Dear Nilay Borah,

could it be that the transplanted seedlings take nutrients from another horizon just below the top horizon while the sown seeds must take it from the smallest top layer that lacks even more nutrients? Was the stubble perhaps better decomposing just below the top horizon, making nutrients better available just below the top layer, compared with the very surface layer, the very top horizon?

Best regards, Kees

Dear Nilay Borah,

could it be that the transplanted seedlings take nutrients from another horizon just below the top horizon while the sown seeds must take it from the smallest top layer that lacks even more nutrients? Was the stubble perhaps better decomposing just below the top horizon, making nutrients better available just below the top layer, compared with the very surface layer, the very top horizon?

Best regards, Kees

Dear Nilay Borah:

I agree with what mentioned CJ Stigter, material thickness, rice stubble must be checked, since in the first instance the seed germinates and develops in a suitable environment humidity, but the next step, the rice seedlings and wheat require a good supply of nitrogen, be it in ammoniacal or nitratros, in addition to bacteria, algae and fungi that can help the seedling development, but these microorganisms are below stubble, by the above, it is relevant check thickness stover and rhizosphere of each of the cultures.

 Dr.Borah, interesting observation.I presume that  the vegetable seedlings were transplanted slightly deeply and rice and wheat seed were sown in surface layer.It means that both the groups are feeding in different zones as pointed out by Dr.Stigter.Dr. Antonio is also right that the N requirement of rice and wheat are more than the vegetable crops.The residual soil nutrients in the lower layer may be meeting the N requirement of vegetable seedling whereas the surface layer may not be supplying sufficient N to cereal seedlings.Also,it appears that the rice stubbles are not incorporated in soil.It means that N immobilization is not conspicuous in lower layer and so vegetable seedling get  soil nutrients.

Excellent observations by our colleagues. I do not think Nilay , despite decomposable cabon , such differential crop response is anyway , attributable to such carbon source , since time lag for such obervation is very short. It is the response of residual nitrogen , concentrated to different soil  layers and crops , vegetables fed little deeper , while  rice/wheat seeds sown on the surface soil layer?

Dear colleagues (C J Stigter, A F Diaz, A S Rao, A K Srivastava),

Thanks for your observations and comments. We agree with your observations regarding nutrient uptake from different soil layers in each case for cereals and vegetables. In this context we would like to seek your comments on following observations.

The yellowing was observed during 3rd to 4th week after sowing of rice and wheat (but not for Vigna radiata L. or vegetables).

The root mass at that stage varied from 0.19 to 0.21 g (rice), 0.18 to 0.23 g (wheat) with nitrogen uptake of 3.6 to 3.9 mg (rice) and 3.9 to 4.3 mg (wheat) per plant compared to root mass of 5.5 to 8.1 g/plant (vegetables), all under unfertilized conditions.

Considering low nutrient turnover in cereals than vegetables (nutrient uptake was not estimated), can we think that the rhizosphere effects of bacteria, fungi, algae had a dominant role. Since seedlings of vegetables are transplanted the roots possess consortia of microorganisms which adapt well in the new environment by the time plants start mining increasing quantities of nutrients. But, as the seeds of cereals germinate under an environment witnessing decomposition of crop residues, the root colonization (hypothetical) by microbes receive hostile reaction from the native organisms.  So, we may endorse what suggested by A F Diaz, the rhizosphere of each crop needs to be studied, especially cereals. Dear colleagues, your valuables comments welcome.

Decomposable rice stubble requires nitrogen to feed microorganisms in the process of decomposition. This Nitrogen is taken from the soil or from a fertilizer source (when available). The young rice and wheat plants needs labile nitrogen to grow, but they are not able to compete with the microorganisms. This causes yellowing in the first stages of the plants due to lack of nitrogen. The plants become normal as they grow and the decomposition of the straw are completed. After this, the rice plants become normal, providing the other nutrients are also available.

The seedlings of brinjal, chilli, tomato, probably are not visually affected, which does not mean that they are completely satisfied with N that they need.

In case of rice and wheat seedlings, the immobilization of nitrogen by decomposing stubbles limited the N nutrition as explained by Dr. Galerani .Under waterlogged conditions of rice the immobilization of N can continue up to at least 4 weeks or continue even up to 20 weeks( with very high C:N ratio materials), in incubation studies.But mineralization can start from around 4 weeks on wards and continue up to around 16 weeks.Initial mineral N in soil and mineralized N from soil organic N also play role in  rice stubble decomposition and mineralization. In case of vegetable seedlings which are transplanted some what deep ,the  initial mineral N in soil and some mineralized N from soil organic N may also be playing role in their N nutrition (before waiting  for the release of mineral N from decomposing rice stubbles).Many times it is recommended to incorporate rice straw or stubbles one month before transplanting rice seedlings.However ,the whole scenario may change if recommended rate of N application through fertilizer is made or green manure is applied.Fertilizer N application  or green manuring not only facilitates early decomposition of stubbles  by lowering C:N ratio but also N release through mineralization. 

I do agree with Dr.Galerani's reasoning. The delays that Dr. Rao mentions are also involved. Much of the nutrient cycling and disease suppression needed by plants occurs immediately adjacent to roots, so in the rhizosphere. Only that knowledge makes the picture complete.

Best regards, Kees

Dear colleagues,

Thanks for interesting and useful discussion. Do we still need to work on response of crop species to these situations? Because, the Vigna radiata L. young plants (sown almost at the same time that of dry direct seeded rice and one month after transplanting of vegetable seedlings) did not show yellowing.

Dr.Borah,please remember that Vigna radiata L. is a legume which can fix atmospheric N2. Of course some residual N is there in soil as nitrate or ammonium form.Estimates of depth-wise distribution of mineral N ,mineralization soil organic N and added straw or stubbles(with or without N supplementation) during crop growth period will enhance our understanding of N supply dynamics to direct sown and transplanted crops.The knowledge generated may help us to fine-tune our N recommendations to crops.

I think that Dr. Rao is right in that we still have to fine tune our N knowledge. Also in sole rice crops there are situations with much too high N given as well nitrogen (and other such as potassium) deficiencies.

Answering questions from our rice farmers on Java and Lombok the day before yesterday, one of the former complained about yellowing leaf tips which much have been due to such a deficiency (potassium here most likely). So fine tuning of nutrients for different crops/varieties and crop densities is still necessary in the very practice of day to day farming.

Best regards, Kees

We also need to see the nutrient release pattern from such un-decomposed material and also the differential nutrient requirement of different crop in terms of length of growing period .

We agree Parameshwar Shirgure sir, and are doing it. Thanks

i want to add something. a) root pattern of theses crop should be checked b) NUE should also be checked to have a more clear idea.

Thank Waqas, it's a good point. We are monitoring just physical (mass, volume0 parameters. May be we should try determining more pertinent (CEC etc) properties.