Studies on the Seedbed Making Tillage by Rotary Tiller (VI)

Soil Friability under the Sieve Closure

Abstract

We made a soil friability tester to measure pulverizing performance of tilling tine and harrowing tine, and soil friability at various physical conditions of soil.
1) Soil friability is the ability of soil smashing, and is shown by soil friability index and power index for soil pulverizing.
2) When eight kinds of tilling tine is used on three kinds of soil of same type, of different clay content and of constant water content, the result is following:
(1) Soil friability index becomes highest when L-shaped tines N_8-28 are used, followed by N_45-85 tines. Power index for soil pulverizing was minimum when N_8-28 tines are used. (2) So, the soil friability of the tilling tlnes N_8-28 is greater than that of other tines. (3) The pick tine Hn is inferior to other tines in soil friability, and the difference between them is significant on analysis of variance (4) As clay content of soil becomes higher, soil friability index becomes lower and power index for pulverizing becomes higher, that is, soil friability becomes lower. (5) The faster the cutting speed of tilling tine, the higher the soil friability index. But at the same time, pulverizing horsepower and the power index for soil pulverizing become higher. (6) Power index for soil pulverizing, shown as a function of clay content (C_C) of soil and cutting speed (V_C) of tilling tine, indicates high index in proportion to log C_C and log V_C. (7) soil friability index goes down in linear line as C_C increases, and goes up in exponential function as V_C increases.
3) In case of widly varying water content of three kinds of soil which have different clay content, the results are as follows: (1) As water content increases, soil friability index becomes lower. But it turned ioto a curve around the point of plastic limit (PL) i. e. consistency index (I_C)=1.0, and indicates quadric fall. When handle this as a function of I_C, the relation that the soil friability index becomes higher in proportion to log I_C is found generally. (2) Power index for soil pulverizing decreases gradually with increasing water content. Then, it suddenly turnes into increase at the point of water content of PL:I_C=1.0. The minimum index is around the point of I_C=1.0 of water content. In both case of I_C≥1.0 and I_C≤1.0, the index is a exponential function of I_C. (3) Soil friability index at the point of plastic limit (PL) shows little change by varying clay content, though a little higher in lower content. Similarly, power index for soil pulverizing increases in proportion to C_C, drawing a linear proportion line.
4) To make the seedbed with proper sized clods, using a sieve of a fixed mesh, it will be better to use such tilling tines as L-shaped groups with long horizontal cutting edges. The range of water content suitable for soil pulverizing is around the point of plastic limit i. e. I_C=1.0.