NK-fertiliser high-pH NH3 EF uses wrong list index (7=MAP instead of 8=NK) (SALCAfield_field.py:829-830)

[mklarmann]

Hi team — small index typo in the mineral-fertiliser NH3 emission factors.

The fertiliser list is documented as 0-indexed (SALCAfield/SALCAfield_field.py:787-799): 0=AS, 1=AN, 2=CAN, 3=AH, 4=UREA, 5=UAN, 6=DAP, 7=MAP, 8=NK, 9=NPK, 10=UAS.

Every ef_* pair (lines 817-832) uses the same index on both the low-pH and high-pH lists — except the NK factor:

829  ef_nk_kgNH3_NpkgN = (interpolation_factor*list_low_pH_kgNH3_NpkgN[8]
830                       + (1-interpolation_factor)*list_high_pH_kgNH3_NpkgN[7])

The low-pH term correctly uses index 8 (NK), but the high-pH term uses index 7 (MAP). This is the only mismatched pair in the block, which strongly suggests a typo of 7 for 8.

Why it's a bug: for NK fertilisers at higher soil pH (fi_pH > 5.5), the high-pH contribution to the NH3 emission factor is taken from MAP instead of NK, producing the wrong EF.

One-line fix:

ef_nk_kgNH3_NpkgN = (interpolation_factor*list_low_pH_kgNH3_NpkgN[8]
                     + (1-interpolation_factor)*list_high_pH_kgNH3_NpkgN[8])

Thanks!