Improvement of planosol solum. Part 10: Mixing of wheat straw and corn stalk into subsoil

Based on field cultivation tests by Zhao and soil investigations by Araya, a one-to-one mixing of the second (Aw) and third (B) horizons was conducted to improve the planosol solum in China, leaving the first (Ap) horizon undisturbed by a three-stage subsoil mixing plough. This paper deals with the collection of wheat straws and corn stalks which are left on fields after harvesting by combines, how to mix them into the subsoil and the determination of the limiting length of wheat straw and corn stalk to mix into the subsoil. It was postulated that, if organic matter such as the wheat straw or corn stalk is mixed into the subsoil, where the Aw and B horizons are mixed, low soil hardness may be sustainable because of increased pores within the aggregated formation. The results showed that when a curved plate and a finger-wheel rake were combined, the required straw and stalk collection was obtained. The wheat straws or corn stalks on the soil surface were first collected by the finger-wheel rake and then, dropped by the curved plate, into the furrow at the rear of the third plough body. The collection rates of wheat straws and corn stalks decreased when their lengths were less than 200 and 300mm, respectively. For good mixing with the subsoil, the lengths of both wheat straws and corn stalks should be less than 300 mm. Cutting of the straws and stalks may be necessary to achieve this. (C) 1998 Silsoe Research Institute.