The balance principle for nitrogen compared to production functions.

Calculations on field experiment data.

Factors determining the optimum rate in the individual case.

Soil nitrogen delivery (soil characteristics, annual situation for mineral N and mineralization.

Crop development (stand, weather, other growth factors, weeds, diseases)

Of these only some soil characteristics are constant, the others vary depending on the annual situation. However, experience over a span of years will give estimates for a ”normal” situation and possible variations.

The situation for a farmer or advisor is that beforehand he knows only soil characteristics, some data about previous situations, for winter crops he can get information of plant densities etc.

Different strategies are possible.:

Use a general recommendation based on experiments in the area. In Sweden yield functions are determined and the recommendation is dependent on price relations. Adjustments for actual soil analyses are made.

Use a yield dependent estimate based on previous yields. A balance principle.

Use a two-step stragegy: apply a low base rate at ”normal time”, apply a complementary dressing later when the stand and crop development is better known. Preferably sensor guidance.

Calculations on data from field experiments.

Data from published experimental reports were used to investigate the consequences of different strategies.

Soil and yield data from 19 locations and 55 experimental years are used for this study. This means that in average about 3 experiments have been located on the same farm and in 8 locations even on the same field but on a new site. This has an importance. We can establish the variation in optima between years for the same farm or even field.

Function: a third degree polynomial was fitted to the average experimental yields on the same site. That means that an advisor had 3 years of concrete background from the actual site, which is a very priviledged situation.

Balance principle: the actual yields from the site were used. 2 % N in grain was assumed and corrections were made for soil mineral N analysis where available.

2-step strategy: 70% of estimated balance dressing was applied as a base. Sensor governed addition, where needed, was applied later.

The following summary table contains data for all sites. The optima are average for all years at respective site. For ”function” and ”balance” the same recommendation is applied every year, for ”precision” there is annual adjustment.

Site	Recomm. ”Balance”	Opt(10) kg N	Opt(5) kg N	Bal-funk(10) SEK/ha*y	Bal-funk(5) SEK/ha*y	Prec-funk(5) SEK/ha*y
Ås	90	98	113	54	77	210
Ösaker	110	126	155	2	-13	361
Jyndevad	130	130	142	0	-117	43
Askov	100	108	156	-9	-191	533
Jokioinen	60	62	92	70	0	533
Peipohja	50	20	84	-22	98	433
Everöd	50	57	92	-65	127	932
Pinan	110	108	128	0	-70	386
Herrestad	130	145	169	144	227	405
Ormastorp	140	123	>200	-8	-398	240
Skrävlinge	140	121	>200	51	-653	27
Uppåkra	150	145	161	12	-140	19
Linelund	100	97	133	169	51	171
Åstorp	170	178	196	5	-233	175
Badene	160	158	185	15	-255	185
Skofteb ML	150	164	>200	-6	-345	0
Skofteby Mj	160	132	141	40	144	684
Hästhalla	170	169	185	-5	-10	212
Brunnby	160	193	253	-223	-620	158
Average	123	123	157	12	-122	300

The Balance Principle has given almost the same result as the function with price relation 10. This is to be expected since that price relation is agronomically fairly sound. With price relation 5 the average ecomic optimum is 157 kg N/ha compared to 123 for price relation 10 and Balance Principle. With these prices there is an average difference of SEK 122 at a disadvantage for the balance principle. But on the other hand: switching from Balance Principle to Function with these prices means an increase in nitrogen use with 34 kg N and an average yield increase of 60 kg grain per hectare. There is a disproportion between input and result which is not acceptable.

If we switch to precision application there is a possible gain of SEK 300 per hectare, extra costs not considered.

We can conclude that a balance principle works also for nitrogen. There might be a small economical loss the relation between product prices and nitrogen is such that the efficiency of nitrogen is very low at the theoretical optimum rate. However, this is not a sustainable situation and should be avoided. Which we do by using the balance principle as a base and adjust according to the situation the actual year.

Give priority to ecology – and economy will follow.

Data from the experiment in the form of yield curves, individual yield data and net economy for the Nordic project and the Swedish field experiments (text only in Swedish so far, but the important information is visual).