Land growing continuous grain corn as a cash crop loses soil at a rate of

14.0 metric tonnes ha-1 yr-1. This is a fertile soil, which has an organic matter content of 3.8% and nitrogen content of 0.35% (both by mass).

a)
we did this question before,
lost soil=soil mass
14000kg/10000m^2 yr * time=7in*1m/39.37in*1.25E3kg/m^3

time=7/39.37 * 1.25E3 /(1.4) years
and the answer was: 158.7 years..

I don't understand part b!

b) If the entire Ah horizon is lost, calculate how many kg of manure you would need to add per hectare in order to replace the lost organic matter if manure is assumed to be 100% organic matter .

Im not sure but since 14000 kg/ is the soil that is lost per 10000m^2. Do i multipy this by 3.8% to get how much organic material was there?
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Answer this Question

yes, that is the way to find the wt of organic material.

are you sure part a) is correct?

To answer part b of the question, you need to calculate how much organic matter you would need to add per hectare in order to replace the lost organic matter.

First, you correctly calculated that 14,000 kg is the amount of soil lost per 10,000 square meters. To determine how much organic material was lost, you multiply this value by the organic matter content of the soil, which is 3.8%.

So, the amount of organic matter lost per 10,000 square meters is:
14,000 kg * 0.038 = 532 kg

Next, you need to convert this value to the amount of organic matter lost per hectare. There are 10,000 square meters in a hectare, so you can simply multiply the previous result by 10 to get the amount of organic matter lost per hectare:

532 kg * 10 = 5,320 kg

Therefore, if the entire Ah horizon is lost, you would need to add 5,320 kg of manure per hectare to replace the lost organic matter.