濃厚飼料の増与か肥料の増施か? : 営農経済の観点から,青刈トウモロコシの肥料試験成績の検討

抄録

In general farming in Japan the biggest item among the agricultural production cost is the expense for fertilizers. In the case of dairy farmers it is not the fertilizer cost but the expense for concentrated feedstuffs which, on average, is extraordinarily high and by far surpasses the expenses for fertilizers. Both items should be considered together, because in both cases the farmer spends money to buy nutrients which he utilizes to increase his agricultural production: a) plant nutrients, b) nutrients for the animals (TDN). From the point of view of farm economics the best combination of purchased fertilizers and concentrates is reached when the highest effect is obtained at the lowest possible cost. Under this aspect, a fertilizer experiment on green maize, carried out from 1956 to 1958 by the Iwate Pref. Agr. Ex. Stat., was evaluated with the following results: 1) Application of fertilizers up to rates of 120kg/ha N, 186kg/ha P_2O_5 and 204kg/ha K_2O, in addition to 15 t/ha farm-yard manure (FYM), gave strong yield increases, so that the amount of Total Digestible Nutrients (TDN) in the forage was sufficient to feed 5 dairy cows with 15kg milk production per day over a period of 1 month from the green maize obtained from 1/10 ha. Only some additional soybean cake was necessary to balance the TDN/digestible crude protein ratio (=case A). 2) If the same milk yield from 5 cows during 1 month should have been obtained from the forage produced on the experimental plot "FYM only", it would have been necessary to feed more additional concentrates (=case B). 3) Comparison of expenses for concentrates and fertilizers reveals that in the case of this experiment the application of the above fertilizer quantities would reduce the cost of concentrates from 53% (case B) to 14% (case A) of the gross income from milk whereas the fertilizer cost would be not more than 5% of the gross income from milk in case A. 4) Thus the cost of milk production would be greatly reduced due to high application of fertilizers. In this case the expenses for fertilizers +concentrates would decrease from 53% (in case B) to 19% (in case A) of the gross income from milk. 5) In the example of this experiment, therefore, the highest fertilizer application combined with the smallest amount of concentrated feedstuffs was the most profitable combination. 6) If it is possible to generalize this result, one might say: Fertilizer application to forage crops-in high amounts and well-balanced nutrient ratios according to the needs of the plants-is more profitable than the usual practice (in Japan) of heavy use of concentrates.