogged soils; cloudy days; high humidity) at the time of pollen tube development and certain modern varieties appear to be genetically susceptible. Probably, there is also an interaction between plant nutrient status, which is related to soil fertility, and environmental conditions.
(i) Experiments at Sipaghat, Nepal - a B Deficient Site:
In the 1996-97 wheat season, substantial sterility was observed in a demonstration of varieties at Sipaghat village, Kabhre district, in the mid-hills region of Nepal. An experiment to evaluate the effect of various micronutrient treatments on sterility and yield was carried out at this location in 1997-98 and again in 1998-99. Two varieties were used, a "susceptible" variety (BL 1135) and a "resistant" variety (RR 21; a widely used variety that is related to Sonalika).
The results of the experiment showed that B deficiency was the sole cause of sterility at this location. Application of B to soil (2 kg B/ha) or by foliar application (0.5 kg B/ha) corrected sterility. In 1997-98, liming (2 t/ha) increased the extent of sterility in BL1135 from 56 to 93% (yield decrease from 1.2 to 0.4 t/ha). Sterility was again overcome by foliar application of B to plants growing in limed soil (yield increase from 0.4 to 2.8 t/ha). No impact of liming was observed in 1998-99.
(ii) Effect of Shading on Sterility
A shading experiment to simulate fog was carried out at Joydepur, Bangladesh, in 1997-98. The variety was Kanchan, the major variety grown in Bangladesh. Shading was for 10 day intervals at a light reduction of 80%, comparable to light levels measured under foggy conditions known to induce or exacerbate sterility. The experiment was repeated in 1998-99 with and without soil and foliar B treatments in order to determine whether increased B supply counteracted the shading effect.
In the both years, maximum sterility was caused by shading between 55-65 days after seeding followed by shading between 45-55 days after seeding. Addition of B did not counteract the shading effect. Possibly shading was too intense to demonstrate a hypothesized B x shading interaction. The result suggests that intense fog at the critical stage in plant development will always induce sterility.
(iii) Survey of Sterility on Farms in NW Bangladesh
In a survey of 25 farmer fields in known problem areas in NW Bangladesh (Dinajpur, Thakurgaon, Panchagar, Rangpur, Kurigram, and Lalmonirhat districts) between March 30-April 5, 1998, sterility in the variety Kanchan was found to vary between 27.5 and 99.5 %. A sterility value of 25% is considered normal for Kanchan, i.e. not all florets have grain. Where possible, soil samples were taken from fields with high sterility and adjacent or nearby fields that had low sterility. Available soil B (hot water extractable B) was not correlated with sterility.
Eighty eight lines were screened for sterility with and without B fertilization on a BARI farm in Rangpur district in 1998-99, however no sterility was observed.
(iv) Screening Wheat Germplasm for Resistance to Sterility
Germplasm screening trials with "pipeline" and released varieties are being carried out at 3 locations in Nepal (Sipaghat and Lumle, in the mid-hills and Bhairahawa in the Terai) with the goal of assessing the contribution of B supply, germplasm, and environment to sterility.
Sterility was not found at Bhairahawa and data from Lumle are not yet available. At Sipaghat, 13 out of 30 lines had unacceptable levels of sterility without B application. Only one of these, Achyut, was a released variety. Sterility was uniformly low with B application of 2 kg/ha to soil.
B. Grain Legumes:
Observations of research experiments and farms, shifts in where legumes can be grown with reasonable success, decreasing grain productivity over time, and soil analyses all suggest that B deficiency also causes sterility in grain legumes in both Bangladesh and Nepal. Other micronutrient deficiencies, especially Zn and Mo and possibly Cu and Mn, are also likely. Experiments carried out by ICRISAT at Rampur, in the inner Terai (Chitwan district) of Nepal showed increased yields of lentil and chickpea with B fertilization. We consider it very important to determine the role that micronutrient deficiencies play in low yields and unreliable grain production as these factors are the major reasons why farmers do not grow these high value crops.
(i) Winter Legumes
Winter legume species could occasionally replace wheat in the rice-wheat rotation. An unreplicated trial with 12 winter legume species, including both forage and grain species was carried out in 1998-99 at Sipaghat, Nepal where B deficiency in wheat has been established. Treatments were with and without B applied to soil at 2 kg/ha.
Vegetative growth of most legumes was substantially enhanced with B fertilization. Lupines and clovers did not grow well, possibly because of the acid soil condition (pH 5.2). Boron addition had an impact on sterility, increasing seed yield of all grain legumes except bitter lupine. More detailed analysis of this experiment is underway.
(ii) Mungbean Relay
Mungbean was relayed into the wheat crop in the boron experiment at Sipaghat, Nepal in 1999 to see if there were any effects of the B, micronutrient and lime treatment combinations on mungbean yield. Unfortunately, unknown persons harvested the plots before the experiment was completed. What data could be gleaned from analysis of the plants suggested that B application increased the number of pods per plant and seeds per pod and decreased the number of unfilled pods per plant. No pods were left on plants in the soil B treatment so we can deduce that this was the most successful treatment. If we see mungbean grown at the village next year we will take credit for successful transfer of technology!!
Pod numbers, seeds per pod and seed size have been declining in soybean seed replication blocks at the Khumaltar site in Nepal. Farmers also report declining yields from soybeans that are planted on bunds of rice paddies and are consequently losing a product with high nutritional value. An experiment to determine if deficiencies of B and/or other micronutrients is the causing these problems is currently underway with several soybean varieties (both vegetable and grain varieties) at the Khumaltar farm.
(iv) Effect of Micronutrients on Yields of Chickpea in Bangladesh
A multi-micronutrient experiment with chickpea was carried out in 1998-99 at the BRRI research station at Joydepur and on a farm in the Chuadanga district. Treatments include an unfertilized control and combinations of NPK, B, and a mixture of Zn, Cu, Mn, and Mo.
Boron addition had no significant effects on yield at either site. At Chuadanga, yield was increased slightly by the complete micronutrient treatment suggesting a response to a micronutrient other than B.
6. Micronutrient Enrichment of Wheat and Rice seed
Stands of wheat outside of the high producing areas, such as the Indian Punjab, are often poor despite seeding rates that are very high. In heavy textured soils, poor seedbed preparation and poor seed-soil contact is a major problem and this has led to no-tillage planting methods that are more successful. Seedbed preparation on lighter textured soils is generally not difficult, which suggests that there are also problems with seed quality that lead to low germination rates and/or seedling survivability. Most farmers produce their own seed, which is generally surface broadcast then worked into the soil by a subsequent tillage or planking operation, which leaves seed at variable depths. Since some seed is planted too deep to germinate, the relative contributions of seed quality and planting technique to poor stand establishment are uncertain. These observations prompted us to combine evaluation of farmer seed performance with testing of the hypothesis that micronutrient enrichment of seeds would lead to greater crop yields because of increased seedling vigor and resistance or tolerance to environmental stresses such as diseases and water deficiency stress. Micronutrient deficiencies (Zn, Mn, Cu etc) are becoming more evident in the region and research on wheat in Australia and Turkey has shown response to micronutrients in the absence of visible crop deficiency symptoms.
Our strategy is to enrich seeds of rice and wheat by foliar application of micronutrients (on research stations) and to evaluate the performance of micronutrient enriched seeds on farms. Ultimately, alternative approaches to increasing the micronutrient content of seeds will be investigated providing positive results are obtained. This research is being carried out in Bangladesh.
A. Experiments with Wheat
Micronutrient enrichment of the variety Kanchan was achieved by foliar sprays of micronutrients applied periodically during crop growth. Treatments varied over years but all included a suite of micronutrients (Zn, Mn, Cu, B, Mo, and Ni) and an untreated control. Other treatments were Zn only and where one element was left out of the complete suite. The variety Kanchan, was grown at the Wheat Research Center at Nashipur, Bangladesh.
Trials were carried out on 15 farmer fields in three thanas in the 1996-97 and 1997-98 seasons and on 9 farmer fields in the 1998-99 season. The farms were mostly different over seasons in order to better establish the frequency of any response. The farmer trials varied in design but the basic objective was to compare yields from seed generated on station, both micronutrient enriched and unenriched, with yields from farmer seed. The experiments consisted of unreplicated plots of six micronutrient treatments in 1996-97; two replicates of two micronutrient treatments in 1997-98 and three replicates of two micronutrient treatments in 1998-99. Seed was planted in rows by hand to avoid problems with seed being sown at different depths. Five farms were selected in each of three thanas in the Dinajpur district. All soils were sandy in texture.
In addition to the field trials, a controlled pot experiment was undertaken to better understand the impacts of micronutrient enrichment on wheat seedling emergence, survival and early growth. Enriched, unenriched and farmer seed from the 97-98 season were planted in soils collected from 3 farms each in Dinajpur Sadar, Kaunia and Kaharol thanas, where responses to micronutrient enriched seed had been observed (see below). Each soil and seed treatment combination was replicated twice. Pots were buried in the ground outside to obtain the field temperature regime.
(i) Enrichment of Wheat Grain by Foliar Application of Micronutrients
1 Data are averages of various treatments with and without added nutrients
Differences all highly significant (p< 0.001)
Substantial increases in seed contents of Zn (2x), Mo (18x) and Ni (27x) and smaller, but significant (p < 0.001), increases in Mn (1.2x) and Cu (1.3x) were achieved in the 1995-96 season. The same patterns were repeated in 1996-97 but micronutrient increases were somewhat less. No yield responses to micronutrient additions were observed during the generation of micronutrient enriched seed and the 1000 grain weight of enriched and unenriched seeds was identical so that suitable unenriched control seeds were generated for use in subsequent studies of the effects of micronutrient enrichment. The micronutrient content of farmer seeds was found to be remarkably similar to our unenriched seed.
Micronutrient Content of Farmer Seed and Station Unenriched Seed
|Farmer seed||---------------------------------------- mg/kg ---------------------------------------|
|Mean ±S.D.||29 ± 5||55 ± 7||4.7 ± 0.6||0.22 ± 0.15||0.16 ± 0.09|
(ii) Impact of Seed Micronutrient Content on Wheat Yields in Farmer Fields
Fourteen farmer sites were harvested in 1996-97 - one was lost to chickens and goats. Using a 15 % increase in yield as the criterion for a yield difference, an increase in production with micronutrient enriched seed compared to farmer seed was observed at six of the fourteen sites. The yield increase at five of these six sites could be attributed to micronutrient enrichment (micronutrient enriched seed gave higher yield than unenriched seed). At one site in Birganj thana, farmer seed was of inferior quality (unenriched seed gave 100% higher yield than farmer seed and equal yield with enriched seed). The mean increase in yield at the five sites where the micronutrient
enriched seed out performed the unenriched seed was 40% or 0.84 t ha-1. In 1997-98, an average yield response to micronutrient enrichment of 0.62 t/ha was obtained on six of fifteen farms. Farmer seed was again of inferior quality at one site, this time in Kaunia thana.
Analysis of yield data from the various micronutrients seed sources used in 1996-97 indicated that the yield response to micronutrient enrichment was caused by Zn at four sites, by Mo at one site, and both Mo and Zn at one site (noted on figure). The data also suggest geographic variability in soil micronutrient deficiency; with Zn deficiency in Kaharol thana, Mo and possibly Zn deficiency in Dinajpur Sadar thana, and no deficiency in Birganj thana. The possible finding of Mo deficiency is interesting in that the high enrichment (23x) of wheat seed achieved by foliar application of Mo does appear to carry over to the following wheat crop; wheat grain grown at Nashipur in 1997 from micronutrient enriched seed generated the previous year contained 1.8x the amount (p <0.001) of Mo in grain grown from unenriched seed. Possibly this elevated seed content of Mo would be sufficient to meet crop needs. Seed soaking with Mo could also be an effective and simple treatment.
(iii) Impact of Seed Micronutrient Content on Emergence and Growth Response in Pot Experiment
Overall, seed enrichment clearly provided an advantage to seedling emergence and plant growth (height) over unenriched (control) and farmer seed. Emergence in Dinajpur Sadar was strongly influenced by seed micronutrient content, whereas in the other two thanas seed micronutrient content and lower quality of farmer seed were both factors. Plant growth did not follow exactly the same pattern as emergence. Some undetermined seed quality factor reduced growth with farmer seed in Kaharol thana, whilst seed enrichment with micronutrients enhanced wheat growth in soils from Dinajpur and Kaunia thanas.
B. Experiments with Rice
(i) Enrichment of Rice Grain by Foliar Application of Micronutrients
|BR-11 Rice 1996||BR-32 Rice 1997|
|----- mg/kg -----|
Foliar applications of micronutrients to rice (BR 11) grown at the Wheat Research Center, Nashipur in the 1996 Aman season increased the seed content of Zn 1.3x, Cu 1.4x, Mo 2.9x and Ni 2.7x and had no effect on Mn content. These small increases were not considered sufficient to warrant evaluation of the seed. In a similar enrichment experiment with two varieties (PR 111 and PR 106) at PAU, India, the contents of Zn, Mn, and Cu were increased 2-3x, 1.5x, and 4-5x, respectively. However, variability in micronutrient content in grain subsamples from the same plot was high, suggesting surface contamination rather than assimilation into grain. Consequently, no trials were carried out with this rice either.
In the 1997 Aman rice season, a second enrichment trial was carried out in Bangladesh because of the possibility that washing of micronutrients from the rice by rainfall reduced micronutrient uptake in 1996. Spray frequency was increased and more attention was paid to weather patterns in an attempt to spray during dry periods. Two varieties (BR 11 and BR 32) were included in this trial and substantial enrichment of Zn, Cu, Mo and Ni was achieved. The three-fold enrichment of Cu was similar to the earlier result at PAU, but is unexpected because plants generally regulate divalent Cu uptake. This result is also in contrast to wheat where enrichment with Cu was slight (1.2x). Either rice has a higher requirement for Cu or possibly Cu in the spray was washed into the floodwater and reduced to the monovalent form, which would be more readily assimilated.
A second, unexpected finding was a 26% yield response to micronutrient sprays with BR 32. No yield response was observed with BR 11, which currently is the standard Aman rice variety. Both Zn (p < 0.05) and possibly Mo (p < 0.1) contributed to the yield response. The yield of BR 32 was 0.44 t /ha lower than that of BR 11 without micronutrient addition but 0.51 t/ha higher with micronutrient addition. The sensitivity of BR 32 to Zn and Mo deficiency has potential implications to the adoption of BR 32 which, as a shorter duration rice (130 days versus 145-150 days for BR 11), was bred specifically for the rice-wheat system; it allows timely planting of wheat to obtain maximum wheat yield. With proper management, use of BR 32 should increase system yield and possibly yields of both rice and wheat.
|Effect of Foliar Application of Micronutrients on Yield of BR 32 and BR 11|
|Complete (Zn, Mn, Cu, B, Mo, Ni)||4.59 a 1|
|Zn only||4.02 b|
|Complete - Mo||4.11 ab|
|Complete - B||4.48 a|
|Variety BR-11 (mean of all treatments)||4.08 b|
1 letters indicate significant difference at p < 0.05
In conjunction with solarization trials, BR-32 was also grown with and without micronutrient sprays on farms in Birganj and Kaharol thanas. Micronutrient sprays at two farms in Kaharol increased yields by 0.7 and 1.4 t/ha (25 and 50%) over the unsprayed controls; whereas in Birganj, micronutrient sprays had no positive effect on yields. This result is consistent with the on-farm trials with enriched wheat seeds, which identified several farms in Kaharol thana as having zinc deficiencies, but found no evidence of micronutrient deficiencies in Birganj thana.
(ii) Impact of Using Micronutrient Enriched Seed on Yields of BR-32 and BR-11 Rice
Micronutrient enriched seed of BR-11 and BR-32 from the 1997 enrichment experiment was used to evaluate the impact of seed micronutrient enrichment on rice productivity at the Wheat Research Center, Nashipur 1998. Enriched seeds were compared with unenriched control seeds. A third treatment tested the effect of additional micronutrient spraying on previously enriched seeds.
Using enriched seed significantly increased the yield of BR-32 by 1.1 t/ha, an increase of 37%. Extra spraying with micronutrients had no benefit, thereby demonstrating that the seed enrichment was sufficient to overcome soil micronutrient deficiencies. The practical implications of this result in terms of organized seed enrichment efforts are still to be determined. Yields from BR-11 were roughly a third of those obtained with BR-32 because of selective attack on this variety by gall midge. No micronutrient treatment effects were observed with BR-11.
7. Integrated Nutrient Management and Integrated Nutrient/ Pest Management
Integrated use of organic and inorganic fertilizer nutrient sources is an ideal that many researchers espouse but which few farmers achieve. The knowledge base for integrated nutrient management is general rather than specific and there is only limited information available on nutrient budgets with different cropping patterns and practices in rice-wheat systems. Return of organic materials to soils is low in many parts of the region because of alternative uses; crop residues are used for animal feed and animal manures are used for fuel. The nutrient contents of manures and composts that are returned to crops are likely to be highly variable and farmers have no way to assess their nutrient content or value. In addition, green manuring is not widely practiced, indicating that returns do not justify the effort for most farmers.
Activities in this area are designed to address knowledge gaps and to use a variety of systems approaches to integrated nutrient management. These include use of legume green manures (LGMs), management of crop residues, and alternative cropping systems and practices. Because adoption of integrated nutrient management practices will probably only occur when multiple benefits are achieved, the research addresses a range of nutrient benefits, direct and indirect, and interactions with pests.
(i) Use of Legume Green Manures
Previous research in the region has evaluated LGMs only in terms of N and with a few legume species, especially sesbania. Since nitrogen fertilizer is subsidized in most of the countries, there is little incentive for using LGMs as a fertilizer substitute. Little systematic work has been undertaken to determine the non-nitrogen benefits from a variety of LGMs or to seek species/practices that target benefits towards specific problems in a particular cropping system. The concept of this knowledge intensive approach is to provide effective options to farmers for fitting LGMs into different agroecological niches, thereby encouraging adoption. Programs were initiated in Nepal and India. They involve initial screening with candidate LGM species and subsequent evaluation of these in the rice-wheat cropping system.
Trials in the mid-hills region with winter legumes were begun in the 1997-98 season and with summer legumes in 1999. The winter season trials were at the research station at Khumaltar in both years and a second trial was carried out at the B deficient Sipaghat site in 1998-99. The summer trials were carried out in farmer fields in the Kathmandu valley (Mahadevstan and Bhakatpur). The focus to date has been on productivity, disease resistance and nutrient uptake by the different species, which include forage and grain legumes and the non-legume mustard. Based on results from the winter and summer trials, a more detailed experiment will be designed to assess system-wide effects of a selected subset of legumes within a rice-wheat rotation.
Data for the summer legume trials is not yet available. Nutrient concentration and total nutrient uptake for winter legume biomass collected at flowering varied considerably by legume species (data on the following page). The concentration of most elements was higher in bitter lupin than the other species (especially for K, S, Zn, Mn [note also sweet lupin] and Mo) but a poor stand restricted total nutrient acquisition. However, this species appears to have the potential to extract large amounts of a range of nutrients if agronomic problems to its production can be overcome. With high biomass production, clover species, especially persian clover, had higher total nutrient uptake (kg/ha) for most nutrients than did other species in the trial.
An experiment with summer legumes was initiated in May 1996 at Ludhiana (PAU) in India. Five legume species (cowpea, mungbean, crotalaria [sunnhemp], clusterbean [guar] and sesbania) and one non-legume (pearl millet [bajra]) were grown during the 60 day period between wheat and rice crops. Soybean and lablab were added in 1997 and 1998. Aboveground biomass was incorporated into soil prior to transplanting rice.
Nitrogen accumulation in above ground biomass was highest with crotalaria and sesbania, then cowpea, mungbean and cluster bean. Considerable N fixation took place if it is assumed that the 20-40 kg N/ha taken up by millet represents available soil N.
Acquisition of other macronutrients and of the micronutrients varied amongst the green manures. Phosphorus concentration ranged between 0.31-0.35% for all species except for crotalaria, which was around 0.21%. At 2.9%, potassium concentration was highest in millet and ranged from 1.0-1.7% in the legume species. Noteworthy amongst the micronutrients was high levels of Mn in cowpea and higher levels of Zn, Cu and Cd in crotalaria relative to the other species. Total nutrient uptake also varied amongst species, with crotalaria, cowpea, and sesbania consistently returning the highest levels of both macro- and micro-nutrients. Manganese uptake (not shown) was highest in crotalaria and cowpea. These differences indicate that much potential exists for tailoring nutrient supply to crops through selection of green manure species.
* letters indicate significant difference at p < 0.05
1 No fertilizer N added to legume treatments; 60 kg N/ha to fallow & pearl millet treatments
2 60 kg N/ha fertilizer added to legume treatments; 120 kg N/ha to fallow & pearl millet treatments
At low N input (A series), rice yields were consistently higher with crotalaria and sesbania green manures. Significant yield increases were also found with all other species in the second year. Green manures had no effect on rice yield at the recommended N rate (B series) in 1996, however, sesbania, crotalaria, cowpea and mungbean green manures significantly increased yields in 1997. Possibly the green manure effect will increase further with time. Wheat yields were not statistically different between treatments; they averaged 4.6 ± 0.1 t/ha in 1996-97 when a single rate of N was added. In 1997-98 only 20kg N/ha was added to A series plots in order to better evaluate if there were residual effects of green manure additions. However, no such effects were seen and yields in the A series averaged 2.5± 0.1 t/ha while those in the B series, which received a full N dose averaged 5.3± 0.1 t/ha.
Root length/densities of the legume species were quite variable. Crotalaria, mungbean and cowpea had relatively deeper rooting compared to sesbania and cluster bean and therefore these species would be potentially more drought resistant. Water availability is a critical factor in the region at this time in the cropping cycle. Pearl millet also showed deep rooting which is consistent with its known drought resistance capabilities. The deeper rooting species might also prove useful as "biological plows" in disrupting compacted soil layers.
(population/250 mL soil)
(population/5 g rice roots)
Previous research indicates that green manures play a significant role in suppressing nematodes and some root diseases. Crop root health measurements during the 1996-97 cropping cycle indicated that the nematode species Tylenchorynchos and Hirschmaniella, were suppressed by several of the green manure species. Sesbania and cowpea suppressed both nematode species, while crotalaria and mungbean suppressedTylenchorynchos and pearl millet suppressed Hirschmaniella in rice.