The most commonly cultivated leguminous crops are clover, beans, and peas. Clover having been already discussed, we need only say a word or two on the manuring of beans and peas.
Beans.
Beans do best on strong land, and, unlike some of the crops considered, do not require a particularly fine tilth. They are generally grown after cereals, and as a rule are sown in spring. More rarely, however, they are sown in autumn. Spring-sown beans take about seven months to come to maturity. They are much affected, like other crops, but to a greater extent, by the nature of the season—a wet season inducing an undue development of straw.
Manure for Beans.
In common practice the manure used for the bean crop is farmyard manure, applied to the soil in autumn after the harvest of the wheat, barley, or other cereal crop grown. So common is this practice, that the belief commonly exists that farmyard manure is necessary for a successful bean crop. But experiments conducted at the Highland Society's Experiment Station at Pumpherston show that full crops of beans may be grown with the aid of artificial manures on soils which have received no application of farmyard manure for ten years.
Relative Value of Manurial Ingredients.
In the Appendix[246] will be found a table giving the results of manurial experiments with the nitrogenous, phosphatic, and potash manures on beans, carried out by Dr A. P. Aitken at the Highland Society's Experiment Station. From these experiments it will be seen that the application of phosphates and nitrogenous manures, either alone or together, exerted a comparatively small effect in increasing the yield of beans compared with that obtained with potash, either alone or combined with phosphates. As Dr Aitken says, "Without potash in the manure, the other two ingredients are of very little use, unless, indeed, the land be very rich in potash."
Gypsum.
Gypsum has a good effect on the bean crop, both on account of the lime it contains, and of its indirect action in setting free potash.
Superphosphate is a much better manure than insoluble phosphates, and similarly, in the few cases where nitrogenous manures are beneficial, the speediest acting are best. Hence nitrate of soda is to be preferred to other nitrogenous manures. When it is applied, it should be applied in small quantities. A slow-acting nitrogenous manure is positively injurious; so also, according to Dr Aitken, is nitrate of soda, applied as a top-dressing to the crop.