Thursday, 13 February 2014

Miscalculation mayhem: A note on math and farming

Transplanting day
With members coming from different fields of expertise, we call our team Palay All Stars. Sounds like a powerhouse, eh? However, we had an early tumble at the first hurdle in rice planting: calculating the right amount of seed!

As new rice farmers, it is not in our tacit knowledge to easily give an estimate of how many kilos of seeds we need to sow, what sowing density to follow, and (blame the US and SI metric systems) how big our field is when converted from square meters to hectares (plus decimals and what other fraction—totally, not my language).


It is not of pure genius why our rice field was planted on 30 x 30 cm spacing, with one - three plants per hill.

Sure, wider spacing is good for plant nutrition by reducing overcrowding and competition; it also meant we sowed fewer seeds which lessened our costs. But there’s a backstory to that—

We first realized that something was wrong on transplanting day, when we were basically told by the ES team that we did not have enough seedling trays to plant our field with the mechanical transplanter! According to ES, for the size of survivor fields, they usually prepare 25 trays for sowing. We only had 20—ten each for SL8 and 238.

Wider plant spacing
Needless to say, we were stressed after our first 15 min in the field. How are we going to get five more miracle trays? Do we actually need them? Team RICEsilient who planted on the same day were also short of trays, but they had more than 20 already.

For a good 30 min, we were discussing and trying to re-compute. (This extended to email exchanges until our realization a couple or more of weeks afterwards.)

We concluded, “We should be fine”.

After some helpful advice from the ES team, we decided to plant with wider spacing and lesser plants per hill.

We remained curious though. Our former selves believed our computation for seeding rate and sowing density was smooth. However, we made our calculations just before the Christmas break when we were preoccupied with travel plans and trying to get other work finished before the long break.

We were pretty sure we only need 2 kg of seeds for the whole field. To have some extra, we prepared 4 kg (luckily, this was our saving grace!).  We are still not exactly sure of what went wrong with our calculations, but here is one possible scenario: 
  • Our field’s size is 1500 sq m
  • That means it’s 0.15 ha
  • That’s about 1/15 of a hectare
  • For easier computation, let’s use 1/15
  • That’s 0.07 ha
  • Forget about the previous conversions to not confuse
  • 4 kg for 0.07 ha should be more than enough
If you spotted the error, good! We’re on the same boat (now). Otherwise, think again.
Let’s go back to bullet #2, that’s the conversion we want, which equals 1/7th ha.

Despite the miscalculations— our precautionary act has become beneficial in terms of crop management. The space allowed us to create canals to allow quick drainage for snail control, weed the field using push weeders quite easily; and in the days to come, this should allow our plants to grow bigger and with more tillers.


Mechanical transplanting
“A man must be big enough to admit his mistakes, smart enough to profit from them, and strong enough to correct them”, says the John Maxwell.

Because of some re-computation for fertilizer application, we figured what was wrong. Of course we still want to make profit (higher rice yield) despite the simple math confusion ;)

With relief, the now wiser Palay All Stars, outlines some points to remember for future Rice Survivors:
  • Make sure you get all the data for computation correctly.
  • Do not rush through calculations related to field inputs
  • Check, and double check.
  • Then double check computations with ES.
  • One hectare requires 18-25 kg of seeds if mechanically transplanting,  to transplant a Survivor field, you need about 4 kg (not 2 kg). Sow a few more kilos in case you need to replant; safe number would be 6 kg.
  • If still confused, ask.
However, you may have noticed that there is still one more mathematical issue that needs resolving: The recommended seed rate for mechanical transplanting as mentioned above is 18-25 kg. We sowed 4 kg of seed for 0.15 ha which multiplied by 7 actually equals 28 kg seed per ha, which is more than the recommended rate. But, we still did not have enough trays for one field, let alone enough for spare!

This may be because the recommended rates for mechanical transplanting are incorrect or the seed tray sowing densities were too high, resulting in not enough trays for one field? We are still not clear on this, but it seems that high seed sowing densities are required for mechanical transplanting to allow the machine to pick up enough seedlings on each round. Thus, requiring more seed!

All in all, what we have learnt is that computations are essential in rice production. It will determine how much you’ll spend and invest for your field—consequently; proper allocation of resources (not too much, not too little) can make farming more profitable.

Hopefully, this lucky mistake will turn out well for our rice plants :)

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